tablecmds.c

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/*-------------------------------------------------------------------------
 *
 * tablecmds.c
 *    Commands for creating and altering table structures and settings
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/commands/tablecmds.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/genam.h"
#include "access/heapam.h"
#include "access/heapam_xlog.h"
#include "access/multixact.h"
#include "access/reloptions.h"
#include "access/relscan.h"
#include "access/sysattr.h"
#include "access/xact.h"
#include "catalog/catalog.h"
#include "catalog/dependency.h"
#include "catalog/heap.h"
#include "catalog/index.h"
#include "catalog/indexing.h"
#include "catalog/namespace.h"
#include "catalog/objectaccess.h"
#include "catalog/pg_collation.h"
#include "catalog/pg_constraint.h"
#include "catalog/pg_depend.h"
#include "catalog/pg_foreign_table.h"
#include "catalog/pg_inherits.h"
#include "catalog/pg_inherits_fn.h"
#include "catalog/pg_namespace.h"
#include "catalog/pg_opclass.h"
#include "catalog/pg_tablespace.h"
#include "catalog/pg_trigger.h"
#include "catalog/pg_type.h"
#include "catalog/pg_type_fn.h"
#include "catalog/storage.h"
#include "catalog/toasting.h"
#include "commands/cluster.h"
#include "commands/comment.h"
#include "commands/defrem.h"
#include "commands/sequence.h"
#include "commands/tablecmds.h"
#include "commands/tablespace.h"
#include "commands/trigger.h"
#include "commands/typecmds.h"
#include "common/relpath.h"
#include "executor/executor.h"
#include "foreign/foreign.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "nodes/parsenodes.h"
#include "optimizer/clauses.h"
#include "optimizer/planner.h"
#include "parser/parse_clause.h"
#include "parser/parse_coerce.h"
#include "parser/parse_collate.h"
#include "parser/parse_expr.h"
#include "parser/parse_oper.h"
#include "parser/parse_relation.h"
#include "parser/parse_type.h"
#include "parser/parse_utilcmd.h"
#include "parser/parser.h"
#include "rewrite/rewriteDefine.h"
#include "rewrite/rewriteHandler.h"
#include "rewrite/rewriteManip.h"
#include "storage/bufmgr.h"
#include "storage/lmgr.h"
#include "storage/lock.h"
#include "storage/predicate.h"
#include "storage/smgr.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/fmgroids.h"
#include "utils/inval.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/relcache.h"
#include "utils/snapmgr.h"
#include "utils/syscache.h"
#include "utils/tqual.h"
#include "utils/typcache.h"


/*
 * ON COMMIT action list
 */
typedef struct OnCommitItem
{
    Oid         relid;          /* relid of relation */
    OnCommitAction oncommit;    /* what to do at end of xact */

    /*
     * If this entry was created during the current transaction,
     * creating_subid is the ID of the creating subxact; if created in a prior
     * transaction, creating_subid is zero.  If deleted during the current
     * transaction, deleting_subid is the ID of the deleting subxact; if no
     * deletion request is pending, deleting_subid is zero.
     */
    SubTransactionId creating_subid;
    SubTransactionId deleting_subid;
} OnCommitItem;

static List *on_commits = NIL;


/*
 * State information for ALTER TABLE
 *
 * The pending-work queue for an ALTER TABLE is a List of AlteredTableInfo
 * structs, one for each table modified by the operation (the named table
 * plus any child tables that are affected).  We save lists of subcommands
 * to apply to this table (possibly modified by parse transformation steps);
 * these lists will be executed in Phase 2.  If a Phase 3 step is needed,
 * necessary information is stored in the constraints and newvals lists.
 *
 * Phase 2 is divided into multiple passes; subcommands are executed in
 * a pass determined by subcommand type.
 */

#define AT_PASS_DROP            0       /* DROP (all flavors) */
#define AT_PASS_ALTER_TYPE      1       /* ALTER COLUMN TYPE */
#define AT_PASS_OLD_INDEX       2       /* re-add existing indexes */
#define AT_PASS_OLD_CONSTR      3       /* re-add existing constraints */
#define AT_PASS_COL_ATTRS       4       /* set other column attributes */
/* We could support a RENAME COLUMN pass here, but not currently used */
#define AT_PASS_ADD_COL         5       /* ADD COLUMN */
#define AT_PASS_ADD_INDEX       6       /* ADD indexes */
#define AT_PASS_ADD_CONSTR      7       /* ADD constraints, defaults */
#define AT_PASS_MISC            8       /* other stuff */
#define AT_NUM_PASSES           9

typedef struct AlteredTableInfo
{
    /* Information saved before any work commences: */
    Oid         relid;          /* Relation to work on */
    char        relkind;        /* Its relkind */
    TupleDesc   oldDesc;        /* Pre-modification tuple descriptor */
    /* Information saved by Phase 1 for Phase 2: */
    List       *subcmds[AT_NUM_PASSES]; /* Lists of AlterTableCmd */
    /* Information saved by Phases 1/2 for Phase 3: */
    List       *constraints;    /* List of NewConstraint */
    List       *newvals;        /* List of NewColumnValue */
    bool        new_notnull;    /* T if we added new NOT NULL constraints */
    bool        rewrite;        /* T if a rewrite is forced */
    Oid         newTableSpace;  /* new tablespace; 0 means no change */
    /* Objects to rebuild after completing ALTER TYPE operations */
    List       *changedConstraintOids;  /* OIDs of constraints to rebuild */
    List       *changedConstraintDefs;  /* string definitions of same */
    List       *changedIndexOids;       /* OIDs of indexes to rebuild */
    List       *changedIndexDefs;       /* string definitions of same */
} AlteredTableInfo;

/* Struct describing one new constraint to check in Phase 3 scan */
/* Note: new NOT NULL constraints are handled elsewhere */
typedef struct NewConstraint
{
    char       *name;           /* Constraint name, or NULL if none */
    ConstrType  contype;        /* CHECK or FOREIGN */
    Oid         refrelid;       /* PK rel, if FOREIGN */
    Oid         refindid;       /* OID of PK's index, if FOREIGN */
    Oid         conid;          /* OID of pg_constraint entry, if FOREIGN */
    Node       *qual;           /* Check expr or CONSTR_FOREIGN Constraint */
    List       *qualstate;      /* Execution state for CHECK */
} NewConstraint;

/*
 * Struct describing one new column value that needs to be computed during
 * Phase 3 copy (this could be either a new column with a non-null default, or
 * a column that we're changing the type of).  Columns without such an entry
 * are just copied from the old table during ATRewriteTable.  Note that the
 * expr is an expression over *old* table values.
 */
typedef struct NewColumnValue
{
    AttrNumber  attnum;         /* which column */
    Expr       *expr;           /* expression to compute */
    ExprState  *exprstate;      /* execution state */
} NewColumnValue;

/*
 * Error-reporting support for RemoveRelations
 */
struct dropmsgstrings
{
    char        kind;
    int         nonexistent_code;
    const char *nonexistent_msg;
    const char *skipping_msg;
    const char *nota_msg;
    const char *drophint_msg;
};

static const struct dropmsgstrings dropmsgstringarray[] = {
    {RELKIND_RELATION,
        ERRCODE_UNDEFINED_TABLE,
        gettext_noop("table \"%s\" does not exist"),
        gettext_noop("table \"%s\" does not exist, skipping"),
        gettext_noop("\"%s\" is not a table"),
    gettext_noop("Use DROP TABLE to remove a table.")},
    {RELKIND_SEQUENCE,
        ERRCODE_UNDEFINED_TABLE,
        gettext_noop("sequence \"%s\" does not exist"),
        gettext_noop("sequence \"%s\" does not exist, skipping"),
        gettext_noop("\"%s\" is not a sequence"),
    gettext_noop("Use DROP SEQUENCE to remove a sequence.")},
    {RELKIND_VIEW,
        ERRCODE_UNDEFINED_TABLE,
        gettext_noop("view \"%s\" does not exist"),
        gettext_noop("view \"%s\" does not exist, skipping"),
        gettext_noop("\"%s\" is not a view"),
    gettext_noop("Use DROP VIEW to remove a view.")},
    {RELKIND_MATVIEW,
        ERRCODE_UNDEFINED_TABLE,
        gettext_noop("materialized view \"%s\" does not exist"),
        gettext_noop("materialized view \"%s\" does not exist, skipping"),
        gettext_noop("\"%s\" is not a materialized view"),
    gettext_noop("Use DROP MATERIALIZED VIEW to remove a materialized view.")},
    {RELKIND_INDEX,
        ERRCODE_UNDEFINED_OBJECT,
        gettext_noop("index \"%s\" does not exist"),
        gettext_noop("index \"%s\" does not exist, skipping"),
        gettext_noop("\"%s\" is not an index"),
    gettext_noop("Use DROP INDEX to remove an index.")},
    {RELKIND_COMPOSITE_TYPE,
        ERRCODE_UNDEFINED_OBJECT,
        gettext_noop("type \"%s\" does not exist"),
        gettext_noop("type \"%s\" does not exist, skipping"),
        gettext_noop("\"%s\" is not a type"),
    gettext_noop("Use DROP TYPE to remove a type.")},
    {RELKIND_FOREIGN_TABLE,
        ERRCODE_UNDEFINED_OBJECT,
        gettext_noop("foreign table \"%s\" does not exist"),
        gettext_noop("foreign table \"%s\" does not exist, skipping"),
        gettext_noop("\"%s\" is not a foreign table"),
    gettext_noop("Use DROP FOREIGN TABLE to remove a foreign table.")},
    {'\0', 0, NULL, NULL, NULL, NULL}
};

struct DropRelationCallbackState
{
    char        relkind;
    Oid         heapOid;
    bool        concurrent;
};

/* Alter table target-type flags for ATSimplePermissions */
#define     ATT_TABLE               0x0001
#define     ATT_VIEW                0x0002
#define     ATT_MATVIEW             0x0004
#define     ATT_INDEX               0x0008
#define     ATT_COMPOSITE_TYPE      0x0010
#define     ATT_FOREIGN_TABLE       0x0020

static void truncate_check_rel(Relation rel);
static List *MergeAttributes(List *schema, List *supers, char relpersistence,
                List **supOids, List **supconstr, int *supOidCount);
static bool MergeCheckConstraint(List *constraints, char *name, Node *expr);
static void MergeAttributesIntoExisting(Relation child_rel, Relation parent_rel);
static void MergeConstraintsIntoExisting(Relation child_rel, Relation parent_rel);
static void StoreCatalogInheritance(Oid relationId, List *supers);
static void StoreCatalogInheritance1(Oid relationId, Oid parentOid,
                         int16 seqNumber, Relation inhRelation);
static int  findAttrByName(const char *attributeName, List *schema);
static void AlterIndexNamespaces(Relation classRel, Relation rel,
                     Oid oldNspOid, Oid newNspOid, ObjectAddresses *objsMoved);
static void AlterSeqNamespaces(Relation classRel, Relation rel,
                   Oid oldNspOid, Oid newNspOid, ObjectAddresses *objsMoved,
                   LOCKMODE lockmode);
static void ATExecValidateConstraint(Relation rel, char *constrName,
                         bool recurse, bool recursing, LOCKMODE lockmode);
static int transformColumnNameList(Oid relId, List *colList,
                        int16 *attnums, Oid *atttypids);
static int transformFkeyGetPrimaryKey(Relation pkrel, Oid *indexOid,
                           List **attnamelist,
                           int16 *attnums, Oid *atttypids,
                           Oid *opclasses);
static Oid transformFkeyCheckAttrs(Relation pkrel,
                        int numattrs, int16 *attnums,
                        Oid *opclasses);
static void checkFkeyPermissions(Relation rel, int16 *attnums, int natts);
static CoercionPathType findFkeyCast(Oid targetTypeId, Oid sourceTypeId,
             Oid *funcid);
static void validateCheckConstraint(Relation rel, HeapTuple constrtup);
static void validateForeignKeyConstraint(char *conname,
                             Relation rel, Relation pkrel,
                             Oid pkindOid, Oid constraintOid);
static void createForeignKeyTriggers(Relation rel, Constraint *fkconstraint,
                         Oid constraintOid, Oid indexOid);
static void ATController(Relation rel, List *cmds, bool recurse, LOCKMODE lockmode);
static void ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
          bool recurse, bool recursing, LOCKMODE lockmode);
static void ATRewriteCatalogs(List **wqueue, LOCKMODE lockmode);
static void ATExecCmd(List **wqueue, AlteredTableInfo *tab, Relation rel,
          AlterTableCmd *cmd, LOCKMODE lockmode);
static void ATRewriteTables(List **wqueue, LOCKMODE lockmode);
static void ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode);
static AlteredTableInfo *ATGetQueueEntry(List **wqueue, Relation rel);
static void ATSimplePermissions(Relation rel, int allowed_targets);
static void ATWrongRelkindError(Relation rel, int allowed_targets);
static void ATSimpleRecursion(List **wqueue, Relation rel,
                  AlterTableCmd *cmd, bool recurse, LOCKMODE lockmode);
static void ATTypedTableRecursion(List **wqueue, Relation rel, AlterTableCmd *cmd,
                      LOCKMODE lockmode);
static List *find_typed_table_dependencies(Oid typeOid, const char *typeName,
                              DropBehavior behavior);
static void ATPrepAddColumn(List **wqueue, Relation rel, bool recurse, bool recursing,
                AlterTableCmd *cmd, LOCKMODE lockmode);
static void ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
                ColumnDef *colDef, bool isOid,
                bool recurse, bool recursing, LOCKMODE lockmode);
static void check_for_column_name_collision(Relation rel, const char *colname);
static void add_column_datatype_dependency(Oid relid, int32 attnum, Oid typid);
static void add_column_collation_dependency(Oid relid, int32 attnum, Oid collid);
static void ATPrepAddOids(List **wqueue, Relation rel, bool recurse,
              AlterTableCmd *cmd, LOCKMODE lockmode);
static void ATExecDropNotNull(Relation rel, const char *colName, LOCKMODE lockmode);
static void ATExecSetNotNull(AlteredTableInfo *tab, Relation rel,
                 const char *colName, LOCKMODE lockmode);
static void ATExecColumnDefault(Relation rel, const char *colName,
                    Node *newDefault, LOCKMODE lockmode);
static void ATPrepSetStatistics(Relation rel, const char *colName,
                    Node *newValue, LOCKMODE lockmode);
static void ATExecSetStatistics(Relation rel, const char *colName,
                    Node *newValue, LOCKMODE lockmode);
static void ATExecSetOptions(Relation rel, const char *colName,
                 Node *options, bool isReset, LOCKMODE lockmode);
static void ATExecSetStorage(Relation rel, const char *colName,
                 Node *newValue, LOCKMODE lockmode);
static void ATPrepDropColumn(List **wqueue, Relation rel, bool recurse, bool recursing,
                 AlterTableCmd *cmd, LOCKMODE lockmode);
static void ATExecDropColumn(List **wqueue, Relation rel, const char *colName,
                 DropBehavior behavior,
                 bool recurse, bool recursing,
                 bool missing_ok, LOCKMODE lockmode);
static void ATExecAddIndex(AlteredTableInfo *tab, Relation rel,
               IndexStmt *stmt, bool is_rebuild, LOCKMODE lockmode);
static void ATExecAddConstraint(List **wqueue,
                    AlteredTableInfo *tab, Relation rel,
                    Constraint *newConstraint, bool recurse, bool is_readd,
                    LOCKMODE lockmode);
static void ATExecAddIndexConstraint(AlteredTableInfo *tab, Relation rel,
                         IndexStmt *stmt, LOCKMODE lockmode);
static void ATAddCheckConstraint(List **wqueue,
                     AlteredTableInfo *tab, Relation rel,
                     Constraint *constr,
                     bool recurse, bool recursing, bool is_readd,
                     LOCKMODE lockmode);
static void ATAddForeignKeyConstraint(AlteredTableInfo *tab, Relation rel,
                          Constraint *fkconstraint, LOCKMODE lockmode);
static void ATExecDropConstraint(Relation rel, const char *constrName,
                     DropBehavior behavior,
                     bool recurse, bool recursing,
                     bool missing_ok, LOCKMODE lockmode);
static void ATPrepAlterColumnType(List **wqueue,
                      AlteredTableInfo *tab, Relation rel,
                      bool recurse, bool recursing,
                      AlterTableCmd *cmd, LOCKMODE lockmode);
static bool ATColumnChangeRequiresRewrite(Node *expr, AttrNumber varattno);
static void ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
                      AlterTableCmd *cmd, LOCKMODE lockmode);
static void ATExecAlterColumnGenericOptions(Relation rel, const char *colName,
                                List *options, LOCKMODE lockmode);
static void ATPostAlterTypeCleanup(List **wqueue, AlteredTableInfo *tab, LOCKMODE lockmode);
static void ATPostAlterTypeParse(Oid oldId, char *cmd,
                     List **wqueue, LOCKMODE lockmode, bool rewrite);
static void TryReuseIndex(Oid oldId, IndexStmt *stmt);
static void TryReuseForeignKey(Oid oldId, Constraint *con);
static void change_owner_fix_column_acls(Oid relationOid,
                             Oid oldOwnerId, Oid newOwnerId);
static void change_owner_recurse_to_sequences(Oid relationOid,
                                  Oid newOwnerId, LOCKMODE lockmode);
static void ATExecClusterOn(Relation rel, const char *indexName, LOCKMODE lockmode);
static void ATExecDropCluster(Relation rel, LOCKMODE lockmode);
static void ATPrepSetTableSpace(AlteredTableInfo *tab, Relation rel,
                    char *tablespacename, LOCKMODE lockmode);
static void ATExecSetTableSpace(Oid tableOid, Oid newTableSpace, LOCKMODE lockmode);
static void ATExecSetRelOptions(Relation rel, List *defList,
                    AlterTableType operation,
                    LOCKMODE lockmode);
static void ATExecEnableDisableTrigger(Relation rel, char *trigname,
                       char fires_when, bool skip_system, LOCKMODE lockmode);
static void ATExecEnableDisableRule(Relation rel, char *rulename,
                        char fires_when, LOCKMODE lockmode);
static void ATPrepAddInherit(Relation child_rel);
static void ATExecAddInherit(Relation child_rel, RangeVar *parent, LOCKMODE lockmode);
static void ATExecDropInherit(Relation rel, RangeVar *parent, LOCKMODE lockmode);
static void drop_parent_dependency(Oid relid, Oid refclassid, Oid refobjid);
static void ATExecAddOf(Relation rel, const TypeName *ofTypename, LOCKMODE lockmode);
static void ATExecDropOf(Relation rel, LOCKMODE lockmode);
static void ATExecGenericOptions(Relation rel, List *options);

static void copy_relation_data(SMgrRelation rel, SMgrRelation dst,
                   ForkNumber forkNum, char relpersistence);
static const char *storage_name(char c);

static void RangeVarCallbackForDropRelation(const RangeVar *rel, Oid relOid,
                                Oid oldRelOid, void *arg);
static void RangeVarCallbackForAlterRelation(const RangeVar *rv, Oid relid,
                                 Oid oldrelid, void *arg);


/* ----------------------------------------------------------------
 *      DefineRelation
 *              Creates a new relation.
 *
 * stmt carries parsetree information from an ordinary CREATE TABLE statement.
 * The other arguments are used to extend the behavior for other cases:
 * relkind: relkind to assign to the new relation
 * ownerId: if not InvalidOid, use this as the new relation's owner.
 *
 * Note that permissions checks are done against current user regardless of
 * ownerId.  A nonzero ownerId is used when someone is creating a relation
 * "on behalf of" someone else, so we still want to see that the current user
 * has permissions to do it.
 *
 * If successful, returns the OID of the new relation.
 * ----------------------------------------------------------------
 */
Oid
DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId)
{
    char        relname[NAMEDATALEN];
    Oid         namespaceId;
    List       *schema = stmt->tableElts;
    Oid         relationId;
    Oid         tablespaceId;
    Relation    rel;
    TupleDesc   descriptor;
    List       *inheritOids;
    List       *old_constraints;
    bool        localHasOids;
    int         parentOidCount;
    List       *rawDefaults;
    List       *cookedDefaults;
    Datum       reloptions;
    ListCell   *listptr;
    AttrNumber  attnum;
    static char *validnsps[] = HEAP_RELOPT_NAMESPACES;
    Oid         ofTypeId;

    /*
     * Truncate relname to appropriate length (probably a waste of time, as
     * parser should have done this already).
     */
    StrNCpy(relname, stmt->relation->relname, NAMEDATALEN);

    /*
     * Check consistency of arguments
     */
    if (stmt->oncommit != ONCOMMIT_NOOP
        && stmt->relation->relpersistence != RELPERSISTENCE_TEMP)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                 errmsg("ON COMMIT can only be used on temporary tables")));
    if (stmt->constraints != NIL && relkind == RELKIND_FOREIGN_TABLE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("constraints are not supported on foreign tables")));

    /*
     * Look up the namespace in which we are supposed to create the relation,
     * check we have permission to create there, lock it against concurrent
     * drop, and mark stmt->relation as RELPERSISTENCE_TEMP if a temporary
     * namespace is selected.
     */
    namespaceId =
        RangeVarGetAndCheckCreationNamespace(stmt->relation, NoLock, NULL);

    /*
     * Security check: disallow creating temp tables from security-restricted
     * code.  This is needed because calling code might not expect untrusted
     * tables to appear in pg_temp at the front of its search path.
     */
    if (stmt->relation->relpersistence == RELPERSISTENCE_TEMP
        && InSecurityRestrictedOperation())
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("cannot create temporary table within security-restricted operation")));

    /*
     * Select tablespace to use.  If not specified, use default tablespace
     * (which may in turn default to database's default).
     */
    if (stmt->tablespacename)
    {
        tablespaceId = get_tablespace_oid(stmt->tablespacename, false);
    }
    else
    {
        tablespaceId = GetDefaultTablespace(stmt->relation->relpersistence);
        /* note InvalidOid is OK in this case */
    }

    /* Check permissions except when using database's default */
    if (OidIsValid(tablespaceId) && tablespaceId != MyDatabaseTableSpace)
    {
        AclResult   aclresult;

        aclresult = pg_tablespace_aclcheck(tablespaceId, GetUserId(),
                                           ACL_CREATE);
        if (aclresult != ACLCHECK_OK)
            aclcheck_error(aclresult, ACL_KIND_TABLESPACE,
                           get_tablespace_name(tablespaceId));
    }

    /* In all cases disallow placing user relations in pg_global */
    if (tablespaceId == GLOBALTABLESPACE_OID)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("only shared relations can be placed in pg_global tablespace")));

    /* Identify user ID that will own the table */
    if (!OidIsValid(ownerId))
        ownerId = GetUserId();

    /*
     * Parse and validate reloptions, if any.
     */
    reloptions = transformRelOptions((Datum) 0, stmt->options, NULL, validnsps,
                                     true, false);

    (void) heap_reloptions(relkind, reloptions, true);

    if (stmt->ofTypename)
    {
        AclResult   aclresult;

        ofTypeId = typenameTypeId(NULL, stmt->ofTypename);

        aclresult = pg_type_aclcheck(ofTypeId, GetUserId(), ACL_USAGE);
        if (aclresult != ACLCHECK_OK)
            aclcheck_error_type(aclresult, ofTypeId);
    }
    else
        ofTypeId = InvalidOid;

    /*
     * Look up inheritance ancestors and generate relation schema, including
     * inherited attributes.
     */
    schema = MergeAttributes(schema, stmt->inhRelations,
                             stmt->relation->relpersistence,
                             &inheritOids, &old_constraints, &parentOidCount);

    /*
     * Create a tuple descriptor from the relation schema.  Note that this
     * deals with column names, types, and NOT NULL constraints, but not
     * default values or CHECK constraints; we handle those below.
     */
    descriptor = BuildDescForRelation(schema);

    localHasOids = interpretOidsOption(stmt->options,
                                       (relkind == RELKIND_RELATION ||
                                        relkind == RELKIND_FOREIGN_TABLE));
    descriptor->tdhasoid = (localHasOids || parentOidCount > 0);

    /*
     * Find columns with default values and prepare for insertion of the
     * defaults.  Pre-cooked (that is, inherited) defaults go into a list of
     * CookedConstraint structs that we'll pass to heap_create_with_catalog,
     * while raw defaults go into a list of RawColumnDefault structs that will
     * be processed by AddRelationNewConstraints.  (We can't deal with raw
     * expressions until we can do transformExpr.)
     *
     * We can set the atthasdef flags now in the tuple descriptor; this just
     * saves StoreAttrDefault from having to do an immediate update of the
     * pg_attribute rows.
     */
    rawDefaults = NIL;
    cookedDefaults = NIL;
    attnum = 0;

    foreach(listptr, schema)
    {
        ColumnDef  *colDef = lfirst(listptr);

        attnum++;

        if (colDef->raw_default != NULL)
        {
            RawColumnDefault *rawEnt;

            Assert(colDef->cooked_default == NULL);

            rawEnt = (RawColumnDefault *) palloc(sizeof(RawColumnDefault));
            rawEnt->attnum = attnum;
            rawEnt->raw_default = colDef->raw_default;
            rawDefaults = lappend(rawDefaults, rawEnt);
            descriptor->attrs[attnum - 1]->atthasdef = true;
        }
        else if (colDef->cooked_default != NULL)
        {
            CookedConstraint *cooked;

            cooked = (CookedConstraint *) palloc(sizeof(CookedConstraint));
            cooked->contype = CONSTR_DEFAULT;
            cooked->name = NULL;
            cooked->attnum = attnum;
            cooked->expr = colDef->cooked_default;
            cooked->skip_validation = false;
            cooked->is_local = true;    /* not used for defaults */
            cooked->inhcount = 0;       /* ditto */
            cooked->is_no_inherit = false;
            cookedDefaults = lappend(cookedDefaults, cooked);
            descriptor->attrs[attnum - 1]->atthasdef = true;
        }
    }

    /*
     * Create the relation.  Inherited defaults and constraints are passed in
     * for immediate handling --- since they don't need parsing, they can be
     * stored immediately.
     */
    relationId = heap_create_with_catalog(relname,
                                          namespaceId,
                                          tablespaceId,
                                          InvalidOid,
                                          InvalidOid,
                                          ofTypeId,
                                          ownerId,
                                          descriptor,
                                          list_concat(cookedDefaults,
                                                      old_constraints),
                                          relkind,
                                          stmt->relation->relpersistence,
                                          false,
                                          false,
                                          localHasOids,
                                          parentOidCount,
                                          stmt->oncommit,
                                          reloptions,
                                          true,
                                          allowSystemTableMods,
                                          false);

    /* Store inheritance information for new rel. */
    StoreCatalogInheritance(relationId, inheritOids);

    /*
     * We must bump the command counter to make the newly-created relation
     * tuple visible for opening.
     */
    CommandCounterIncrement();

    /*
     * Open the new relation and acquire exclusive lock on it.  This isn't
     * really necessary for locking out other backends (since they can't see
     * the new rel anyway until we commit), but it keeps the lock manager from
     * complaining about deadlock risks.
     */
    rel = relation_open(relationId, AccessExclusiveLock);

    /*
     * Now add any newly specified column default values and CHECK constraints
     * to the new relation.  These are passed to us in the form of raw
     * parsetrees; we need to transform them to executable expression trees
     * before they can be added. The most convenient way to do that is to
     * apply the parser's transformExpr routine, but transformExpr doesn't
     * work unless we have a pre-existing relation. So, the transformation has
     * to be postponed to this final step of CREATE TABLE.
     */
    if (rawDefaults || stmt->constraints)
        AddRelationNewConstraints(rel, rawDefaults, stmt->constraints,
                                  true, true, false);

    /*
     * Clean up.  We keep lock on new relation (although it shouldn't be
     * visible to anyone else anyway, until commit).
     */
    relation_close(rel, NoLock);

    return relationId;
}

/*
 * Emit the right error or warning message for a "DROP" command issued on a
 * non-existent relation
 */
static void
DropErrorMsgNonExistent(const char *relname, char rightkind, bool missing_ok)
{
    const struct dropmsgstrings *rentry;

    for (rentry = dropmsgstringarray; rentry->kind != '\0'; rentry++)
    {
        if (rentry->kind == rightkind)
        {
            if (!missing_ok)
            {
                ereport(ERROR,
                        (errcode(rentry->nonexistent_code),
                         errmsg(rentry->nonexistent_msg, relname)));
            }
            else
            {
                ereport(NOTICE, (errmsg(rentry->skipping_msg, relname)));
                break;
            }
        }
    }

    Assert(rentry->kind != '\0');       /* Should be impossible */
}

/*
 * Emit the right error message for a "DROP" command issued on a
 * relation of the wrong type
 */
static void
DropErrorMsgWrongType(const char *relname, char wrongkind, char rightkind)
{
    const struct dropmsgstrings *rentry;
    const struct dropmsgstrings *wentry;

    for (rentry = dropmsgstringarray; rentry->kind != '\0'; rentry++)
        if (rentry->kind == rightkind)
            break;
    Assert(rentry->kind != '\0');

    for (wentry = dropmsgstringarray; wentry->kind != '\0'; wentry++)
        if (wentry->kind == wrongkind)
            break;
    /* wrongkind could be something we don't have in our table... */

    ereport(ERROR,
            (errcode(ERRCODE_WRONG_OBJECT_TYPE),
             errmsg(rentry->nota_msg, relname),
       (wentry->kind != '\0') ? errhint("%s", _(wentry->drophint_msg)) : 0));
}

/*
 * RemoveRelations
 *      Implements DROP TABLE, DROP INDEX, DROP SEQUENCE, DROP VIEW,
 *      DROP MATERIALIZED VIEW, DROP FOREIGN TABLE
 */
void
RemoveRelations(DropStmt *drop)
{
    ObjectAddresses *objects;
    char        relkind;
    ListCell   *cell;
    int         flags = 0;
    LOCKMODE    lockmode = AccessExclusiveLock;

    /* DROP CONCURRENTLY uses a weaker lock, and has some restrictions */
    if (drop->concurrent)
    {
        flags |= PERFORM_DELETION_CONCURRENTLY;
        lockmode = ShareUpdateExclusiveLock;
        Assert(drop->removeType == OBJECT_INDEX);
        if (list_length(drop->objects) != 1)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                     errmsg("DROP INDEX CONCURRENTLY does not support dropping multiple objects")));
        if (drop->behavior == DROP_CASCADE)
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                errmsg("DROP INDEX CONCURRENTLY does not support CASCADE")));
    }

    /*
     * First we identify all the relations, then we delete them in a single
     * performMultipleDeletions() call.  This is to avoid unwanted DROP
     * RESTRICT errors if one of the relations depends on another.
     */

    /* Determine required relkind */
    switch (drop->removeType)
    {
        case OBJECT_TABLE:
            relkind = RELKIND_RELATION;
            break;

        case OBJECT_INDEX:
            relkind = RELKIND_INDEX;
            break;

        case OBJECT_SEQUENCE:
            relkind = RELKIND_SEQUENCE;
            break;

        case OBJECT_VIEW:
            relkind = RELKIND_VIEW;
            break;

        case OBJECT_MATVIEW:
            relkind = RELKIND_MATVIEW;
            break;

        case OBJECT_FOREIGN_TABLE:
            relkind = RELKIND_FOREIGN_TABLE;
            break;

        default:
            elog(ERROR, "unrecognized drop object type: %d",
                 (int) drop->removeType);
            relkind = 0;        /* keep compiler quiet */
            break;
    }

    /* Lock and validate each relation; build a list of object addresses */
    objects = new_object_addresses();

    foreach(cell, drop->objects)
    {
        RangeVar   *rel = makeRangeVarFromNameList((List *) lfirst(cell));
        Oid         relOid;
        ObjectAddress obj;
        struct DropRelationCallbackState state;

        /*
         * These next few steps are a great deal like relation_openrv, but we
         * don't bother building a relcache entry since we don't need it.
         *
         * Check for shared-cache-inval messages before trying to access the
         * relation.  This is needed to cover the case where the name
         * identifies a rel that has been dropped and recreated since the
         * start of our transaction: if we don't flush the old syscache entry,
         * then we'll latch onto that entry and suffer an error later.
         */
        AcceptInvalidationMessages();

        /* Look up the appropriate relation using namespace search. */
        state.relkind = relkind;
        state.heapOid = InvalidOid;
        state.concurrent = drop->concurrent;
        relOid = RangeVarGetRelidExtended(rel, lockmode, true,
                                          false,
                                          RangeVarCallbackForDropRelation,
                                          (void *) &state);

        /* Not there? */
        if (!OidIsValid(relOid))
        {
            DropErrorMsgNonExistent(rel->relname, relkind, drop->missing_ok);
            continue;
        }

        /* OK, we're ready to delete this one */
        obj.classId = RelationRelationId;
        obj.objectId = relOid;
        obj.objectSubId = 0;

        add_exact_object_address(&obj, objects);
    }

    performMultipleDeletions(objects, drop->behavior, flags);

    free_object_addresses(objects);
}

/*
 * Before acquiring a table lock, check whether we have sufficient rights.
 * In the case of DROP INDEX, also try to lock the table before the index.
 */
static void
RangeVarCallbackForDropRelation(const RangeVar *rel, Oid relOid, Oid oldRelOid,
                                void *arg)
{
    HeapTuple   tuple;
    struct DropRelationCallbackState *state;
    char        relkind;
    Form_pg_class classform;
    LOCKMODE    heap_lockmode;

    state = (struct DropRelationCallbackState *) arg;
    relkind = state->relkind;
    heap_lockmode = state->concurrent ?
        ShareUpdateExclusiveLock : AccessExclusiveLock;

    /*
     * If we previously locked some other index's heap, and the name we're
     * looking up no longer refers to that relation, release the now-useless
     * lock.
     */
    if (relOid != oldRelOid && OidIsValid(state->heapOid))
    {
        UnlockRelationOid(state->heapOid, heap_lockmode);
        state->heapOid = InvalidOid;
    }

    /* Didn't find a relation, so no need for locking or permission checks. */
    if (!OidIsValid(relOid))
        return;

    tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relOid));
    if (!HeapTupleIsValid(tuple))
        return;                 /* concurrently dropped, so nothing to do */
    classform = (Form_pg_class) GETSTRUCT(tuple);

    if (classform->relkind != relkind)
        DropErrorMsgWrongType(rel->relname, classform->relkind, relkind);

    /* Allow DROP to either table owner or schema owner */
    if (!pg_class_ownercheck(relOid, GetUserId()) &&
        !pg_namespace_ownercheck(classform->relnamespace, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
                       rel->relname);

    if (!allowSystemTableMods && IsSystemClass(classform))
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied: \"%s\" is a system catalog",
                        rel->relname)));

    ReleaseSysCache(tuple);

    /*
     * In DROP INDEX, attempt to acquire lock on the parent table before
     * locking the index.  index_drop() will need this anyway, and since
     * regular queries lock tables before their indexes, we risk deadlock if
     * we do it the other way around.  No error if we don't find a pg_index
     * entry, though --- the relation may have been dropped.
     */
    if (relkind == RELKIND_INDEX && relOid != oldRelOid)
    {
        state->heapOid = IndexGetRelation(relOid, true);
        if (OidIsValid(state->heapOid))
            LockRelationOid(state->heapOid, heap_lockmode);
    }
}

/*
 * ExecuteTruncate
 *      Executes a TRUNCATE command.
 *
 * This is a multi-relation truncate.  We first open and grab exclusive
 * lock on all relations involved, checking permissions and otherwise
 * verifying that the relation is OK for truncation.  In CASCADE mode,
 * relations having FK references to the targeted relations are automatically
 * added to the group; in RESTRICT mode, we check that all FK references are
 * internal to the group that's being truncated.  Finally all the relations
 * are truncated and reindexed.
 */
void
ExecuteTruncate(TruncateStmt *stmt)
{
    List       *rels = NIL;
    List       *relids = NIL;
    List       *seq_relids = NIL;
    EState     *estate;
    ResultRelInfo *resultRelInfos;
    ResultRelInfo *resultRelInfo;
    SubTransactionId mySubid;
    ListCell   *cell;

    /*
     * Open, exclusive-lock, and check all the explicitly-specified relations
     */
    foreach(cell, stmt->relations)
    {
        RangeVar   *rv = lfirst(cell);
        Relation    rel;
        bool        recurse = interpretInhOption(rv->inhOpt);
        Oid         myrelid;

        rel = heap_openrv(rv, AccessExclusiveLock);
        myrelid = RelationGetRelid(rel);
        /* don't throw error for "TRUNCATE foo, foo" */
        if (list_member_oid(relids, myrelid))
        {
            heap_close(rel, AccessExclusiveLock);
            continue;
        }
        truncate_check_rel(rel);
        rels = lappend(rels, rel);
        relids = lappend_oid(relids, myrelid);

        if (recurse)
        {
            ListCell   *child;
            List       *children;

            children = find_all_inheritors(myrelid, AccessExclusiveLock, NULL);

            foreach(child, children)
            {
                Oid         childrelid = lfirst_oid(child);

                if (list_member_oid(relids, childrelid))
                    continue;

                /* find_all_inheritors already got lock */
                rel = heap_open(childrelid, NoLock);
                truncate_check_rel(rel);
                rels = lappend(rels, rel);
                relids = lappend_oid(relids, childrelid);
            }
        }
    }

    /*
     * In CASCADE mode, suck in all referencing relations as well.  This
     * requires multiple iterations to find indirectly-dependent relations. At
     * each phase, we need to exclusive-lock new rels before looking for their
     * dependencies, else we might miss something.  Also, we check each rel as
     * soon as we open it, to avoid a faux pas such as holding lock for a long
     * time on a rel we have no permissions for.
     */
    if (stmt->behavior == DROP_CASCADE)
    {
        for (;;)
        {
            List       *newrelids;

            newrelids = heap_truncate_find_FKs(relids);
            if (newrelids == NIL)
                break;          /* nothing else to add */

            foreach(cell, newrelids)
            {
                Oid         relid = lfirst_oid(cell);
                Relation    rel;

                rel = heap_open(relid, AccessExclusiveLock);
                ereport(NOTICE,
                        (errmsg("truncate cascades to table \"%s\"",
                                RelationGetRelationName(rel))));
                truncate_check_rel(rel);
                rels = lappend(rels, rel);
                relids = lappend_oid(relids, relid);
            }
        }
    }

    /*
     * Check foreign key references.  In CASCADE mode, this should be
     * unnecessary since we just pulled in all the references; but as a
     * cross-check, do it anyway if in an Assert-enabled build.
     */
#ifdef USE_ASSERT_CHECKING
    heap_truncate_check_FKs(rels, false);
#else
    if (stmt->behavior == DROP_RESTRICT)
        heap_truncate_check_FKs(rels, false);
#endif

    /*
     * If we are asked to restart sequences, find all the sequences, lock them
     * (we need AccessExclusiveLock for ResetSequence), and check permissions.
     * We want to do this early since it's pointless to do all the truncation
     * work only to fail on sequence permissions.
     */
    if (stmt->restart_seqs)
    {
        foreach(cell, rels)
        {
            Relation    rel = (Relation) lfirst(cell);
            List       *seqlist = getOwnedSequences(RelationGetRelid(rel));
            ListCell   *seqcell;

            foreach(seqcell, seqlist)
            {
                Oid         seq_relid = lfirst_oid(seqcell);
                Relation    seq_rel;

                seq_rel = relation_open(seq_relid, AccessExclusiveLock);

                /* This check must match AlterSequence! */
                if (!pg_class_ownercheck(seq_relid, GetUserId()))
                    aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
                                   RelationGetRelationName(seq_rel));

                seq_relids = lappend_oid(seq_relids, seq_relid);

                relation_close(seq_rel, NoLock);
            }
        }
    }

    /* Prepare to catch AFTER triggers. */
    AfterTriggerBeginQuery();

    /*
     * To fire triggers, we'll need an EState as well as a ResultRelInfo for
     * each relation.  We don't need to call ExecOpenIndices, though.
     */
    estate = CreateExecutorState();
    resultRelInfos = (ResultRelInfo *)
        palloc(list_length(rels) * sizeof(ResultRelInfo));
    resultRelInfo = resultRelInfos;
    foreach(cell, rels)
    {
        Relation    rel = (Relation) lfirst(cell);

        InitResultRelInfo(resultRelInfo,
                          rel,
                          0,    /* dummy rangetable index */
                          0);
        resultRelInfo++;
    }
    estate->es_result_relations = resultRelInfos;
    estate->es_num_result_relations = list_length(rels);

    /*
     * Process all BEFORE STATEMENT TRUNCATE triggers before we begin
     * truncating (this is because one of them might throw an error). Also, if
     * we were to allow them to prevent statement execution, that would need
     * to be handled here.
     */
    resultRelInfo = resultRelInfos;
    foreach(cell, rels)
    {
        estate->es_result_relation_info = resultRelInfo;
        ExecBSTruncateTriggers(estate, resultRelInfo);
        resultRelInfo++;
    }

    /*
     * OK, truncate each table.
     */
    mySubid = GetCurrentSubTransactionId();

    foreach(cell, rels)
    {
        Relation    rel = (Relation) lfirst(cell);

        /*
         * Normally, we need a transaction-safe truncation here.  However, if
         * the table was either created in the current (sub)transaction or has
         * a new relfilenode in the current (sub)transaction, then we can just
         * truncate it in-place, because a rollback would cause the whole
         * table or the current physical file to be thrown away anyway.
         */
        if (rel->rd_createSubid == mySubid ||
            rel->rd_newRelfilenodeSubid == mySubid)
        {
            /* Immediate, non-rollbackable truncation is OK */
            heap_truncate_one_rel(rel);
        }
        else
        {
            Oid         heap_relid;
            Oid         toast_relid;
            MultiXactId minmulti;

            /*
             * This effectively deletes all rows in the table, and may be done
             * in a serializable transaction.  In that case we must record a
             * rw-conflict in to this transaction from each transaction
             * holding a predicate lock on the table.
             */
            CheckTableForSerializableConflictIn(rel);

            minmulti = GetOldestMultiXactId();

            /*
             * Need the full transaction-safe pushups.
             *
             * Create a new empty storage file for the relation, and assign it
             * as the relfilenode value. The old storage file is scheduled for
             * deletion at commit.
             */
            RelationSetNewRelfilenode(rel, RecentXmin, minmulti);
            if (rel->rd_rel->relpersistence == RELPERSISTENCE_UNLOGGED)
                heap_create_init_fork(rel);

            heap_relid = RelationGetRelid(rel);
            toast_relid = rel->rd_rel->reltoastrelid;

            /*
             * The same for the toast table, if any.
             */
            if (OidIsValid(toast_relid))
            {
                rel = relation_open(toast_relid, AccessExclusiveLock);
                RelationSetNewRelfilenode(rel, RecentXmin, minmulti);
                if (rel->rd_rel->relpersistence == RELPERSISTENCE_UNLOGGED)
                    heap_create_init_fork(rel);
                heap_close(rel, NoLock);
            }

            /*
             * Reconstruct the indexes to match, and we're done.
             */
            reindex_relation(heap_relid, REINDEX_REL_PROCESS_TOAST);
        }
    }

    /*
     * Restart owned sequences if we were asked to.
     */
    foreach(cell, seq_relids)
    {
        Oid         seq_relid = lfirst_oid(cell);

        ResetSequence(seq_relid);
    }

    /*
     * Process all AFTER STATEMENT TRUNCATE triggers.
     */
    resultRelInfo = resultRelInfos;
    foreach(cell, rels)
    {
        estate->es_result_relation_info = resultRelInfo;
        ExecASTruncateTriggers(estate, resultRelInfo);
        resultRelInfo++;
    }

    /* Handle queued AFTER triggers */
    AfterTriggerEndQuery(estate);

    /* We can clean up the EState now */
    FreeExecutorState(estate);

    /* And close the rels (can't do this while EState still holds refs) */
    foreach(cell, rels)
    {
        Relation    rel = (Relation) lfirst(cell);

        heap_close(rel, NoLock);
    }
}

/*
 * Check that a given rel is safe to truncate.  Subroutine for ExecuteTruncate
 */
static void
truncate_check_rel(Relation rel)
{
    AclResult   aclresult;

    /* Only allow truncate on regular tables */
    if (rel->rd_rel->relkind != RELKIND_RELATION)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not a table",
                        RelationGetRelationName(rel))));

    /* Permissions checks */
    aclresult = pg_class_aclcheck(RelationGetRelid(rel), GetUserId(),
                                  ACL_TRUNCATE);
    if (aclresult != ACLCHECK_OK)
        aclcheck_error(aclresult, ACL_KIND_CLASS,
                       RelationGetRelationName(rel));

    if (!allowSystemTableMods && IsSystemRelation(rel))
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied: \"%s\" is a system catalog",
                        RelationGetRelationName(rel))));

    /*
     * Don't allow truncate on temp tables of other backends ... their local
     * buffer manager is not going to cope.
     */
    if (RELATION_IS_OTHER_TEMP(rel))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
              errmsg("cannot truncate temporary tables of other sessions")));

    /*
     * Also check for active uses of the relation in the current transaction,
     * including open scans and pending AFTER trigger events.
     */
    CheckTableNotInUse(rel, "TRUNCATE");
}

/*
 * storage_name
 *    returns the name corresponding to a typstorage/attstorage enum value
 */
static const char *
storage_name(char c)
{
    switch (c)
    {
        case 'p':
            return "PLAIN";
        case 'm':
            return "MAIN";
        case 'x':
            return "EXTENDED";
        case 'e':
            return "EXTERNAL";
        default:
            return "???";
    }
}

/*----------
 * MergeAttributes
 *      Returns new schema given initial schema and superclasses.
 *
 * Input arguments:
 * 'schema' is the column/attribute definition for the table. (It's a list
 *      of ColumnDef's.) It is destructively changed.
 * 'supers' is a list of names (as RangeVar nodes) of parent relations.
 * 'relpersistence' is a persistence type of the table.
 *
 * Output arguments:
 * 'supOids' receives a list of the OIDs of the parent relations.
 * 'supconstr' receives a list of constraints belonging to the parents,
 *      updated as necessary to be valid for the child.
 * 'supOidCount' is set to the number of parents that have OID columns.
 *
 * Return value:
 * Completed schema list.
 *
 * Notes:
 *    The order in which the attributes are inherited is very important.
 *    Intuitively, the inherited attributes should come first. If a table
 *    inherits from multiple parents, the order of those attributes are
 *    according to the order of the parents specified in CREATE TABLE.
 *
 *    Here's an example:
 *
 *      create table person (name text, age int4, location point);
 *      create table emp (salary int4, manager text) inherits(person);
 *      create table student (gpa float8) inherits (person);
 *      create table stud_emp (percent int4) inherits (emp, student);
 *
 *    The order of the attributes of stud_emp is:
 *
 *                          person {1:name, 2:age, 3:location}
 *                          /    \
 *             {6:gpa}  student   emp {4:salary, 5:manager}
 *                          \    /
 *                         stud_emp {7:percent}
 *
 *     If the same attribute name appears multiple times, then it appears
 *     in the result table in the proper location for its first appearance.
 *
 *     Constraints (including NOT NULL constraints) for the child table
 *     are the union of all relevant constraints, from both the child schema
 *     and parent tables.
 *
 *     The default value for a child column is defined as:
 *      (1) If the child schema specifies a default, that value is used.
 *      (2) If neither the child nor any parent specifies a default, then
 *          the column will not have a default.
 *      (3) If conflicting defaults are inherited from different parents
 *          (and not overridden by the child), an error is raised.
 *      (4) Otherwise the inherited default is used.
 *      Rule (3) is new in Postgres 7.1; in earlier releases you got a
 *      rather arbitrary choice of which parent default to use.
 *----------
 */
static List *
MergeAttributes(List *schema, List *supers, char relpersistence,
                List **supOids, List **supconstr, int *supOidCount)
{
    ListCell   *entry;
    List       *inhSchema = NIL;
    List       *parentOids = NIL;
    List       *constraints = NIL;
    int         parentsWithOids = 0;
    bool        have_bogus_defaults = false;
    int         child_attno;
    static Node bogus_marker = {0};     /* marks conflicting defaults */

    /*
     * Check for and reject tables with too many columns. We perform this
     * check relatively early for two reasons: (a) we don't run the risk of
     * overflowing an AttrNumber in subsequent code (b) an O(n^2) algorithm is
     * okay if we're processing <= 1600 columns, but could take minutes to
     * execute if the user attempts to create a table with hundreds of
     * thousands of columns.
     *
     * Note that we also need to check that any we do not exceed this figure
     * after including columns from inherited relations.
     */
    if (list_length(schema) > MaxHeapAttributeNumber)
        ereport(ERROR,
                (errcode(ERRCODE_TOO_MANY_COLUMNS),
                 errmsg("tables can have at most %d columns",
                        MaxHeapAttributeNumber)));

    /*
     * Check for duplicate names in the explicit list of attributes.
     *
     * Although we might consider merging such entries in the same way that we
     * handle name conflicts for inherited attributes, it seems to make more
     * sense to assume such conflicts are errors.
     */
    foreach(entry, schema)
    {
        ColumnDef  *coldef = lfirst(entry);
        ListCell   *rest = lnext(entry);
        ListCell   *prev = entry;

        if (coldef->typeName == NULL)

            /*
             * Typed table column option that does not belong to a column from
             * the type.  This works because the columns from the type come
             * first in the list.
             */
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_COLUMN),
                     errmsg("column \"%s\" does not exist",
                            coldef->colname)));

        while (rest != NULL)
        {
            ColumnDef  *restdef = lfirst(rest);
            ListCell   *next = lnext(rest);     /* need to save it in case we
                                                 * delete it */

            if (strcmp(coldef->colname, restdef->colname) == 0)
            {
                if (coldef->is_from_type)
                {
                    /*
                     * merge the column options into the column from the type
                     */
                    coldef->is_not_null = restdef->is_not_null;
                    coldef->raw_default = restdef->raw_default;
                    coldef->cooked_default = restdef->cooked_default;
                    coldef->constraints = restdef->constraints;
                    coldef->is_from_type = false;
                    list_delete_cell(schema, rest, prev);
                }
                else
                    ereport(ERROR,
                            (errcode(ERRCODE_DUPLICATE_COLUMN),
                             errmsg("column \"%s\" specified more than once",
                                    coldef->colname)));
            }
            prev = rest;
            rest = next;
        }
    }

    /*
     * Scan the parents left-to-right, and merge their attributes to form a
     * list of inherited attributes (inhSchema).  Also check to see if we need
     * to inherit an OID column.
     */
    child_attno = 0;
    foreach(entry, supers)
    {
        RangeVar   *parent = (RangeVar *) lfirst(entry);
        Relation    relation;
        TupleDesc   tupleDesc;
        TupleConstr *constr;
        AttrNumber *newattno;
        AttrNumber  parent_attno;

        /*
         * A self-exclusive lock is needed here.  If two backends attempt to
         * add children to the same parent simultaneously, and that parent has
         * no pre-existing children, then both will attempt to update the
         * parent's relhassubclass field, leading to a "tuple concurrently
         * updated" error.  Also, this interlocks against a concurrent ANALYZE
         * on the parent table, which might otherwise be attempting to clear
         * the parent's relhassubclass field, if its previous children were
         * recently dropped.
         */
        relation = heap_openrv(parent, ShareUpdateExclusiveLock);

        if (relation->rd_rel->relkind != RELKIND_RELATION)
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                     errmsg("inherited relation \"%s\" is not a table",
                            parent->relname)));
        /* Permanent rels cannot inherit from temporary ones */
        if (relpersistence != RELPERSISTENCE_TEMP &&
            relation->rd_rel->relpersistence == RELPERSISTENCE_TEMP)
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                     errmsg("cannot inherit from temporary relation \"%s\"",
                            parent->relname)));

        /* If existing rel is temp, it must belong to this session */
        if (relation->rd_rel->relpersistence == RELPERSISTENCE_TEMP &&
            !relation->rd_islocaltemp)
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                     errmsg("cannot inherit from temporary relation of another session")));

        /*
         * We should have an UNDER permission flag for this, but for now,
         * demand that creator of a child table own the parent.
         */
        if (!pg_class_ownercheck(RelationGetRelid(relation), GetUserId()))
            aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
                           RelationGetRelationName(relation));

        /*
         * Reject duplications in the list of parents.
         */
        if (list_member_oid(parentOids, RelationGetRelid(relation)))
            ereport(ERROR,
                    (errcode(ERRCODE_DUPLICATE_TABLE),
             errmsg("relation \"%s\" would be inherited from more than once",
                    parent->relname)));

        parentOids = lappend_oid(parentOids, RelationGetRelid(relation));

        if (relation->rd_rel->relhasoids)
            parentsWithOids++;

        tupleDesc = RelationGetDescr(relation);
        constr = tupleDesc->constr;

        /*
         * newattno[] will contain the child-table attribute numbers for the
         * attributes of this parent table.  (They are not the same for
         * parents after the first one, nor if we have dropped columns.)
         */
        newattno = (AttrNumber *)
            palloc0(tupleDesc->natts * sizeof(AttrNumber));

        for (parent_attno = 1; parent_attno <= tupleDesc->natts;
             parent_attno++)
        {
            Form_pg_attribute attribute = tupleDesc->attrs[parent_attno - 1];
            char       *attributeName = NameStr(attribute->attname);
            int         exist_attno;
            ColumnDef  *def;

            /*
             * Ignore dropped columns in the parent.
             */
            if (attribute->attisdropped)
                continue;       /* leave newattno entry as zero */

            /*
             * Does it conflict with some previously inherited column?
             */
            exist_attno = findAttrByName(attributeName, inhSchema);
            if (exist_attno > 0)
            {
                Oid         defTypeId;
                int32       deftypmod;
                Oid         defCollId;

                /*
                 * Yes, try to merge the two column definitions. They must
                 * have the same type, typmod, and collation.
                 */
                ereport(NOTICE,
                        (errmsg("merging multiple inherited definitions of column \"%s\"",
                                attributeName)));
                def = (ColumnDef *) list_nth(inhSchema, exist_attno - 1);
                typenameTypeIdAndMod(NULL, def->typeName, &defTypeId, &deftypmod);
                if (defTypeId != attribute->atttypid ||
                    deftypmod != attribute->atttypmod)
                    ereport(ERROR,
                            (errcode(ERRCODE_DATATYPE_MISMATCH),
                        errmsg("inherited column \"%s\" has a type conflict",
                               attributeName),
                             errdetail("%s versus %s",
                                       TypeNameToString(def->typeName),
                                       format_type_be(attribute->atttypid))));
                defCollId = GetColumnDefCollation(NULL, def, defTypeId);
                if (defCollId != attribute->attcollation)
                    ereport(ERROR,
                            (errcode(ERRCODE_COLLATION_MISMATCH),
                    errmsg("inherited column \"%s\" has a collation conflict",
                           attributeName),
                             errdetail("\"%s\" versus \"%s\"",
                                       get_collation_name(defCollId),
                              get_collation_name(attribute->attcollation))));

                /* Copy storage parameter */
                if (def->storage == 0)
                    def->storage = attribute->attstorage;
                else if (def->storage != attribute->attstorage)
                    ereport(ERROR,
                            (errcode(ERRCODE_DATATYPE_MISMATCH),
                             errmsg("inherited column \"%s\" has a storage parameter conflict",
                                    attributeName),
                             errdetail("%s versus %s",
                                       storage_name(def->storage),
                                       storage_name(attribute->attstorage))));

                def->inhcount++;
                /* Merge of NOT NULL constraints = OR 'em together */
                def->is_not_null |= attribute->attnotnull;
                /* Default and other constraints are handled below */
                newattno[parent_attno - 1] = exist_attno;
            }
            else
            {
                /*
                 * No, create a new inherited column
                 */
                def = makeNode(ColumnDef);
                def->colname = pstrdup(attributeName);
                def->typeName = makeTypeNameFromOid(attribute->atttypid,
                                                    attribute->atttypmod);
                def->inhcount = 1;
                def->is_local = false;
                def->is_not_null = attribute->attnotnull;
                def->is_from_type = false;
                def->storage = attribute->attstorage;
                def->raw_default = NULL;
                def->cooked_default = NULL;
                def->collClause = NULL;
                def->collOid = attribute->attcollation;
                def->constraints = NIL;
                inhSchema = lappend(inhSchema, def);
                newattno[parent_attno - 1] = ++child_attno;
            }

            /*
             * Copy default if any
             */
            if (attribute->atthasdef)
            {
                Node       *this_default = NULL;
                AttrDefault *attrdef;
                int         i;

                /* Find default in constraint structure */
                Assert(constr != NULL);
                attrdef = constr->defval;
                for (i = 0; i < constr->num_defval; i++)
                {
                    if (attrdef[i].adnum == parent_attno)
                    {
                        this_default = stringToNode(attrdef[i].adbin);
                        break;
                    }
                }
                Assert(this_default != NULL);

                /*
                 * If default expr could contain any vars, we'd need to fix
                 * 'em, but it can't; so default is ready to apply to child.
                 *
                 * If we already had a default from some prior parent, check
                 * to see if they are the same.  If so, no problem; if not,
                 * mark the column as having a bogus default. Below, we will
                 * complain if the bogus default isn't overridden by the child
                 * schema.
                 */
                Assert(def->raw_default == NULL);
                if (def->cooked_default == NULL)
                    def->cooked_default = this_default;
                else if (!equal(def->cooked_default, this_default))
                {
                    def->cooked_default = &bogus_marker;
                    have_bogus_defaults = true;
                }
            }
        }

        /*
         * Now copy the CHECK constraints of this parent, adjusting attnos
         * using the completed newattno[] map.  Identically named constraints
         * are merged if possible, else we throw error.
         */
        if (constr && constr->num_check > 0)
        {
            ConstrCheck *check = constr->check;
            int         i;

            for (i = 0; i < constr->num_check; i++)
            {
                char       *name = check[i].ccname;
                Node       *expr;
                bool        found_whole_row;

                /* ignore if the constraint is non-inheritable */
                if (check[i].ccnoinherit)
                    continue;

                /* Adjust Vars to match new table's column numbering */
                expr = map_variable_attnos(stringToNode(check[i].ccbin),
                                           1, 0,
                                           newattno, tupleDesc->natts,
                                           &found_whole_row);

                /*
                 * For the moment we have to reject whole-row variables.
                 * We could convert them, if we knew the new table's rowtype
                 * OID, but that hasn't been assigned yet.
                 */
                if (found_whole_row)
                    ereport(ERROR,
                            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                             errmsg("cannot convert whole-row table reference"),
                             errdetail("Constraint \"%s\" contains a whole-row reference to table \"%s\".",
                                       name,
                                       RelationGetRelationName(relation))));

                /* check for duplicate */
                if (!MergeCheckConstraint(constraints, name, expr))
                {
                    /* nope, this is a new one */
                    CookedConstraint *cooked;

                    cooked = (CookedConstraint *) palloc(sizeof(CookedConstraint));
                    cooked->contype = CONSTR_CHECK;
                    cooked->name = pstrdup(name);
                    cooked->attnum = 0; /* not used for constraints */
                    cooked->expr = expr;
                    cooked->skip_validation = false;
                    cooked->is_local = false;
                    cooked->inhcount = 1;
                    cooked->is_no_inherit = false;
                    constraints = lappend(constraints, cooked);
                }
            }
        }

        pfree(newattno);

        /*
         * Close the parent rel, but keep our AccessShareLock on it until xact
         * commit.  That will prevent someone else from deleting or ALTERing
         * the parent before the child is committed.
         */
        heap_close(relation, NoLock);
    }

    /*
     * If we had no inherited attributes, the result schema is just the
     * explicitly declared columns.  Otherwise, we need to merge the declared
     * columns into the inherited schema list.
     */
    if (inhSchema != NIL)
    {
        foreach(entry, schema)
        {
            ColumnDef  *newdef = lfirst(entry);
            char       *attributeName = newdef->colname;
            int         exist_attno;

            /*
             * Does it conflict with some previously inherited column?
             */
            exist_attno = findAttrByName(attributeName, inhSchema);
            if (exist_attno > 0)
            {
                ColumnDef  *def;
                Oid         defTypeId,
                            newTypeId;
                int32       deftypmod,
                            newtypmod;
                Oid         defcollid,
                            newcollid;

                /*
                 * Yes, try to merge the two column definitions. They must
                 * have the same type, typmod, and collation.
                 */
                ereport(NOTICE,
                   (errmsg("merging column \"%s\" with inherited definition",
                           attributeName)));
                def = (ColumnDef *) list_nth(inhSchema, exist_attno - 1);
                typenameTypeIdAndMod(NULL, def->typeName, &defTypeId, &deftypmod);
                typenameTypeIdAndMod(NULL, newdef->typeName, &newTypeId, &newtypmod);
                if (defTypeId != newTypeId || deftypmod != newtypmod)
                    ereport(ERROR,
                            (errcode(ERRCODE_DATATYPE_MISMATCH),
                             errmsg("column \"%s\" has a type conflict",
                                    attributeName),
                             errdetail("%s versus %s",
                                       TypeNameToString(def->typeName),
                                       TypeNameToString(newdef->typeName))));
                defcollid = GetColumnDefCollation(NULL, def, defTypeId);
                newcollid = GetColumnDefCollation(NULL, newdef, newTypeId);
                if (defcollid != newcollid)
                    ereport(ERROR,
                            (errcode(ERRCODE_COLLATION_MISMATCH),
                             errmsg("column \"%s\" has a collation conflict",
                                    attributeName),
                             errdetail("\"%s\" versus \"%s\"",
                                       get_collation_name(defcollid),
                                       get_collation_name(newcollid))));

                /* Copy storage parameter */
                if (def->storage == 0)
                    def->storage = newdef->storage;
                else if (newdef->storage != 0 && def->storage != newdef->storage)
                    ereport(ERROR,
                            (errcode(ERRCODE_DATATYPE_MISMATCH),
                     errmsg("column \"%s\" has a storage parameter conflict",
                            attributeName),
                             errdetail("%s versus %s",
                                       storage_name(def->storage),
                                       storage_name(newdef->storage))));

                /* Mark the column as locally defined */
                def->is_local = true;
                /* Merge of NOT NULL constraints = OR 'em together */
                def->is_not_null |= newdef->is_not_null;
                /* If new def has a default, override previous default */
                if (newdef->raw_default != NULL)
                {
                    def->raw_default = newdef->raw_default;
                    def->cooked_default = newdef->cooked_default;
                }
            }
            else
            {
                /*
                 * No, attach new column to result schema
                 */
                inhSchema = lappend(inhSchema, newdef);
            }
        }

        schema = inhSchema;

        /*
         * Check that we haven't exceeded the legal # of columns after merging
         * in inherited columns.
         */
        if (list_length(schema) > MaxHeapAttributeNumber)
            ereport(ERROR,
                    (errcode(ERRCODE_TOO_MANY_COLUMNS),
                     errmsg("tables can have at most %d columns",
                            MaxHeapAttributeNumber)));
    }

    /*
     * If we found any conflicting parent default values, check to make sure
     * they were overridden by the child.
     */
    if (have_bogus_defaults)
    {
        foreach(entry, schema)
        {
            ColumnDef  *def = lfirst(entry);

            if (def->cooked_default == &bogus_marker)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_COLUMN_DEFINITION),
                  errmsg("column \"%s\" inherits conflicting default values",
                         def->colname),
                         errhint("To resolve the conflict, specify a default explicitly.")));
        }
    }

    *supOids = parentOids;
    *supconstr = constraints;
    *supOidCount = parentsWithOids;
    return schema;
}


/*
 * MergeCheckConstraint
 *      Try to merge an inherited CHECK constraint with previous ones
 *
 * If we inherit identically-named constraints from multiple parents, we must
 * merge them, or throw an error if they don't have identical definitions.
 *
 * constraints is a list of CookedConstraint structs for previous constraints.
 *
 * Returns TRUE if merged (constraint is a duplicate), or FALSE if it's
 * got a so-far-unique name, or throws error if conflict.
 */
static bool
MergeCheckConstraint(List *constraints, char *name, Node *expr)
{
    ListCell   *lc;

    foreach(lc, constraints)
    {
        CookedConstraint *ccon = (CookedConstraint *) lfirst(lc);

        Assert(ccon->contype == CONSTR_CHECK);

        /* Non-matching names never conflict */
        if (strcmp(ccon->name, name) != 0)
            continue;

        if (equal(expr, ccon->expr))
        {
            /* OK to merge */
            ccon->inhcount++;
            return true;
        }

        ereport(ERROR,
                (errcode(ERRCODE_DUPLICATE_OBJECT),
                 errmsg("check constraint name \"%s\" appears multiple times but with different expressions",
                        name)));
    }

    return false;
}


/*
 * StoreCatalogInheritance
 *      Updates the system catalogs with proper inheritance information.
 *
 * supers is a list of the OIDs of the new relation's direct ancestors.
 */
static void
StoreCatalogInheritance(Oid relationId, List *supers)
{
    Relation    relation;
    int16       seqNumber;
    ListCell   *entry;

    /*
     * sanity checks
     */
    AssertArg(OidIsValid(relationId));

    if (supers == NIL)
        return;

    /*
     * Store INHERITS information in pg_inherits using direct ancestors only.
     * Also enter dependencies on the direct ancestors, and make sure they are
     * marked with relhassubclass = true.
     *
     * (Once upon a time, both direct and indirect ancestors were found here
     * and then entered into pg_ipl.  Since that catalog doesn't exist
     * anymore, there's no need to look for indirect ancestors.)
     */
    relation = heap_open(InheritsRelationId, RowExclusiveLock);

    seqNumber = 1;
    foreach(entry, supers)
    {
        Oid         parentOid = lfirst_oid(entry);

        StoreCatalogInheritance1(relationId, parentOid, seqNumber, relation);
        seqNumber++;
    }

    heap_close(relation, RowExclusiveLock);
}

/*
 * Make catalog entries showing relationId as being an inheritance child
 * of parentOid.  inhRelation is the already-opened pg_inherits catalog.
 */
static void
StoreCatalogInheritance1(Oid relationId, Oid parentOid,
                         int16 seqNumber, Relation inhRelation)
{
    TupleDesc   desc = RelationGetDescr(inhRelation);
    Datum       values[Natts_pg_inherits];
    bool        nulls[Natts_pg_inherits];
    ObjectAddress childobject,
                parentobject;
    HeapTuple   tuple;

    /*
     * Make the pg_inherits entry
     */
    values[Anum_pg_inherits_inhrelid - 1] = ObjectIdGetDatum(relationId);
    values[Anum_pg_inherits_inhparent - 1] = ObjectIdGetDatum(parentOid);
    values[Anum_pg_inherits_inhseqno - 1] = Int16GetDatum(seqNumber);

    memset(nulls, 0, sizeof(nulls));

    tuple = heap_form_tuple(desc, values, nulls);

    simple_heap_insert(inhRelation, tuple);

    CatalogUpdateIndexes(inhRelation, tuple);

    heap_freetuple(tuple);

    /*
     * Store a dependency too
     */
    parentobject.classId = RelationRelationId;
    parentobject.objectId = parentOid;
    parentobject.objectSubId = 0;
    childobject.classId = RelationRelationId;
    childobject.objectId = relationId;
    childobject.objectSubId = 0;

    recordDependencyOn(&childobject, &parentobject, DEPENDENCY_NORMAL);

    /*
     * Post creation hook of this inheritance. Since object_access_hook
     * doesn't take multiple object identifiers, we relay oid of parent
     * relation using auxiliary_id argument.
     */
    InvokeObjectPostAlterHookArg(InheritsRelationId,
                                 relationId, 0,
                                 parentOid, false);

    /*
     * Mark the parent as having subclasses.
     */
    SetRelationHasSubclass(parentOid, true);
}

/*
 * Look for an existing schema entry with the given name.
 *
 * Returns the index (starting with 1) if attribute already exists in schema,
 * 0 if it doesn't.
 */
static int
findAttrByName(const char *attributeName, List *schema)
{
    ListCell   *s;
    int         i = 1;

    foreach(s, schema)
    {
        ColumnDef  *def = lfirst(s);

        if (strcmp(attributeName, def->colname) == 0)
            return i;

        i++;
    }
    return 0;
}


/*
 * SetRelationHasSubclass
 *      Set the value of the relation's relhassubclass field in pg_class.
 *
 * NOTE: caller must be holding an appropriate lock on the relation.
 * ShareUpdateExclusiveLock is sufficient.
 *
 * NOTE: an important side-effect of this operation is that an SI invalidation
 * message is sent out to all backends --- including me --- causing plans
 * referencing the relation to be rebuilt with the new list of children.
 * This must happen even if we find that no change is needed in the pg_class
 * row.
 */
void
SetRelationHasSubclass(Oid relationId, bool relhassubclass)
{
    Relation    relationRelation;
    HeapTuple   tuple;
    Form_pg_class classtuple;

    /*
     * Fetch a modifiable copy of the tuple, modify it, update pg_class.
     */
    relationRelation = heap_open(RelationRelationId, RowExclusiveLock);
    tuple = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(relationId));
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for relation %u", relationId);
    classtuple = (Form_pg_class) GETSTRUCT(tuple);

    if (classtuple->relhassubclass != relhassubclass)
    {
        classtuple->relhassubclass = relhassubclass;
        simple_heap_update(relationRelation, &tuple->t_self, tuple);

        /* keep the catalog indexes up to date */
        CatalogUpdateIndexes(relationRelation, tuple);
    }
    else
    {
        /* no need to change tuple, but force relcache rebuild anyway */
        CacheInvalidateRelcacheByTuple(tuple);
    }

    heap_freetuple(tuple);
    heap_close(relationRelation, RowExclusiveLock);
}

/*
 *      renameatt_check         - basic sanity checks before attribute rename
 */
static void
renameatt_check(Oid myrelid, Form_pg_class classform, bool recursing)
{
    char        relkind = classform->relkind;

    if (classform->reloftype && !recursing)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("cannot rename column of typed table")));

    /*
     * Renaming the columns of sequences or toast tables doesn't actually
     * break anything from the system's point of view, since internal
     * references are by attnum.  But it doesn't seem right to allow users to
     * change names that are hardcoded into the system, hence the following
     * restriction.
     */
    if (relkind != RELKIND_RELATION &&
        relkind != RELKIND_VIEW &&
        relkind != RELKIND_MATVIEW &&
        relkind != RELKIND_COMPOSITE_TYPE &&
        relkind != RELKIND_INDEX &&
        relkind != RELKIND_FOREIGN_TABLE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not a table, view, materialized view, composite type, index, or foreign table",
                        NameStr(classform->relname))));

    /*
     * permissions checking.  only the owner of a class can change its schema.
     */
    if (!pg_class_ownercheck(myrelid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
                       NameStr(classform->relname));
    if (!allowSystemTableMods && IsSystemClass(classform))
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied: \"%s\" is a system catalog",
                        NameStr(classform->relname))));
}

/*
 *      renameatt_internal      - workhorse for renameatt
 */
static void
renameatt_internal(Oid myrelid,
                   const char *oldattname,
                   const char *newattname,
                   bool recurse,
                   bool recursing,
                   int expected_parents,
                   DropBehavior behavior)
{
    Relation    targetrelation;
    Relation    attrelation;
    HeapTuple   atttup;
    Form_pg_attribute   attform;
    int         attnum;

    /*
     * Grab an exclusive lock on the target table, which we will NOT release
     * until end of transaction.
     */
    targetrelation = relation_open(myrelid, AccessExclusiveLock);
    renameatt_check(myrelid, RelationGetForm(targetrelation), recursing);

    /*
     * if the 'recurse' flag is set then we are supposed to rename this
     * attribute in all classes that inherit from 'relname' (as well as in
     * 'relname').
     *
     * any permissions or problems with duplicate attributes will cause the
     * whole transaction to abort, which is what we want -- all or nothing.
     */
    if (recurse)
    {
        List       *child_oids,
                   *child_numparents;
        ListCell   *lo,
                   *li;

        /*
         * we need the number of parents for each child so that the recursive
         * calls to renameatt() can determine whether there are any parents
         * outside the inheritance hierarchy being processed.
         */
        child_oids = find_all_inheritors(myrelid, AccessExclusiveLock,
                                         &child_numparents);

        /*
         * find_all_inheritors does the recursive search of the inheritance
         * hierarchy, so all we have to do is process all of the relids in the
         * list that it returns.
         */
        forboth(lo, child_oids, li, child_numparents)
        {
            Oid         childrelid = lfirst_oid(lo);
            int         numparents = lfirst_int(li);

            if (childrelid == myrelid)
                continue;
            /* note we need not recurse again */
            renameatt_internal(childrelid, oldattname, newattname, false, true, numparents, behavior);
        }
    }
    else
    {
        /*
         * If we are told not to recurse, there had better not be any child
         * tables; else the rename would put them out of step.
         *
         * expected_parents will only be 0 if we are not already recursing.
         */
        if (expected_parents == 0 &&
            find_inheritance_children(myrelid, NoLock) != NIL)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                     errmsg("inherited column \"%s\" must be renamed in child tables too",
                            oldattname)));
    }

    /* rename attributes in typed tables of composite type */
    if (targetrelation->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
    {
        List       *child_oids;
        ListCell   *lo;

        child_oids = find_typed_table_dependencies(targetrelation->rd_rel->reltype,
                                     RelationGetRelationName(targetrelation),
                                                   behavior);

        foreach(lo, child_oids)
            renameatt_internal(lfirst_oid(lo), oldattname, newattname, true, true, 0, behavior);
    }

    attrelation = heap_open(AttributeRelationId, RowExclusiveLock);

    atttup = SearchSysCacheCopyAttName(myrelid, oldattname);
    if (!HeapTupleIsValid(atttup))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_COLUMN),
                 errmsg("column \"%s\" does not exist",
                        oldattname)));
    attform = (Form_pg_attribute) GETSTRUCT(atttup);

    attnum = attform->attnum;
    if (attnum <= 0)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot rename system column \"%s\"",
                        oldattname)));

    /*
     * if the attribute is inherited, forbid the renaming.  if this is a
     * top-level call to renameatt(), then expected_parents will be 0, so the
     * effect of this code will be to prohibit the renaming if the attribute
     * is inherited at all.  if this is a recursive call to renameatt(),
     * expected_parents will be the number of parents the current relation has
     * within the inheritance hierarchy being processed, so we'll prohibit the
     * renaming only if there are additional parents from elsewhere.
     */
    if (attform->attinhcount > expected_parents)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                 errmsg("cannot rename inherited column \"%s\"",
                        oldattname)));

    /* new name should not already exist */
    check_for_column_name_collision(targetrelation, newattname);

    /* apply the update */
    namestrcpy(&(attform->attname), newattname);

    simple_heap_update(attrelation, &atttup->t_self, atttup);

    /* keep system catalog indexes current */
    CatalogUpdateIndexes(attrelation, atttup);

    InvokeObjectPostAlterHook(RelationRelationId, myrelid, attnum);

    heap_freetuple(atttup);

    heap_close(attrelation, RowExclusiveLock);

    relation_close(targetrelation, NoLock);     /* close rel but keep lock */
}

/*
 * Perform permissions and integrity checks before acquiring a relation lock.
 */
static void
RangeVarCallbackForRenameAttribute(const RangeVar *rv, Oid relid, Oid oldrelid,
                                   void *arg)
{
    HeapTuple   tuple;
    Form_pg_class form;

    tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
    if (!HeapTupleIsValid(tuple))
        return;                 /* concurrently dropped */
    form = (Form_pg_class) GETSTRUCT(tuple);
    renameatt_check(relid, form, false);
    ReleaseSysCache(tuple);
}

/*
 *      renameatt       - changes the name of a attribute in a relation
 */
Oid
renameatt(RenameStmt *stmt)
{
    Oid         relid;

    /* lock level taken here should match renameatt_internal */
    relid = RangeVarGetRelidExtended(stmt->relation, AccessExclusiveLock,
                                     stmt->missing_ok, false,
                                     RangeVarCallbackForRenameAttribute,
                                     NULL);

    if (!OidIsValid(relid))
    {
        ereport(NOTICE,
                (errmsg("relation \"%s\" does not exist, skipping",
                        stmt->relation->relname)));
        return InvalidOid;
    }

    renameatt_internal(relid,
                       stmt->subname,   /* old att name */
                       stmt->newname,   /* new att name */
                       interpretInhOption(stmt->relation->inhOpt),      /* recursive? */
                       false,   /* recursing? */
                       0,       /* expected inhcount */
                       stmt->behavior);

    /* This is an ALTER TABLE command so it's about the relid */
    return relid;
}


/*
 * same logic as renameatt_internal
 */
static Oid
rename_constraint_internal(Oid myrelid,
                           Oid mytypid,
                           const char *oldconname,
                           const char *newconname,
                           bool recurse,
                           bool recursing,
                           int expected_parents)
{
    Relation    targetrelation = NULL;
    Oid         constraintOid;
    HeapTuple   tuple;
    Form_pg_constraint con;

    AssertArg(!myrelid || !mytypid);

    if (mytypid)
    {
        constraintOid = get_domain_constraint_oid(mytypid, oldconname, false);
    }
    else
    {
        targetrelation = relation_open(myrelid, AccessExclusiveLock);

        /*
         * don't tell it whether we're recursing; we allow changing typed
         * tables here
         */
        renameatt_check(myrelid, RelationGetForm(targetrelation), false);

        constraintOid = get_relation_constraint_oid(myrelid, oldconname, false);
    }

    tuple = SearchSysCache1(CONSTROID, ObjectIdGetDatum(constraintOid));
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for constraint %u",
             constraintOid);
    con = (Form_pg_constraint) GETSTRUCT(tuple);

    if (myrelid && con->contype == CONSTRAINT_CHECK && !con->connoinherit)
    {
        if (recurse)
        {
            List       *child_oids,
                       *child_numparents;
            ListCell   *lo,
                       *li;

            child_oids = find_all_inheritors(myrelid, AccessExclusiveLock,
                                             &child_numparents);

            forboth(lo, child_oids, li, child_numparents)
            {
                Oid         childrelid = lfirst_oid(lo);
                int         numparents = lfirst_int(li);

                if (childrelid == myrelid)
                    continue;

                rename_constraint_internal(childrelid, InvalidOid, oldconname, newconname, false, true, numparents);
            }
        }
        else
        {
            if (expected_parents == 0 &&
                find_inheritance_children(myrelid, NoLock) != NIL)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                         errmsg("inherited constraint \"%s\" must be renamed in child tables too",
                                oldconname)));
        }

        if (con->coninhcount > expected_parents)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                     errmsg("cannot rename inherited constraint \"%s\"",
                            oldconname)));
    }

    if (con->conindid
        && (con->contype == CONSTRAINT_PRIMARY
            || con->contype == CONSTRAINT_UNIQUE
            || con->contype == CONSTRAINT_EXCLUSION))
        /* rename the index; this renames the constraint as well */
        RenameRelationInternal(con->conindid, newconname, false);
    else
        RenameConstraintById(constraintOid, newconname);

    ReleaseSysCache(tuple);

    if (targetrelation)
        relation_close(targetrelation, NoLock); /* close rel but keep lock */

    return constraintOid;
}

Oid
RenameConstraint(RenameStmt *stmt)
{
    Oid         relid = InvalidOid;
    Oid         typid = InvalidOid;

    if (stmt->relationType == OBJECT_DOMAIN)
    {
        Relation    rel;
        HeapTuple   tup;

        typid = typenameTypeId(NULL, makeTypeNameFromNameList(stmt->object));
        rel = heap_open(TypeRelationId, RowExclusiveLock);
        tup = SearchSysCache1(TYPEOID, ObjectIdGetDatum(typid));
        if (!HeapTupleIsValid(tup))
            elog(ERROR, "cache lookup failed for type %u", typid);
        checkDomainOwner(tup);
        ReleaseSysCache(tup);
        heap_close(rel, NoLock);
    }
    else
    {
        /* lock level taken here should match rename_constraint_internal */
        relid = RangeVarGetRelidExtended(stmt->relation, AccessExclusiveLock,
                                         false, false,
                                         RangeVarCallbackForRenameAttribute,
                                         NULL);
    }

    return
        rename_constraint_internal(relid, typid,
                                   stmt->subname,
                                   stmt->newname,
                                   stmt->relation ? interpretInhOption(stmt->relation->inhOpt) : false, /* recursive? */
                                   false,   /* recursing? */
                                   0 /* expected inhcount */ );

}

/*
 * Execute ALTER TABLE/INDEX/SEQUENCE/VIEW/FOREIGN TABLE RENAME
 */
Oid
RenameRelation(RenameStmt *stmt)
{
    Oid         relid;

    /*
     * Grab an exclusive lock on the target table, index, sequence or view,
     * which we will NOT release until end of transaction.
     *
     * Lock level used here should match RenameRelationInternal, to avoid lock
     * escalation.
     */
    relid = RangeVarGetRelidExtended(stmt->relation, AccessExclusiveLock,
                                     stmt->missing_ok, false,
                                     RangeVarCallbackForAlterRelation,
                                     (void *) stmt);

    if (!OidIsValid(relid))
    {
        ereport(NOTICE,
                (errmsg("relation \"%s\" does not exist, skipping",
                        stmt->relation->relname)));
        return InvalidOid;
    }

    /* Do the work */
    RenameRelationInternal(relid, stmt->newname, false);

    return relid;
}

/*
 *      RenameRelationInternal - change the name of a relation
 *
 *      XXX - When renaming sequences, we don't bother to modify the
 *            sequence name that is stored within the sequence itself
 *            (this would cause problems with MVCC). In the future,
 *            the sequence name should probably be removed from the
 *            sequence, AFAIK there's no need for it to be there.
 */
void
RenameRelationInternal(Oid myrelid, const char *newrelname, bool is_internal)
{
    Relation    targetrelation;
    Relation    relrelation;    /* for RELATION relation */
    HeapTuple   reltup;
    Form_pg_class relform;
    Oid         namespaceId;

    /*
     * Grab an exclusive lock on the target table, index, sequence or view,
     * which we will NOT release until end of transaction.
     */
    targetrelation = relation_open(myrelid, AccessExclusiveLock);
    namespaceId = RelationGetNamespace(targetrelation);

    /*
     * Find relation's pg_class tuple, and make sure newrelname isn't in use.
     */
    relrelation = heap_open(RelationRelationId, RowExclusiveLock);

    reltup = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(myrelid));
    if (!HeapTupleIsValid(reltup))      /* shouldn't happen */
        elog(ERROR, "cache lookup failed for relation %u", myrelid);
    relform = (Form_pg_class) GETSTRUCT(reltup);

    if (get_relname_relid(newrelname, namespaceId) != InvalidOid)
        ereport(ERROR,
                (errcode(ERRCODE_DUPLICATE_TABLE),
                 errmsg("relation \"%s\" already exists",
                        newrelname)));

    /*
     * Update pg_class tuple with new relname.  (Scribbling on reltup is OK
     * because it's a copy...)
     */
    namestrcpy(&(relform->relname), newrelname);

    simple_heap_update(relrelation, &reltup->t_self, reltup);

    /* keep the system catalog indexes current */
    CatalogUpdateIndexes(relrelation, reltup);

    InvokeObjectPostAlterHookArg(RelationRelationId, myrelid, 0,
                                 InvalidOid, is_internal);

    heap_freetuple(reltup);
    heap_close(relrelation, RowExclusiveLock);

    /*
     * Also rename the associated type, if any.
     */
    if (OidIsValid(targetrelation->rd_rel->reltype))
        RenameTypeInternal(targetrelation->rd_rel->reltype,
                           newrelname, namespaceId);

    /*
     * Also rename the associated constraint, if any.
     */
    if (targetrelation->rd_rel->relkind == RELKIND_INDEX)
    {
        Oid         constraintId = get_index_constraint(myrelid);

        if (OidIsValid(constraintId))
            RenameConstraintById(constraintId, newrelname);
    }

    /*
     * Close rel, but keep exclusive lock!
     */
    relation_close(targetrelation, NoLock);
}

/*
 * Disallow ALTER TABLE (and similar commands) when the current backend has
 * any open reference to the target table besides the one just acquired by
 * the calling command; this implies there's an open cursor or active plan.
 * We need this check because our lock doesn't protect us against stomping
 * on our own foot, only other people's feet!
 *
 * For ALTER TABLE, the only case known to cause serious trouble is ALTER
 * COLUMN TYPE, and some changes are obviously pretty benign, so this could
 * possibly be relaxed to only error out for certain types of alterations.
 * But the use-case for allowing any of these things is not obvious, so we
 * won't work hard at it for now.
 *
 * We also reject these commands if there are any pending AFTER trigger events
 * for the rel.  This is certainly necessary for the rewriting variants of
 * ALTER TABLE, because they don't preserve tuple TIDs and so the pending
 * events would try to fetch the wrong tuples.  It might be overly cautious
 * in other cases, but again it seems better to err on the side of paranoia.
 *
 * REINDEX calls this with "rel" referencing the index to be rebuilt; here
 * we are worried about active indexscans on the index.  The trigger-event
 * check can be skipped, since we are doing no damage to the parent table.
 *
 * The statement name (eg, "ALTER TABLE") is passed for use in error messages.
 */
void
CheckTableNotInUse(Relation rel, const char *stmt)
{
    int         expected_refcnt;

    expected_refcnt = rel->rd_isnailed ? 2 : 1;
    if (rel->rd_refcnt != expected_refcnt)
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_IN_USE),
        /* translator: first %s is a SQL command, eg ALTER TABLE */
                 errmsg("cannot %s \"%s\" because "
                        "it is being used by active queries in this session",
                        stmt, RelationGetRelationName(rel))));

    if (rel->rd_rel->relkind != RELKIND_INDEX &&
        AfterTriggerPendingOnRel(RelationGetRelid(rel)))
        ereport(ERROR,
                (errcode(ERRCODE_OBJECT_IN_USE),
        /* translator: first %s is a SQL command, eg ALTER TABLE */
                 errmsg("cannot %s \"%s\" because "
                        "it has pending trigger events",
                        stmt, RelationGetRelationName(rel))));
}

/*
 * AlterTableLookupRelation
 *      Look up, and lock, the OID for the relation named by an alter table
 *      statement.
 */
Oid
AlterTableLookupRelation(AlterTableStmt *stmt, LOCKMODE lockmode)
{
    return RangeVarGetRelidExtended(stmt->relation, lockmode, stmt->missing_ok, false,
                                    RangeVarCallbackForAlterRelation,
                                    (void *) stmt);
}

/*
 * AlterTable
 *      Execute ALTER TABLE, which can be a list of subcommands
 *
 * ALTER TABLE is performed in three phases:
 *      1. Examine subcommands and perform pre-transformation checking.
 *      2. Update system catalogs.
 *      3. Scan table(s) to check new constraints, and optionally recopy
 *         the data into new table(s).
 * Phase 3 is not performed unless one or more of the subcommands requires
 * it.  The intention of this design is to allow multiple independent
 * updates of the table schema to be performed with only one pass over the
 * data.
 *
 * ATPrepCmd performs phase 1.  A "work queue" entry is created for
 * each table to be affected (there may be multiple affected tables if the
 * commands traverse a table inheritance hierarchy).  Also we do preliminary
 * validation of the subcommands, including parse transformation of those
 * expressions that need to be evaluated with respect to the old table
 * schema.
 *
 * ATRewriteCatalogs performs phase 2 for each affected table.  (Note that
 * phases 2 and 3 normally do no explicit recursion, since phase 1 already
 * did it --- although some subcommands have to recurse in phase 2 instead.)
 * Certain subcommands need to be performed before others to avoid
 * unnecessary conflicts; for example, DROP COLUMN should come before
 * ADD COLUMN.  Therefore phase 1 divides the subcommands into multiple
 * lists, one for each logical "pass" of phase 2.
 *
 * ATRewriteTables performs phase 3 for those tables that need it.
 *
 * Thanks to the magic of MVCC, an error anywhere along the way rolls back
 * the whole operation; we don't have to do anything special to clean up.
 *
 * The caller must lock the relation, with an appropriate lock level
 * for the subcommands requested. Any subcommand that needs to rewrite
 * tuples in the table forces the whole command to be executed with
 * AccessExclusiveLock (actually, that is currently required always, but
 * we hope to relax it at some point).  We pass the lock level down
 * so that we can apply it recursively to inherited tables. Note that the
 * lock level we want as we recurse might well be higher than required for
 * that specific subcommand. So we pass down the overall lock requirement,
 * rather than reassess it at lower levels.
 */
void
AlterTable(Oid relid, LOCKMODE lockmode, AlterTableStmt *stmt)
{
    Relation    rel;

    /* Caller is required to provide an adequate lock. */
    rel = relation_open(relid, NoLock);

    CheckTableNotInUse(rel, "ALTER TABLE");

    ATController(rel, stmt->cmds, interpretInhOption(stmt->relation->inhOpt),
                 lockmode);
}

/*
 * AlterTableInternal
 *
 * ALTER TABLE with target specified by OID
 *
 * We do not reject if the relation is already open, because it's quite
 * likely that one or more layers of caller have it open.  That means it
 * is unsafe to use this entry point for alterations that could break
 * existing query plans.  On the assumption it's not used for such, we
 * don't have to reject pending AFTER triggers, either.
 */
void
AlterTableInternal(Oid relid, List *cmds, bool recurse)
{
    Relation    rel;
    LOCKMODE    lockmode = AlterTableGetLockLevel(cmds);

    rel = relation_open(relid, lockmode);

    ATController(rel, cmds, recurse, lockmode);
}

/*
 * AlterTableGetLockLevel
 *
 * Sets the overall lock level required for the supplied list of subcommands.
 * Policy for doing this set according to needs of AlterTable(), see
 * comments there for overall explanation.
 *
 * Function is called before and after parsing, so it must give same
 * answer each time it is called. Some subcommands are transformed
 * into other subcommand types, so the transform must never be made to a
 * lower lock level than previously assigned. All transforms are noted below.
 *
 * Since this is called before we lock the table we cannot use table metadata
 * to influence the type of lock we acquire.
 *
 * There should be no lockmodes hardcoded into the subcommand functions. All
 * lockmode decisions for ALTER TABLE are made here only. The one exception is
 * ALTER TABLE RENAME which is treated as a different statement type T_RenameStmt
 * and does not travel through this section of code and cannot be combined with
 * any of the subcommands given here.
 */
LOCKMODE
AlterTableGetLockLevel(List *cmds)
{
    /*
     * Late in 9.1 dev cycle a number of issues were uncovered with access to
     * catalog relations, leading to the decision to re-enforce all DDL at
     * AccessExclusiveLock level by default.
     *
     * The issues are that there is a pervasive assumption in the code that
     * the catalogs will not be read unless an AccessExclusiveLock is held. If
     * that rule is relaxed, we must protect against a number of potential
     * effects - infrequent, but proven possible with test cases where
     * multiple DDL operations occur in a stream against frequently accessed
     * tables.
     *
     * 1. Catalog tables are read using SnapshotNow, which has a race bug that
     * allows a scan to return no valid rows even when one is present in the
     * case of a commit of a concurrent update of the catalog table.
     * SnapshotNow also ignores transactions in progress, so takes the latest
     * committed version without waiting for the latest changes.
     *
     * 2. Relcache needs to be internally consistent, so unless we lock the
     * definition during reads we have no way to guarantee that.
     *
     * 3. Catcache access isn't coordinated at all so refreshes can occur at
     * any time.
     */
#ifdef REDUCED_ALTER_TABLE_LOCK_LEVELS
    ListCell   *lcmd;
    LOCKMODE    lockmode = ShareUpdateExclusiveLock;

    foreach(lcmd, cmds)
    {
        AlterTableCmd *cmd = (AlterTableCmd *) lfirst(lcmd);
        LOCKMODE    cmd_lockmode = AccessExclusiveLock; /* default for compiler */

        switch (cmd->subtype)
        {
                /*
                 * Need AccessExclusiveLock for these subcommands because they
                 * affect or potentially affect both read and write
                 * operations.
                 *
                 * New subcommand types should be added here by default.
                 */
            case AT_AddColumn:  /* may rewrite heap, in some cases and visible
                                 * to SELECT */
            case AT_DropColumn: /* change visible to SELECT */
            case AT_AddColumnToView:    /* CREATE VIEW */
            case AT_AlterColumnType:    /* must rewrite heap */
            case AT_DropConstraint:     /* as DROP INDEX */
            case AT_AddOids:    /* must rewrite heap */
            case AT_DropOids:   /* calls AT_DropColumn */
            case AT_EnableAlwaysRule:   /* may change SELECT rules */
            case AT_EnableReplicaRule:  /* may change SELECT rules */
            case AT_EnableRule: /* may change SELECT rules */
            case AT_DisableRule:        /* may change SELECT rules */
            case AT_ChangeOwner:        /* change visible to SELECT */
            case AT_SetTableSpace:      /* must rewrite heap */
            case AT_DropNotNull:        /* may change some SQL plans */
            case AT_SetNotNull:
            case AT_GenericOptions:
            case AT_AlterColumnGenericOptions:
                cmd_lockmode = AccessExclusiveLock;
                break;

                /*
                 * These subcommands affect write operations only.
                 */
            case AT_ColumnDefault:
            case AT_ProcessedConstraint:        /* becomes AT_AddConstraint */
            case AT_AddConstraintRecurse:       /* becomes AT_AddConstraint */
            case AT_ReAddConstraint:            /* becomes AT_AddConstraint */
            case AT_EnableTrig:
            case AT_EnableAlwaysTrig:
            case AT_EnableReplicaTrig:
            case AT_EnableTrigAll:
            case AT_EnableTrigUser:
            case AT_DisableTrig:
            case AT_DisableTrigAll:
            case AT_DisableTrigUser:
            case AT_AddIndex:   /* from ADD CONSTRAINT */
            case AT_AddIndexConstraint:
                cmd_lockmode = ShareRowExclusiveLock;
                break;

            case AT_AddConstraint:
                if (IsA(cmd->def, Constraint))
                {
                    Constraint *con = (Constraint *) cmd->def;

                    switch (con->contype)
                    {
                        case CONSTR_EXCLUSION:
                        case CONSTR_PRIMARY:
                        case CONSTR_UNIQUE:

                            /*
                             * Cases essentially the same as CREATE INDEX. We
                             * could reduce the lock strength to ShareLock if
                             * we can work out how to allow concurrent catalog
                             * updates.
                             */
                            cmd_lockmode = ShareRowExclusiveLock;
                            break;
                        case CONSTR_FOREIGN:

                            /*
                             * We add triggers to both tables when we add a
                             * Foreign Key, so the lock level must be at least
                             * as strong as CREATE TRIGGER.
                             */
                            cmd_lockmode = ShareRowExclusiveLock;
                            break;

                        default:
                            cmd_lockmode = ShareRowExclusiveLock;
                    }
                }
                break;

                /*
                 * These subcommands affect inheritance behaviour. Queries
                 * started before us will continue to see the old inheritance
                 * behaviour, while queries started after we commit will see
                 * new behaviour. No need to prevent reads or writes to the
                 * subtable while we hook it up though.
                 */
            case AT_AddInherit:
            case AT_DropInherit:
                cmd_lockmode = ShareUpdateExclusiveLock;
                break;

                /*
                 * These subcommands affect implicit row type conversion. They
                 * have affects similar to CREATE/DROP CAST on queries.  We
                 * don't provide for invalidating parse trees as a result of
                 * such changes.  Do avoid concurrent pg_class updates,
                 * though.
                 */
            case AT_AddOf:
            case AT_DropOf:
                cmd_lockmode = ShareUpdateExclusiveLock;

                /*
                 * These subcommands affect general strategies for performance
                 * and maintenance, though don't change the semantic results
                 * from normal data reads and writes. Delaying an ALTER TABLE
                 * behind currently active writes only delays the point where
                 * the new strategy begins to take effect, so there is no
                 * benefit in waiting. In this case the minimum restriction
                 * applies: we don't currently allow concurrent catalog
                 * updates.
                 */
            case AT_SetStatistics:
            case AT_ClusterOn:
            case AT_DropCluster:
            case AT_SetRelOptions:
            case AT_ResetRelOptions:
            case AT_ReplaceRelOptions:
            case AT_SetOptions:
            case AT_ResetOptions:
            case AT_SetStorage:
            case AT_ValidateConstraint:
                cmd_lockmode = ShareUpdateExclusiveLock;
                break;

            default:            /* oops */
                elog(ERROR, "unrecognized alter table type: %d",
                     (int) cmd->subtype);
                break;
        }

        /*
         * Take the greatest lockmode from any subcommand
         */
        if (cmd_lockmode > lockmode)
            lockmode = cmd_lockmode;
    }
#else
    LOCKMODE    lockmode = AccessExclusiveLock;
#endif

    return lockmode;
}

static void
ATController(Relation rel, List *cmds, bool recurse, LOCKMODE lockmode)
{
    List       *wqueue = NIL;
    ListCell   *lcmd;

    /* Phase 1: preliminary examination of commands, create work queue */
    foreach(lcmd, cmds)
    {
        AlterTableCmd *cmd = (AlterTableCmd *) lfirst(lcmd);

        ATPrepCmd(&wqueue, rel, cmd, recurse, false, lockmode);
    }

    /* Close the relation, but keep lock until commit */
    relation_close(rel, NoLock);

    /* Phase 2: update system catalogs */
    ATRewriteCatalogs(&wqueue, lockmode);

    /* Phase 3: scan/rewrite tables as needed */
    ATRewriteTables(&wqueue, lockmode);
}

/*
 * ATPrepCmd
 *
 * Traffic cop for ALTER TABLE Phase 1 operations, including simple
 * recursion and permission checks.
 *
 * Caller must have acquired appropriate lock type on relation already.
 * This lock should be held until commit.
 */
static void
ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
          bool recurse, bool recursing, LOCKMODE lockmode)
{
    AlteredTableInfo *tab;
    int         pass;

    /* Find or create work queue entry for this table */
    tab = ATGetQueueEntry(wqueue, rel);

    /*
     * Copy the original subcommand for each table.  This avoids conflicts
     * when different child tables need to make different parse
     * transformations (for example, the same column may have different column
     * numbers in different children).
     */
    cmd = copyObject(cmd);

    /*
     * Do permissions checking, recursion to child tables if needed, and any
     * additional phase-1 processing needed.
     */
    switch (cmd->subtype)
    {
        case AT_AddColumn:      /* ADD COLUMN */
            ATSimplePermissions(rel,
                         ATT_TABLE | ATT_COMPOSITE_TYPE | ATT_FOREIGN_TABLE);
            ATPrepAddColumn(wqueue, rel, recurse, recursing, cmd, lockmode);
            /* Recursion occurs during execution phase */
            pass = AT_PASS_ADD_COL;
            break;
        case AT_AddColumnToView:        /* add column via CREATE OR REPLACE
                                         * VIEW */
            ATSimplePermissions(rel, ATT_VIEW);
            ATPrepAddColumn(wqueue, rel, recurse, recursing, cmd, lockmode);
            /* Recursion occurs during execution phase */
            pass = AT_PASS_ADD_COL;
            break;
        case AT_ColumnDefault:  /* ALTER COLUMN DEFAULT */

            /*
             * We allow defaults on views so that INSERT into a view can have
             * default-ish behavior.  This works because the rewriter
             * substitutes default values into INSERTs before it expands
             * rules.
             */
            ATSimplePermissions(rel, ATT_TABLE | ATT_VIEW | ATT_FOREIGN_TABLE);
            ATSimpleRecursion(wqueue, rel, cmd, recurse, lockmode);
            /* No command-specific prep needed */
            pass = cmd->def ? AT_PASS_ADD_CONSTR : AT_PASS_DROP;
            break;
        case AT_DropNotNull:    /* ALTER COLUMN DROP NOT NULL */
            ATSimplePermissions(rel, ATT_TABLE | ATT_FOREIGN_TABLE);
            ATSimpleRecursion(wqueue, rel, cmd, recurse, lockmode);
            /* No command-specific prep needed */
            pass = AT_PASS_DROP;
            break;
        case AT_SetNotNull:     /* ALTER COLUMN SET NOT NULL */
            ATSimplePermissions(rel, ATT_TABLE | ATT_FOREIGN_TABLE);
            ATSimpleRecursion(wqueue, rel, cmd, recurse, lockmode);
            /* No command-specific prep needed */
            pass = AT_PASS_ADD_CONSTR;
            break;
        case AT_SetStatistics:  /* ALTER COLUMN SET STATISTICS */
            ATSimpleRecursion(wqueue, rel, cmd, recurse, lockmode);
            /* Performs own permission checks */
            ATPrepSetStatistics(rel, cmd->name, cmd->def, lockmode);
            pass = AT_PASS_MISC;
            break;
        case AT_SetOptions:     /* ALTER COLUMN SET ( options ) */
        case AT_ResetOptions:   /* ALTER COLUMN RESET ( options ) */
            ATSimplePermissions(rel, ATT_TABLE | ATT_MATVIEW | ATT_INDEX | ATT_FOREIGN_TABLE);
            /* This command never recurses */
            pass = AT_PASS_MISC;
            break;
        case AT_SetStorage:     /* ALTER COLUMN SET STORAGE */
            ATSimplePermissions(rel, ATT_TABLE | ATT_MATVIEW);
            ATSimpleRecursion(wqueue, rel, cmd, recurse, lockmode);
            /* No command-specific prep needed */
            pass = AT_PASS_MISC;
            break;
        case AT_DropColumn:     /* DROP COLUMN */
            ATSimplePermissions(rel,
                         ATT_TABLE | ATT_COMPOSITE_TYPE | ATT_FOREIGN_TABLE);
            ATPrepDropColumn(wqueue, rel, recurse, recursing, cmd, lockmode);
            /* Recursion occurs during execution phase */
            pass = AT_PASS_DROP;
            break;
        case AT_AddIndex:       /* ADD INDEX */
            ATSimplePermissions(rel, ATT_TABLE | ATT_MATVIEW);
            /* This command never recurses */
            /* No command-specific prep needed */
            pass = AT_PASS_ADD_INDEX;
            break;
        case AT_AddConstraint:  /* ADD CONSTRAINT */
            ATSimplePermissions(rel, ATT_TABLE);
            /* Recursion occurs during execution phase */
            /* No command-specific prep needed except saving recurse flag */
            if (recurse)
                cmd->subtype = AT_AddConstraintRecurse;
            pass = AT_PASS_ADD_CONSTR;
            break;
        case AT_AddIndexConstraint:     /* ADD CONSTRAINT USING INDEX */
            ATSimplePermissions(rel, ATT_TABLE);
            /* This command never recurses */
            /* No command-specific prep needed */
            pass = AT_PASS_ADD_CONSTR;
            break;
        case AT_DropConstraint: /* DROP CONSTRAINT */
            ATSimplePermissions(rel, ATT_TABLE);
            /* Recursion occurs during execution phase */
            /* No command-specific prep needed except saving recurse flag */
            if (recurse)
                cmd->subtype = AT_DropConstraintRecurse;
            pass = AT_PASS_DROP;
            break;
        case AT_AlterColumnType:        /* ALTER COLUMN TYPE */
            ATSimplePermissions(rel,
                         ATT_TABLE | ATT_COMPOSITE_TYPE | ATT_FOREIGN_TABLE);
            /* Performs own recursion */
            ATPrepAlterColumnType(wqueue, tab, rel, recurse, recursing, cmd, lockmode);
            pass = AT_PASS_ALTER_TYPE;
            break;
        case AT_AlterColumnGenericOptions:
            ATSimplePermissions(rel, ATT_FOREIGN_TABLE);
            /* This command never recurses */
            /* No command-specific prep needed */
            pass = AT_PASS_MISC;
            break;
        case AT_ChangeOwner:    /* ALTER OWNER */
            /* This command never recurses */
            /* No command-specific prep needed */
            pass = AT_PASS_MISC;
            break;
        case AT_ClusterOn:      /* CLUSTER ON */
        case AT_DropCluster:    /* SET WITHOUT CLUSTER */
            ATSimplePermissions(rel, ATT_TABLE | ATT_MATVIEW);
            /* These commands never recurse */
            /* No command-specific prep needed */
            pass = AT_PASS_MISC;
            break;
        case AT_AddOids:        /* SET WITH OIDS */
            ATSimplePermissions(rel, ATT_TABLE);
            if (!rel->rd_rel->relhasoids || recursing)
                ATPrepAddOids(wqueue, rel, recurse, cmd, lockmode);
            /* Recursion occurs during execution phase */
            pass = AT_PASS_ADD_COL;
            break;
        case AT_DropOids:       /* SET WITHOUT OIDS */
            ATSimplePermissions(rel, ATT_TABLE);
            /* Performs own recursion */
            if (rel->rd_rel->relhasoids)
            {
                AlterTableCmd *dropCmd = makeNode(AlterTableCmd);

                dropCmd->subtype = AT_DropColumn;
                dropCmd->name = pstrdup("oid");
                dropCmd->behavior = cmd->behavior;
                ATPrepCmd(wqueue, rel, dropCmd, recurse, false, lockmode);
            }
            pass = AT_PASS_DROP;
            break;
        case AT_SetTableSpace:  /* SET TABLESPACE */
            ATSimplePermissions(rel, ATT_TABLE | ATT_MATVIEW | ATT_INDEX);
            /* This command never recurses */
            ATPrepSetTableSpace(tab, rel, cmd->name, lockmode);
            pass = AT_PASS_MISC;    /* doesn't actually matter */
            break;
        case AT_SetRelOptions:  /* SET (...) */
        case AT_ResetRelOptions:        /* RESET (...) */
        case AT_ReplaceRelOptions:      /* reset them all, then set just these */
            ATSimplePermissions(rel, ATT_TABLE | ATT_VIEW | ATT_MATVIEW | ATT_INDEX);
            /* This command never recurses */
            /* No command-specific prep needed */
            pass = AT_PASS_MISC;
            break;
        case AT_AddInherit:     /* INHERIT */
            ATSimplePermissions(rel, ATT_TABLE);
            /* This command never recurses */
            ATPrepAddInherit(rel);
            pass = AT_PASS_MISC;
            break;
        case AT_ValidateConstraint:     /* VALIDATE CONSTRAINT */
            ATSimplePermissions(rel, ATT_TABLE);
            /* Recursion occurs during execution phase */
            /* No command-specific prep needed except saving recurse flag */
            if (recurse)
                cmd->subtype = AT_ValidateConstraintRecurse;
            pass = AT_PASS_MISC;
            break;
        case AT_EnableTrig:     /* ENABLE TRIGGER variants */
        case AT_EnableAlwaysTrig:
        case AT_EnableReplicaTrig:
        case AT_EnableTrigAll:
        case AT_EnableTrigUser:
        case AT_DisableTrig:    /* DISABLE TRIGGER variants */
        case AT_DisableTrigAll:
        case AT_DisableTrigUser:
        case AT_EnableRule:     /* ENABLE/DISABLE RULE variants */
        case AT_EnableAlwaysRule:
        case AT_EnableReplicaRule:
        case AT_DisableRule:
        case AT_DropInherit:    /* NO INHERIT */
        case AT_AddOf:          /* OF */
        case AT_DropOf: /* NOT OF */
            ATSimplePermissions(rel, ATT_TABLE);
            /* These commands never recurse */
            /* No command-specific prep needed */
            pass = AT_PASS_MISC;
            break;
        case AT_GenericOptions:
            ATSimplePermissions(rel, ATT_FOREIGN_TABLE);
            /* No command-specific prep needed */
            pass = AT_PASS_MISC;
            break;
        default:                /* oops */
            elog(ERROR, "unrecognized alter table type: %d",
                 (int) cmd->subtype);
            pass = 0;           /* keep compiler quiet */
            break;
    }

    /* Add the subcommand to the appropriate list for phase 2 */
    tab->subcmds[pass] = lappend(tab->subcmds[pass], cmd);
}

/*
 * ATRewriteCatalogs
 *
 * Traffic cop for ALTER TABLE Phase 2 operations.  Subcommands are
 * dispatched in a "safe" execution order (designed to avoid unnecessary
 * conflicts).
 */
static void
ATRewriteCatalogs(List **wqueue, LOCKMODE lockmode)
{
    int         pass;
    ListCell   *ltab;

    /*
     * We process all the tables "in parallel", one pass at a time.  This is
     * needed because we may have to propagate work from one table to another
     * (specifically, ALTER TYPE on a foreign key's PK has to dispatch the
     * re-adding of the foreign key constraint to the other table).  Work can
     * only be propagated into later passes, however.
     */
    for (pass = 0; pass < AT_NUM_PASSES; pass++)
    {
        /* Go through each table that needs to be processed */
        foreach(ltab, *wqueue)
        {
            AlteredTableInfo *tab = (AlteredTableInfo *) lfirst(ltab);
            List       *subcmds = tab->subcmds[pass];
            Relation    rel;
            ListCell   *lcmd;

            if (subcmds == NIL)
                continue;

            /*
             * Appropriate lock was obtained by phase 1, needn't get it again
             */
            rel = relation_open(tab->relid, NoLock);

            foreach(lcmd, subcmds)
                ATExecCmd(wqueue, tab, rel, (AlterTableCmd *) lfirst(lcmd), lockmode);

            /*
             * After the ALTER TYPE pass, do cleanup work (this is not done in
             * ATExecAlterColumnType since it should be done only once if
             * multiple columns of a table are altered).
             */
            if (pass == AT_PASS_ALTER_TYPE)
                ATPostAlterTypeCleanup(wqueue, tab, lockmode);

            relation_close(rel, NoLock);
        }
    }

    /* Check to see if a toast table must be added. */
    foreach(ltab, *wqueue)
    {
        AlteredTableInfo *tab = (AlteredTableInfo *) lfirst(ltab);

        if (tab->relkind == RELKIND_RELATION ||
            tab->relkind == RELKIND_MATVIEW)
            AlterTableCreateToastTable(tab->relid, (Datum) 0);
    }
}

/*
 * ATExecCmd: dispatch a subcommand to appropriate execution routine
 */
static void
ATExecCmd(List **wqueue, AlteredTableInfo *tab, Relation rel,
          AlterTableCmd *cmd, LOCKMODE lockmode)
{
    switch (cmd->subtype)
    {
        case AT_AddColumn:      /* ADD COLUMN */
        case AT_AddColumnToView:        /* add column via CREATE OR REPLACE
                                         * VIEW */
            ATExecAddColumn(wqueue, tab, rel, (ColumnDef *) cmd->def,
                            false, false, false, lockmode);
            break;
        case AT_AddColumnRecurse:
            ATExecAddColumn(wqueue, tab, rel, (ColumnDef *) cmd->def,
                            false, true, false, lockmode);
            break;
        case AT_ColumnDefault:  /* ALTER COLUMN DEFAULT */
            ATExecColumnDefault(rel, cmd->name, cmd->def, lockmode);
            break;
        case AT_DropNotNull:    /* ALTER COLUMN DROP NOT NULL */
            ATExecDropNotNull(rel, cmd->name, lockmode);
            break;
        case AT_SetNotNull:     /* ALTER COLUMN SET NOT NULL */
            ATExecSetNotNull(tab, rel, cmd->name, lockmode);
            break;
        case AT_SetStatistics:  /* ALTER COLUMN SET STATISTICS */
            ATExecSetStatistics(rel, cmd->name, cmd->def, lockmode);
            break;
        case AT_SetOptions:     /* ALTER COLUMN SET ( options ) */
            ATExecSetOptions(rel, cmd->name, cmd->def, false, lockmode);
            break;
        case AT_ResetOptions:   /* ALTER COLUMN RESET ( options ) */
            ATExecSetOptions(rel, cmd->name, cmd->def, true, lockmode);
            break;
        case AT_SetStorage:     /* ALTER COLUMN SET STORAGE */
            ATExecSetStorage(rel, cmd->name, cmd->def, lockmode);
            break;
        case AT_DropColumn:     /* DROP COLUMN */
            ATExecDropColumn(wqueue, rel, cmd->name,
                     cmd->behavior, false, false, cmd->missing_ok, lockmode);
            break;
        case AT_DropColumnRecurse:      /* DROP COLUMN with recursion */
            ATExecDropColumn(wqueue, rel, cmd->name,
                      cmd->behavior, true, false, cmd->missing_ok, lockmode);
            break;
        case AT_AddIndex:       /* ADD INDEX */
            ATExecAddIndex(tab, rel, (IndexStmt *) cmd->def, false, lockmode);
            break;
        case AT_ReAddIndex:     /* ADD INDEX */
            ATExecAddIndex(tab, rel, (IndexStmt *) cmd->def, true, lockmode);
            break;
        case AT_AddConstraint:  /* ADD CONSTRAINT */
            ATExecAddConstraint(wqueue, tab, rel, (Constraint *) cmd->def,
                                false, false, lockmode);
            break;
        case AT_AddConstraintRecurse:   /* ADD CONSTRAINT with recursion */
            ATExecAddConstraint(wqueue, tab, rel, (Constraint *) cmd->def,
                                true, false, lockmode);
            break;
        case AT_ReAddConstraint:    /* Re-add pre-existing check constraint */
            ATExecAddConstraint(wqueue, tab, rel, (Constraint *) cmd->def,
                                false, true, lockmode);
            break;
        case AT_AddIndexConstraint:     /* ADD CONSTRAINT USING INDEX */
            ATExecAddIndexConstraint(tab, rel, (IndexStmt *) cmd->def, lockmode);
            break;
        case AT_ValidateConstraint:     /* VALIDATE CONSTRAINT */
            ATExecValidateConstraint(rel, cmd->name, false, false, lockmode);
            break;
        case AT_ValidateConstraintRecurse:      /* VALIDATE CONSTRAINT with
                                                 * recursion */
            ATExecValidateConstraint(rel, cmd->name, true, false, lockmode);
            break;
        case AT_DropConstraint: /* DROP CONSTRAINT */
            ATExecDropConstraint(rel, cmd->name, cmd->behavior,
                                 false, false,
                                 cmd->missing_ok, lockmode);
            break;
        case AT_DropConstraintRecurse:  /* DROP CONSTRAINT with recursion */
            ATExecDropConstraint(rel, cmd->name, cmd->behavior,
                                 true, false,
                                 cmd->missing_ok, lockmode);
            break;
        case AT_AlterColumnType:        /* ALTER COLUMN TYPE */
            ATExecAlterColumnType(tab, rel, cmd, lockmode);
            break;
        case AT_AlterColumnGenericOptions:      /* ALTER COLUMN OPTIONS */
            ATExecAlterColumnGenericOptions(rel, cmd->name, (List *) cmd->def, lockmode);
            break;
        case AT_ChangeOwner:    /* ALTER OWNER */
            ATExecChangeOwner(RelationGetRelid(rel),
                              get_role_oid(cmd->name, false),
                              false, lockmode);
            break;
        case AT_ClusterOn:      /* CLUSTER ON */
            ATExecClusterOn(rel, cmd->name, lockmode);
            break;
        case AT_DropCluster:    /* SET WITHOUT CLUSTER */
            ATExecDropCluster(rel, lockmode);
            break;
        case AT_AddOids:        /* SET WITH OIDS */
            /* Use the ADD COLUMN code, unless prep decided to do nothing */
            if (cmd->def != NULL)
                ATExecAddColumn(wqueue, tab, rel, (ColumnDef *) cmd->def,
                                true, false, false, lockmode);
            break;
        case AT_AddOidsRecurse: /* SET WITH OIDS */
            /* Use the ADD COLUMN code, unless prep decided to do nothing */
            if (cmd->def != NULL)
                ATExecAddColumn(wqueue, tab, rel, (ColumnDef *) cmd->def,
                                true, true, false, lockmode);
            break;
        case AT_DropOids:       /* SET WITHOUT OIDS */

            /*
             * Nothing to do here; we'll have generated a DropColumn
             * subcommand to do the real work
             */
            break;
        case AT_SetTableSpace:  /* SET TABLESPACE */

            /*
             * Nothing to do here; Phase 3 does the work
             */
            break;
        case AT_SetRelOptions:  /* SET (...) */
        case AT_ResetRelOptions:        /* RESET (...) */
        case AT_ReplaceRelOptions:      /* replace entire option list */
            ATExecSetRelOptions(rel, (List *) cmd->def, cmd->subtype, lockmode);
            break;
        case AT_EnableTrig:     /* ENABLE TRIGGER name */
            ATExecEnableDisableTrigger(rel, cmd->name,
                                   TRIGGER_FIRES_ON_ORIGIN, false, lockmode);
            break;
        case AT_EnableAlwaysTrig:       /* ENABLE ALWAYS TRIGGER name */
            ATExecEnableDisableTrigger(rel, cmd->name,
                                       TRIGGER_FIRES_ALWAYS, false, lockmode);
            break;
        case AT_EnableReplicaTrig:      /* ENABLE REPLICA TRIGGER name */
            ATExecEnableDisableTrigger(rel, cmd->name,
                                  TRIGGER_FIRES_ON_REPLICA, false, lockmode);
            break;
        case AT_DisableTrig:    /* DISABLE TRIGGER name */
            ATExecEnableDisableTrigger(rel, cmd->name,
                                       TRIGGER_DISABLED, false, lockmode);
            break;
        case AT_EnableTrigAll:  /* ENABLE TRIGGER ALL */
            ATExecEnableDisableTrigger(rel, NULL,
                                   TRIGGER_FIRES_ON_ORIGIN, false, lockmode);
            break;
        case AT_DisableTrigAll: /* DISABLE TRIGGER ALL */
            ATExecEnableDisableTrigger(rel, NULL,
                                       TRIGGER_DISABLED, false, lockmode);
            break;
        case AT_EnableTrigUser: /* ENABLE TRIGGER USER */
            ATExecEnableDisableTrigger(rel, NULL,
                                    TRIGGER_FIRES_ON_ORIGIN, true, lockmode);
            break;
        case AT_DisableTrigUser:        /* DISABLE TRIGGER USER */
            ATExecEnableDisableTrigger(rel, NULL,
                                       TRIGGER_DISABLED, true, lockmode);
            break;

        case AT_EnableRule:     /* ENABLE RULE name */
            ATExecEnableDisableRule(rel, cmd->name,
                                    RULE_FIRES_ON_ORIGIN, lockmode);
            break;
        case AT_EnableAlwaysRule:       /* ENABLE ALWAYS RULE name */
            ATExecEnableDisableRule(rel, cmd->name,
                                    RULE_FIRES_ALWAYS, lockmode);
            break;
        case AT_EnableReplicaRule:      /* ENABLE REPLICA RULE name */
            ATExecEnableDisableRule(rel, cmd->name,
                                    RULE_FIRES_ON_REPLICA, lockmode);
            break;
        case AT_DisableRule:    /* DISABLE RULE name */
            ATExecEnableDisableRule(rel, cmd->name,
                                    RULE_DISABLED, lockmode);
            break;

        case AT_AddInherit:
            ATExecAddInherit(rel, (RangeVar *) cmd->def, lockmode);
            break;
        case AT_DropInherit:
            ATExecDropInherit(rel, (RangeVar *) cmd->def, lockmode);
            break;
        case AT_AddOf:
            ATExecAddOf(rel, (TypeName *) cmd->def, lockmode);
            break;
        case AT_DropOf:
            ATExecDropOf(rel, lockmode);
            break;
        case AT_GenericOptions:
            ATExecGenericOptions(rel, (List *) cmd->def);
            break;
        default:                /* oops */
            elog(ERROR, "unrecognized alter table type: %d",
                 (int) cmd->subtype);
            break;
    }

    /*
     * Bump the command counter to ensure the next subcommand in the sequence
     * can see the changes so far
     */
    CommandCounterIncrement();
}

/*
 * ATRewriteTables: ALTER TABLE phase 3
 */
static void
ATRewriteTables(List **wqueue, LOCKMODE lockmode)
{
    ListCell   *ltab;

    /* Go through each table that needs to be checked or rewritten */
    foreach(ltab, *wqueue)
    {
        AlteredTableInfo *tab = (AlteredTableInfo *) lfirst(ltab);

        /* Foreign tables have no storage. */
        if (tab->relkind == RELKIND_FOREIGN_TABLE)
            continue;

        /*
         * If we change column data types or add/remove OIDs, the operation
         * has to be propagated to tables that use this table's rowtype as a
         * column type.  tab->newvals will also be non-NULL in the case where
         * we're adding a column with a default.  We choose to forbid that
         * case as well, since composite types might eventually support
         * defaults.
         *
         * (Eventually we'll probably need to check for composite type
         * dependencies even when we're just scanning the table without a
         * rewrite, but at the moment a composite type does not enforce any
         * constraints, so it's not necessary/appropriate to enforce them just
         * during ALTER.)
         */
        if (tab->newvals != NIL || tab->rewrite)
        {
            Relation    rel;

            rel = heap_open(tab->relid, NoLock);
            find_composite_type_dependencies(rel->rd_rel->reltype, rel, NULL);
            heap_close(rel, NoLock);
        }

        /*
         * We only need to rewrite the table if at least one column needs to
         * be recomputed, or we are adding/removing the OID column.
         */
        if (tab->rewrite)
        {
            /* Build a temporary relation and copy data */
            Relation    OldHeap;
            Oid         OIDNewHeap;
            Oid         NewTableSpace;

            OldHeap = heap_open(tab->relid, NoLock);

            /*
             * We don't support rewriting of system catalogs; there are too
             * many corner cases and too little benefit.  In particular this
             * is certainly not going to work for mapped catalogs.
             */
            if (IsSystemRelation(OldHeap))
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("cannot rewrite system relation \"%s\"",
                                RelationGetRelationName(OldHeap))));

            /*
             * Don't allow rewrite on temp tables of other backends ... their
             * local buffer manager is not going to cope.
             */
            if (RELATION_IS_OTHER_TEMP(OldHeap))
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                errmsg("cannot rewrite temporary tables of other sessions")));

            /*
             * Select destination tablespace (same as original unless user
             * requested a change)
             */
            if (tab->newTableSpace)
                NewTableSpace = tab->newTableSpace;
            else
                NewTableSpace = OldHeap->rd_rel->reltablespace;

            heap_close(OldHeap, NoLock);

            /* Create transient table that will receive the modified data */
            OIDNewHeap = make_new_heap(tab->relid, NewTableSpace);

            /*
             * Copy the heap data into the new table with the desired
             * modifications, and test the current data within the table
             * against new constraints generated by ALTER TABLE commands.
             */
            ATRewriteTable(tab, OIDNewHeap, lockmode);

            /*
             * Swap the physical files of the old and new heaps, then rebuild
             * indexes and discard the old heap.  We can use RecentXmin for
             * the table's new relfrozenxid because we rewrote all the tuples
             * in ATRewriteTable, so no older Xid remains in the table.  Also,
             * we never try to swap toast tables by content, since we have no
             * interest in letting this code work on system catalogs.
             */
            finish_heap_swap(tab->relid, OIDNewHeap,
                             false, false, true,
                             !OidIsValid(tab->newTableSpace),
                             RecentXmin,
                             ReadNextMultiXactId());
        }
        else
        {
            /*
             * Test the current data within the table against new constraints
             * generated by ALTER TABLE commands, but don't rebuild data.
             */
            if (tab->constraints != NIL || tab->new_notnull)
                ATRewriteTable(tab, InvalidOid, lockmode);

            /*
             * If we had SET TABLESPACE but no reason to reconstruct tuples,
             * just do a block-by-block copy.
             */
            if (tab->newTableSpace)
                ATExecSetTableSpace(tab->relid, tab->newTableSpace, lockmode);
        }
    }

    /*
     * Foreign key constraints are checked in a final pass, since (a) it's
     * generally best to examine each one separately, and (b) it's at least
     * theoretically possible that we have changed both relations of the
     * foreign key, and we'd better have finished both rewrites before we try
     * to read the tables.
     */
    foreach(ltab, *wqueue)
    {
        AlteredTableInfo *tab = (AlteredTableInfo *) lfirst(ltab);
        Relation    rel = NULL;
        ListCell   *lcon;

        foreach(lcon, tab->constraints)
        {
            NewConstraint *con = lfirst(lcon);

            if (con->contype == CONSTR_FOREIGN)
            {
                Constraint *fkconstraint = (Constraint *) con->qual;
                Relation    refrel;

                if (rel == NULL)
                {
                    /* Long since locked, no need for another */
                    rel = heap_open(tab->relid, NoLock);
                }

                refrel = heap_open(con->refrelid, RowShareLock);

                validateForeignKeyConstraint(fkconstraint->conname, rel, refrel,
                                             con->refindid,
                                             con->conid);

                /*
                 * No need to mark the constraint row as validated, we did
                 * that when we inserted the row earlier.
                 */

                heap_close(refrel, NoLock);
            }
        }

        if (rel)
            heap_close(rel, NoLock);
    }
}

/*
 * ATRewriteTable: scan or rewrite one table
 *
 * OIDNewHeap is InvalidOid if we don't need to rewrite
 */
static void
ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
{
    Relation    oldrel;
    Relation    newrel;
    TupleDesc   oldTupDesc;
    TupleDesc   newTupDesc;
    bool        needscan = false;
    List       *notnull_attrs;
    int         i;
    ListCell   *l;
    EState     *estate;
    CommandId   mycid;
    BulkInsertState bistate;
    int         hi_options;

    /*
     * Open the relation(s).  We have surely already locked the existing
     * table.
     */
    oldrel = heap_open(tab->relid, NoLock);
    oldTupDesc = tab->oldDesc;
    newTupDesc = RelationGetDescr(oldrel);      /* includes all mods */

    if (OidIsValid(OIDNewHeap))
        newrel = heap_open(OIDNewHeap, lockmode);
    else
        newrel = NULL;

    /*
     * Prepare a BulkInsertState and options for heap_insert. Because we're
     * building a new heap, we can skip WAL-logging and fsync it to disk at
     * the end instead (unless WAL-logging is required for archiving or
     * streaming replication). The FSM is empty too, so don't bother using it.
     */
    if (newrel)
    {
        mycid = GetCurrentCommandId(true);
        bistate = GetBulkInsertState();

        hi_options = HEAP_INSERT_SKIP_FSM;
        if (!XLogIsNeeded())
            hi_options |= HEAP_INSERT_SKIP_WAL;
    }
    else
    {
        /* keep compiler quiet about using these uninitialized */
        mycid = 0;
        bistate = NULL;
        hi_options = 0;
    }

    /*
     * Generate the constraint and default execution states
     */

    estate = CreateExecutorState();

    /* Build the needed expression execution states */
    foreach(l, tab->constraints)
    {
        NewConstraint *con = lfirst(l);

        switch (con->contype)
        {
            case CONSTR_CHECK:
                needscan = true;
                con->qualstate = (List *)
                    ExecPrepareExpr((Expr *) con->qual, estate);
                break;
            case CONSTR_FOREIGN:
                /* Nothing to do here */
                break;
            default:
                elog(ERROR, "unrecognized constraint type: %d",
                     (int) con->contype);
        }
    }

    foreach(l, tab->newvals)
    {
        NewColumnValue *ex = lfirst(l);

        /* expr already planned */
        ex->exprstate = ExecInitExpr((Expr *) ex->expr, NULL);
    }

    notnull_attrs = NIL;
    if (newrel || tab->new_notnull)
    {
        /*
         * If we are rebuilding the tuples OR if we added any new NOT NULL
         * constraints, check all not-null constraints.  This is a bit of
         * overkill but it minimizes risk of bugs, and heap_attisnull is a
         * pretty cheap test anyway.
         */
        for (i = 0; i < newTupDesc->natts; i++)
        {
            if (newTupDesc->attrs[i]->attnotnull &&
                !newTupDesc->attrs[i]->attisdropped)
                notnull_attrs = lappend_int(notnull_attrs, i);
        }
        if (notnull_attrs)
            needscan = true;
    }

    if (newrel || needscan)
    {
        ExprContext *econtext;
        Datum      *values;
        bool       *isnull;
        TupleTableSlot *oldslot;
        TupleTableSlot *newslot;
        HeapScanDesc scan;
        HeapTuple   tuple;
        MemoryContext oldCxt;
        List       *dropped_attrs = NIL;
        ListCell   *lc;

        if (newrel)
            ereport(DEBUG1,
                    (errmsg("rewriting table \"%s\"",
                            RelationGetRelationName(oldrel))));
        else
            ereport(DEBUG1,
                    (errmsg("verifying table \"%s\"",
                            RelationGetRelationName(oldrel))));

        if (newrel)
        {
            /*
             * All predicate locks on the tuples or pages are about to be made
             * invalid, because we move tuples around.  Promote them to
             * relation locks.
             */
            TransferPredicateLocksToHeapRelation(oldrel);
        }

        econtext = GetPerTupleExprContext(estate);

        /*
         * Make tuple slots for old and new tuples.  Note that even when the
         * tuples are the same, the tupDescs might not be (consider ADD COLUMN
         * without a default).
         */
        oldslot = MakeSingleTupleTableSlot(oldTupDesc);
        newslot = MakeSingleTupleTableSlot(newTupDesc);

        /* Preallocate values/isnull arrays */
        i = Max(newTupDesc->natts, oldTupDesc->natts);
        values = (Datum *) palloc(i * sizeof(Datum));
        isnull = (bool *) palloc(i * sizeof(bool));
        memset(values, 0, i * sizeof(Datum));
        memset(isnull, true, i * sizeof(bool));

        /*
         * Any attributes that are dropped according to the new tuple
         * descriptor can be set to NULL. We precompute the list of dropped
         * attributes to avoid needing to do so in the per-tuple loop.
         */
        for (i = 0; i < newTupDesc->natts; i++)
        {
            if (newTupDesc->attrs[i]->attisdropped)
                dropped_attrs = lappend_int(dropped_attrs, i);
        }

        /*
         * Scan through the rows, generating a new row if needed and then
         * checking all the constraints.
         */
        scan = heap_beginscan(oldrel, SnapshotNow, 0, NULL);

        /*
         * Switch to per-tuple memory context and reset it for each tuple
         * produced, so we don't leak memory.
         */
        oldCxt = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));

        while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
        {
            if (tab->rewrite)
            {
                Oid         tupOid = InvalidOid;

                /* Extract data from old tuple */
                heap_deform_tuple(tuple, oldTupDesc, values, isnull);
                if (oldTupDesc->tdhasoid)
                    tupOid = HeapTupleGetOid(tuple);

                /* Set dropped attributes to null in new tuple */
                foreach(lc, dropped_attrs)
                    isnull[lfirst_int(lc)] = true;

                /*
                 * Process supplied expressions to replace selected columns.
                 * Expression inputs come from the old tuple.
                 */
                ExecStoreTuple(tuple, oldslot, InvalidBuffer, false);
                econtext->ecxt_scantuple = oldslot;

                foreach(l, tab->newvals)
                {
                    NewColumnValue *ex = lfirst(l);

                    values[ex->attnum - 1] = ExecEvalExpr(ex->exprstate,
                                                          econtext,
                                                     &isnull[ex->attnum - 1],
                                                          NULL);
                }

                /*
                 * Form the new tuple. Note that we don't explicitly pfree it,
                 * since the per-tuple memory context will be reset shortly.
                 */
                tuple = heap_form_tuple(newTupDesc, values, isnull);

                /* Preserve OID, if any */
                if (newTupDesc->tdhasoid)
                    HeapTupleSetOid(tuple, tupOid);
            }

            /* Now check any constraints on the possibly-changed tuple */
            ExecStoreTuple(tuple, newslot, InvalidBuffer, false);
            econtext->ecxt_scantuple = newslot;

            foreach(l, notnull_attrs)
            {
                int         attn = lfirst_int(l);

                if (heap_attisnull(tuple, attn + 1))
                    ereport(ERROR,
                            (errcode(ERRCODE_NOT_NULL_VIOLATION),
                             errmsg("column \"%s\" contains null values",
                                NameStr(newTupDesc->attrs[attn]->attname)),
                             errtablecol(oldrel, attn + 1)));
            }

            foreach(l, tab->constraints)
            {
                NewConstraint *con = lfirst(l);

                switch (con->contype)
                {
                    case CONSTR_CHECK:
                        if (!ExecQual(con->qualstate, econtext, true))
                            ereport(ERROR,
                                    (errcode(ERRCODE_CHECK_VIOLATION),
                                     errmsg("check constraint \"%s\" is violated by some row",
                                            con->name),
                                     errtableconstraint(oldrel, con->name)));
                        break;
                    case CONSTR_FOREIGN:
                        /* Nothing to do here */
                        break;
                    default:
                        elog(ERROR, "unrecognized constraint type: %d",
                             (int) con->contype);
                }
            }

            /* Write the tuple out to the new relation */
            if (newrel)
                heap_insert(newrel, tuple, mycid, hi_options, bistate);

            ResetExprContext(econtext);

            CHECK_FOR_INTERRUPTS();
        }

        MemoryContextSwitchTo(oldCxt);
        heap_endscan(scan);

        ExecDropSingleTupleTableSlot(oldslot);
        ExecDropSingleTupleTableSlot(newslot);
    }

    FreeExecutorState(estate);

    heap_close(oldrel, NoLock);
    if (newrel)
    {
        FreeBulkInsertState(bistate);

        /* If we skipped writing WAL, then we need to sync the heap. */
        if (hi_options & HEAP_INSERT_SKIP_WAL)
            heap_sync(newrel);

        heap_close(newrel, NoLock);
    }
}

/*
 * ATGetQueueEntry: find or create an entry in the ALTER TABLE work queue
 */
static AlteredTableInfo *
ATGetQueueEntry(List **wqueue, Relation rel)
{
    Oid         relid = RelationGetRelid(rel);
    AlteredTableInfo *tab;
    ListCell   *ltab;

    foreach(ltab, *wqueue)
    {
        tab = (AlteredTableInfo *) lfirst(ltab);
        if (tab->relid == relid)
            return tab;
    }

    /*
     * Not there, so add it.  Note that we make a copy of the relation's
     * existing descriptor before anything interesting can happen to it.
     */
    tab = (AlteredTableInfo *) palloc0(sizeof(AlteredTableInfo));
    tab->relid = relid;
    tab->relkind = rel->rd_rel->relkind;
    tab->oldDesc = CreateTupleDescCopy(RelationGetDescr(rel));

    *wqueue = lappend(*wqueue, tab);

    return tab;
}

/*
 * ATSimplePermissions
 *
 * - Ensure that it is a relation (or possibly a view)
 * - Ensure this user is the owner
 * - Ensure that it is not a system table
 */
static void
ATSimplePermissions(Relation rel, int allowed_targets)
{
    int         actual_target;

    switch (rel->rd_rel->relkind)
    {
        case RELKIND_RELATION:
            actual_target = ATT_TABLE;
            break;
        case RELKIND_VIEW:
            actual_target = ATT_VIEW;
            break;
        case RELKIND_MATVIEW:
            actual_target = ATT_MATVIEW;
            break;
        case RELKIND_INDEX:
            actual_target = ATT_INDEX;
            break;
        case RELKIND_COMPOSITE_TYPE:
            actual_target = ATT_COMPOSITE_TYPE;
            break;
        case RELKIND_FOREIGN_TABLE:
            actual_target = ATT_FOREIGN_TABLE;
            break;
        default:
            actual_target = 0;
            break;
    }

    /* Wrong target type? */
    if ((actual_target & allowed_targets) == 0)
        ATWrongRelkindError(rel, allowed_targets);

    /* Permissions checks */
    if (!pg_class_ownercheck(RelationGetRelid(rel), GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
                       RelationGetRelationName(rel));

    if (!allowSystemTableMods && IsSystemRelation(rel))
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied: \"%s\" is a system catalog",
                        RelationGetRelationName(rel))));
}

/*
 * ATWrongRelkindError
 *
 * Throw an error when a relation has been determined to be of the wrong
 * type.
 */
static void
ATWrongRelkindError(Relation rel, int allowed_targets)
{
    char       *msg;

    switch (allowed_targets)
    {
        case ATT_TABLE:
            msg = _("\"%s\" is not a table");
            break;
        case ATT_TABLE | ATT_VIEW:
            msg = _("\"%s\" is not a table or view");
            break;
        case ATT_TABLE | ATT_VIEW | ATT_MATVIEW | ATT_INDEX:
            msg = _("\"%s\" is not a table, view, materialized view, or index");
            break;
        case ATT_TABLE | ATT_MATVIEW:
            msg = _("\"%s\" is not a table or materialized view");
            break;
        case ATT_TABLE | ATT_MATVIEW | ATT_INDEX:
            msg = _("\"%s\" is not a table, materialized view, or index");
            break;
        case ATT_TABLE | ATT_FOREIGN_TABLE:
            msg = _("\"%s\" is not a table or foreign table");
            break;
        case ATT_TABLE | ATT_COMPOSITE_TYPE | ATT_FOREIGN_TABLE:
            msg = _("\"%s\" is not a table, composite type, or foreign table");
            break;
        case ATT_TABLE | ATT_MATVIEW | ATT_INDEX | ATT_FOREIGN_TABLE:
            msg = _("\"%s\" is not a table, materialized view, composite type, or foreign table");
            break;
        case ATT_VIEW:
            msg = _("\"%s\" is not a view");
            break;
        case ATT_FOREIGN_TABLE:
            msg = _("\"%s\" is not a foreign table");
            break;
        default:
            /* shouldn't get here, add all necessary cases above */
            msg = _("\"%s\" is of the wrong type");
            break;
    }

    ereport(ERROR,
            (errcode(ERRCODE_WRONG_OBJECT_TYPE),
             errmsg(msg, RelationGetRelationName(rel))));
}

/*
 * ATSimpleRecursion
 *
 * Simple table recursion sufficient for most ALTER TABLE operations.
 * All direct and indirect children are processed in an unspecified order.
 * Note that if a child inherits from the original table via multiple
 * inheritance paths, it will be visited just once.
 */
static void
ATSimpleRecursion(List **wqueue, Relation rel,
                  AlterTableCmd *cmd, bool recurse, LOCKMODE lockmode)
{
    /*
     * Propagate to children if desired.  Non-table relations never have
     * children, so no need to search in that case.
     */
    if (recurse && rel->rd_rel->relkind == RELKIND_RELATION)
    {
        Oid         relid = RelationGetRelid(rel);
        ListCell   *child;
        List       *children;

        children = find_all_inheritors(relid, lockmode, NULL);

        /*
         * find_all_inheritors does the recursive search of the inheritance
         * hierarchy, so all we have to do is process all of the relids in the
         * list that it returns.
         */
        foreach(child, children)
        {
            Oid         childrelid = lfirst_oid(child);
            Relation    childrel;

            if (childrelid == relid)
                continue;
            /* find_all_inheritors already got lock */
            childrel = relation_open(childrelid, NoLock);
            CheckTableNotInUse(childrel, "ALTER TABLE");
            ATPrepCmd(wqueue, childrel, cmd, false, true, lockmode);
            relation_close(childrel, NoLock);
        }
    }
}

/*
 * ATTypedTableRecursion
 *
 * Propagate ALTER TYPE operations to the typed tables of that type.
 * Also check the RESTRICT/CASCADE behavior.  Given CASCADE, also permit
 * recursion to inheritance children of the typed tables.
 */
static void
ATTypedTableRecursion(List **wqueue, Relation rel, AlterTableCmd *cmd,
                      LOCKMODE lockmode)
{
    ListCell   *child;
    List       *children;

    Assert(rel->rd_rel->relkind == RELKIND_COMPOSITE_TYPE);

    children = find_typed_table_dependencies(rel->rd_rel->reltype,
                                             RelationGetRelationName(rel),
                                             cmd->behavior);

    foreach(child, children)
    {
        Oid         childrelid = lfirst_oid(child);
        Relation    childrel;

        childrel = relation_open(childrelid, lockmode);
        CheckTableNotInUse(childrel, "ALTER TABLE");
        ATPrepCmd(wqueue, childrel, cmd, true, true, lockmode);
        relation_close(childrel, NoLock);
    }
}


/*
 * find_composite_type_dependencies
 *
 * Check to see if a composite type is being used as a column in some
 * other table (possibly nested several levels deep in composite types!).
 * Eventually, we'd like to propagate the check or rewrite operation
 * into other such tables, but for now, just error out if we find any.
 *
 * Caller should provide either a table name or a type name (not both) to
 * report in the error message, if any.
 *
 * We assume that functions and views depending on the type are not reasons
 * to reject the ALTER.  (How safe is this really?)
 */
void
find_composite_type_dependencies(Oid typeOid, Relation origRelation,
                                 const char *origTypeName)
{
    Relation    depRel;
    ScanKeyData key[2];
    SysScanDesc depScan;
    HeapTuple   depTup;
    Oid         arrayOid;

    /*
     * We scan pg_depend to find those things that depend on the rowtype. (We
     * assume we can ignore refobjsubid for a rowtype.)
     */
    depRel = heap_open(DependRelationId, AccessShareLock);

    ScanKeyInit(&key[0],
                Anum_pg_depend_refclassid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(TypeRelationId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_refobjid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(typeOid));

    depScan = systable_beginscan(depRel, DependReferenceIndexId, true,
                                 SnapshotNow, 2, key);

    while (HeapTupleIsValid(depTup = systable_getnext(depScan)))
    {
        Form_pg_depend pg_depend = (Form_pg_depend) GETSTRUCT(depTup);
        Relation    rel;
        Form_pg_attribute att;

        /* Ignore dependees that aren't user columns of relations */
        /* (we assume system columns are never of rowtypes) */
        if (pg_depend->classid != RelationRelationId ||
            pg_depend->objsubid <= 0)
            continue;

        rel = relation_open(pg_depend->objid, AccessShareLock);
        att = rel->rd_att->attrs[pg_depend->objsubid - 1];

        if (rel->rd_rel->relkind == RELKIND_RELATION ||
            rel->rd_rel->relkind == RELKIND_MATVIEW)
        {
            if (origTypeName)
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("cannot alter type \"%s\" because column \"%s.%s\" uses it",
                                origTypeName,
                                RelationGetRelationName(rel),
                                NameStr(att->attname))));
            else if (origRelation->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("cannot alter type \"%s\" because column \"%s.%s\" uses it",
                                RelationGetRelationName(origRelation),
                                RelationGetRelationName(rel),
                                NameStr(att->attname))));
            else if (origRelation->rd_rel->relkind == RELKIND_FOREIGN_TABLE)
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("cannot alter foreign table \"%s\" because column \"%s.%s\" uses its row type",
                                RelationGetRelationName(origRelation),
                                RelationGetRelationName(rel),
                                NameStr(att->attname))));
            else
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("cannot alter table \"%s\" because column \"%s.%s\" uses its row type",
                                RelationGetRelationName(origRelation),
                                RelationGetRelationName(rel),
                                NameStr(att->attname))));
        }
        else if (OidIsValid(rel->rd_rel->reltype))
        {
            /*
             * A view or composite type itself isn't a problem, but we must
             * recursively check for indirect dependencies via its rowtype.
             */
            find_composite_type_dependencies(rel->rd_rel->reltype,
                                             origRelation, origTypeName);
        }

        relation_close(rel, AccessShareLock);
    }

    systable_endscan(depScan);

    relation_close(depRel, AccessShareLock);

    /*
     * If there's an array type for the rowtype, must check for uses of it,
     * too.
     */
    arrayOid = get_array_type(typeOid);
    if (OidIsValid(arrayOid))
        find_composite_type_dependencies(arrayOid, origRelation, origTypeName);
}


/*
 * find_typed_table_dependencies
 *
 * Check to see if a composite type is being used as the type of a
 * typed table.  Abort if any are found and behavior is RESTRICT.
 * Else return the list of tables.
 */
static List *
find_typed_table_dependencies(Oid typeOid, const char *typeName, DropBehavior behavior)
{
    Relation    classRel;
    ScanKeyData key[1];
    HeapScanDesc scan;
    HeapTuple   tuple;
    List       *result = NIL;

    classRel = heap_open(RelationRelationId, AccessShareLock);

    ScanKeyInit(&key[0],
                Anum_pg_class_reloftype,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(typeOid));

    scan = heap_beginscan(classRel, SnapshotNow, 1, key);

    while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
    {
        if (behavior == DROP_RESTRICT)
            ereport(ERROR,
                    (errcode(ERRCODE_DEPENDENT_OBJECTS_STILL_EXIST),
                     errmsg("cannot alter type \"%s\" because it is the type of a typed table",
                            typeName),
            errhint("Use ALTER ... CASCADE to alter the typed tables too.")));
        else
            result = lappend_oid(result, HeapTupleGetOid(tuple));
    }

    heap_endscan(scan);
    heap_close(classRel, AccessShareLock);

    return result;
}


/*
 * check_of_type
 *
 * Check whether a type is suitable for CREATE TABLE OF/ALTER TABLE OF.  If it
 * isn't suitable, throw an error.  Currently, we require that the type
 * originated with CREATE TYPE AS.  We could support any row type, but doing so
 * would require handling a number of extra corner cases in the DDL commands.
 */
void
check_of_type(HeapTuple typetuple)
{
    Form_pg_type typ = (Form_pg_type) GETSTRUCT(typetuple);
    bool        typeOk = false;

    if (typ->typtype == TYPTYPE_COMPOSITE)
    {
        Relation    typeRelation;

        Assert(OidIsValid(typ->typrelid));
        typeRelation = relation_open(typ->typrelid, AccessShareLock);
        typeOk = (typeRelation->rd_rel->relkind == RELKIND_COMPOSITE_TYPE);

        /*
         * Close the parent rel, but keep our AccessShareLock on it until xact
         * commit.  That will prevent someone else from deleting or ALTERing
         * the type before the typed table creation/conversion commits.
         */
        relation_close(typeRelation, NoLock);
    }
    if (!typeOk)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("type %s is not a composite type",
                        format_type_be(HeapTupleGetOid(typetuple)))));
}


/*
 * ALTER TABLE ADD COLUMN
 *
 * Adds an additional attribute to a relation making the assumption that
 * CHECK, NOT NULL, and FOREIGN KEY constraints will be removed from the
 * AT_AddColumn AlterTableCmd by parse_utilcmd.c and added as independent
 * AlterTableCmd's.
 *
 * ADD COLUMN cannot use the normal ALTER TABLE recursion mechanism, because we
 * have to decide at runtime whether to recurse or not depending on whether we
 * actually add a column or merely merge with an existing column.  (We can't
 * check this in a static pre-pass because it won't handle multiple inheritance
 * situations correctly.)
 */
static void
ATPrepAddColumn(List **wqueue, Relation rel, bool recurse, bool recursing,
                AlterTableCmd *cmd, LOCKMODE lockmode)
{
    if (rel->rd_rel->reloftype && !recursing)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("cannot add column to typed table")));

    if (rel->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
        ATTypedTableRecursion(wqueue, rel, cmd, lockmode);

    if (recurse)
        cmd->subtype = AT_AddColumnRecurse;
}

static void
ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
                ColumnDef *colDef, bool isOid,
                bool recurse, bool recursing, LOCKMODE lockmode)
{
    Oid         myrelid = RelationGetRelid(rel);
    Relation    pgclass,
                attrdesc;
    HeapTuple   reltup;
    FormData_pg_attribute attribute;
    int         newattnum;
    char        relkind;
    HeapTuple   typeTuple;
    Oid         typeOid;
    int32       typmod;
    Oid         collOid;
    Form_pg_type tform;
    Expr       *defval;
    List       *children;
    ListCell   *child;
    AclResult   aclresult;

    /* At top level, permission check was done in ATPrepCmd, else do it */
    if (recursing)
        ATSimplePermissions(rel, ATT_TABLE);

    attrdesc = heap_open(AttributeRelationId, RowExclusiveLock);

    /*
     * Are we adding the column to a recursion child?  If so, check whether to
     * merge with an existing definition for the column.  If we do merge, we
     * must not recurse.  Children will already have the column, and recursing
     * into them would mess up attinhcount.
     */
    if (colDef->inhcount > 0)
    {
        HeapTuple   tuple;

        /* Does child already have a column by this name? */
        tuple = SearchSysCacheCopyAttName(myrelid, colDef->colname);
        if (HeapTupleIsValid(tuple))
        {
            Form_pg_attribute childatt = (Form_pg_attribute) GETSTRUCT(tuple);
            Oid         ctypeId;
            int32       ctypmod;
            Oid         ccollid;

            /* Child column must match on type, typmod, and collation */
            typenameTypeIdAndMod(NULL, colDef->typeName, &ctypeId, &ctypmod);
            if (ctypeId != childatt->atttypid ||
                ctypmod != childatt->atttypmod)
                ereport(ERROR,
                        (errcode(ERRCODE_DATATYPE_MISMATCH),
                         errmsg("child table \"%s\" has different type for column \"%s\"",
                            RelationGetRelationName(rel), colDef->colname)));
            ccollid = GetColumnDefCollation(NULL, colDef, ctypeId);
            if (ccollid != childatt->attcollation)
                ereport(ERROR,
                        (errcode(ERRCODE_COLLATION_MISMATCH),
                         errmsg("child table \"%s\" has different collation for column \"%s\"",
                              RelationGetRelationName(rel), colDef->colname),
                         errdetail("\"%s\" versus \"%s\"",
                                   get_collation_name(ccollid),
                               get_collation_name(childatt->attcollation))));

            /* If it's OID, child column must actually be OID */
            if (isOid && childatt->attnum != ObjectIdAttributeNumber)
                ereport(ERROR,
                        (errcode(ERRCODE_DATATYPE_MISMATCH),
                 errmsg("child table \"%s\" has a conflicting \"%s\" column",
                        RelationGetRelationName(rel), colDef->colname)));

            /* Bump the existing child att's inhcount */
            childatt->attinhcount++;
            simple_heap_update(attrdesc, &tuple->t_self, tuple);
            CatalogUpdateIndexes(attrdesc, tuple);

            heap_freetuple(tuple);

            /* Inform the user about the merge */
            ereport(NOTICE,
              (errmsg("merging definition of column \"%s\" for child \"%s\"",
                      colDef->colname, RelationGetRelationName(rel))));

            heap_close(attrdesc, RowExclusiveLock);
            return;
        }
    }

    pgclass = heap_open(RelationRelationId, RowExclusiveLock);

    reltup = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(myrelid));
    if (!HeapTupleIsValid(reltup))
        elog(ERROR, "cache lookup failed for relation %u", myrelid);
    relkind = ((Form_pg_class) GETSTRUCT(reltup))->relkind;

    /* new name should not already exist */
    check_for_column_name_collision(rel, colDef->colname);

    /* Determine the new attribute's number */
    if (isOid)
        newattnum = ObjectIdAttributeNumber;
    else
    {
        newattnum = ((Form_pg_class) GETSTRUCT(reltup))->relnatts + 1;
        if (newattnum > MaxHeapAttributeNumber)
            ereport(ERROR,
                    (errcode(ERRCODE_TOO_MANY_COLUMNS),
                     errmsg("tables can have at most %d columns",
                            MaxHeapAttributeNumber)));
    }

    typeTuple = typenameType(NULL, colDef->typeName, &typmod);
    tform = (Form_pg_type) GETSTRUCT(typeTuple);
    typeOid = HeapTupleGetOid(typeTuple);

    aclresult = pg_type_aclcheck(typeOid, GetUserId(), ACL_USAGE);
    if (aclresult != ACLCHECK_OK)
        aclcheck_error_type(aclresult, typeOid);

    collOid = GetColumnDefCollation(NULL, colDef, typeOid);

    /* make sure datatype is legal for a column */
    CheckAttributeType(colDef->colname, typeOid, collOid,
                       list_make1_oid(rel->rd_rel->reltype),
                       false);

    /* construct new attribute's pg_attribute entry */
    attribute.attrelid = myrelid;
    namestrcpy(&(attribute.attname), colDef->colname);
    attribute.atttypid = typeOid;
    attribute.attstattarget = (newattnum > 0) ? -1 : 0;
    attribute.attlen = tform->typlen;
    attribute.attcacheoff = -1;
    attribute.atttypmod = typmod;
    attribute.attnum = newattnum;
    attribute.attbyval = tform->typbyval;
    attribute.attndims = list_length(colDef->typeName->arrayBounds);
    attribute.attstorage = tform->typstorage;
    attribute.attalign = tform->typalign;
    attribute.attnotnull = colDef->is_not_null;
    attribute.atthasdef = false;
    attribute.attisdropped = false;
    attribute.attislocal = colDef->is_local;
    attribute.attinhcount = colDef->inhcount;
    attribute.attcollation = collOid;
    /* attribute.attacl is handled by InsertPgAttributeTuple */

    ReleaseSysCache(typeTuple);

    InsertPgAttributeTuple(attrdesc, &attribute, NULL);

    heap_close(attrdesc, RowExclusiveLock);

    /*
     * Update pg_class tuple as appropriate
     */
    if (isOid)
        ((Form_pg_class) GETSTRUCT(reltup))->relhasoids = true;
    else
        ((Form_pg_class) GETSTRUCT(reltup))->relnatts = newattnum;

    simple_heap_update(pgclass, &reltup->t_self, reltup);

    /* keep catalog indexes current */
    CatalogUpdateIndexes(pgclass, reltup);

    heap_freetuple(reltup);

    /* Post creation hook for new attribute */
    InvokeObjectPostCreateHook(RelationRelationId, myrelid, newattnum);

    heap_close(pgclass, RowExclusiveLock);

    /* Make the attribute's catalog entry visible */
    CommandCounterIncrement();

    /*
     * Store the DEFAULT, if any, in the catalogs
     */
    if (colDef->raw_default)
    {
        RawColumnDefault *rawEnt;

        rawEnt = (RawColumnDefault *) palloc(sizeof(RawColumnDefault));
        rawEnt->attnum = attribute.attnum;
        rawEnt->raw_default = copyObject(colDef->raw_default);

        /*
         * This function is intended for CREATE TABLE, so it processes a
         * _list_ of defaults, but we just do one.
         */
        AddRelationNewConstraints(rel, list_make1(rawEnt), NIL,
                                  false, true, false);

        /* Make the additional catalog changes visible */
        CommandCounterIncrement();
    }

    /*
     * Tell Phase 3 to fill in the default expression, if there is one.
     *
     * If there is no default, Phase 3 doesn't have to do anything, because
     * that effectively means that the default is NULL.  The heap tuple access
     * routines always check for attnum > # of attributes in tuple, and return
     * NULL if so, so without any modification of the tuple data we will get
     * the effect of NULL values in the new column.
     *
     * An exception occurs when the new column is of a domain type: the domain
     * might have a NOT NULL constraint, or a check constraint that indirectly
     * rejects nulls.  If there are any domain constraints then we construct
     * an explicit NULL default value that will be passed through
     * CoerceToDomain processing.  (This is a tad inefficient, since it causes
     * rewriting the table which we really don't have to do, but the present
     * design of domain processing doesn't offer any simple way of checking
     * the constraints more directly.)
     *
     * Note: we use build_column_default, and not just the cooked default
     * returned by AddRelationNewConstraints, so that the right thing happens
     * when a datatype's default applies.
     *
     * We skip this step completely for views and foreign tables.  For a view,
     * we can only get here from CREATE OR REPLACE VIEW, which historically
     * doesn't set up defaults, not even for domain-typed columns.  And in any
     * case we mustn't invoke Phase 3 on a view or foreign table, since they
     * have no storage.
     */
    if (relkind != RELKIND_VIEW && relkind != RELKIND_COMPOSITE_TYPE
        && relkind != RELKIND_FOREIGN_TABLE && attribute.attnum > 0)
    {
        defval = (Expr *) build_column_default(rel, attribute.attnum);

        if (!defval && GetDomainConstraints(typeOid) != NIL)
        {
            Oid         baseTypeId;
            int32       baseTypeMod;
            Oid         baseTypeColl;

            baseTypeMod = typmod;
            baseTypeId = getBaseTypeAndTypmod(typeOid, &baseTypeMod);
            baseTypeColl = get_typcollation(baseTypeId);
            defval = (Expr *) makeNullConst(baseTypeId, baseTypeMod, baseTypeColl);
            defval = (Expr *) coerce_to_target_type(NULL,
                                                    (Node *) defval,
                                                    baseTypeId,
                                                    typeOid,
                                                    typmod,
                                                    COERCION_ASSIGNMENT,
                                                    COERCE_IMPLICIT_CAST,
                                                    -1);
            if (defval == NULL) /* should not happen */
                elog(ERROR, "failed to coerce base type to domain");
        }

        if (defval)
        {
            NewColumnValue *newval;

            newval = (NewColumnValue *) palloc0(sizeof(NewColumnValue));
            newval->attnum = attribute.attnum;
            newval->expr = expression_planner(defval);

            tab->newvals = lappend(tab->newvals, newval);
            tab->rewrite = true;
        }

        /*
         * If the new column is NOT NULL, tell Phase 3 it needs to test that.
         * (Note we don't do this for an OID column.  OID will be marked not
         * null, but since it's filled specially, there's no need to test
         * anything.)
         */
        tab->new_notnull |= colDef->is_not_null;
    }

    /*
     * If we are adding an OID column, we have to tell Phase 3 to rewrite the
     * table to fix that.
     */
    if (isOid)
        tab->rewrite = true;

    /*
     * Add needed dependency entries for the new column.
     */
    add_column_datatype_dependency(myrelid, newattnum, attribute.atttypid);
    add_column_collation_dependency(myrelid, newattnum, attribute.attcollation);

    /*
     * Propagate to children as appropriate.  Unlike most other ALTER
     * routines, we have to do this one level of recursion at a time; we can't
     * use find_all_inheritors to do it in one pass.
     */
    children = find_inheritance_children(RelationGetRelid(rel), lockmode);

    /*
     * If we are told not to recurse, there had better not be any child
     * tables; else the addition would put them out of step.
     */
    if (children && !recurse)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                 errmsg("column must be added to child tables too")));

    /* Children should see column as singly inherited */
    if (!recursing)
    {
        colDef = copyObject(colDef);
        colDef->inhcount = 1;
        colDef->is_local = false;
    }

    foreach(child, children)
    {
        Oid         childrelid = lfirst_oid(child);
        Relation    childrel;
        AlteredTableInfo *childtab;

        /* find_inheritance_children already got lock */
        childrel = heap_open(childrelid, NoLock);
        CheckTableNotInUse(childrel, "ALTER TABLE");

        /* Find or create work queue entry for this table */
        childtab = ATGetQueueEntry(wqueue, childrel);

        /* Recurse to child */
        ATExecAddColumn(wqueue, childtab, childrel,
                        colDef, isOid, recurse, true, lockmode);

        heap_close(childrel, NoLock);
    }
}

/*
 * If a new or renamed column will collide with the name of an existing
 * column, error out.
 */
static void
check_for_column_name_collision(Relation rel, const char *colname)
{
    HeapTuple   attTuple;
    int         attnum;

    /*
     * this test is deliberately not attisdropped-aware, since if one tries to
     * add a column matching a dropped column name, it's gonna fail anyway.
     */
    attTuple = SearchSysCache2(ATTNAME,
                               ObjectIdGetDatum(RelationGetRelid(rel)),
                               PointerGetDatum(colname));
    if (!HeapTupleIsValid(attTuple))
        return;

    attnum = ((Form_pg_attribute) GETSTRUCT(attTuple))->attnum;
    ReleaseSysCache(attTuple);

    /*
     * We throw a different error message for conflicts with system column
     * names, since they are normally not shown and the user might otherwise
     * be confused about the reason for the conflict.
     */
    if (attnum <= 0)
        ereport(ERROR,
                (errcode(ERRCODE_DUPLICATE_COLUMN),
             errmsg("column name \"%s\" conflicts with a system column name",
                    colname)));
    else
        ereport(ERROR,
                (errcode(ERRCODE_DUPLICATE_COLUMN),
                 errmsg("column \"%s\" of relation \"%s\" already exists",
                        colname, RelationGetRelationName(rel))));
}

/*
 * Install a column's dependency on its datatype.
 */
static void
add_column_datatype_dependency(Oid relid, int32 attnum, Oid typid)
{
    ObjectAddress myself,
                referenced;

    myself.classId = RelationRelationId;
    myself.objectId = relid;
    myself.objectSubId = attnum;
    referenced.classId = TypeRelationId;
    referenced.objectId = typid;
    referenced.objectSubId = 0;
    recordDependencyOn(&myself, &referenced, DEPENDENCY_NORMAL);
}

/*
 * Install a column's dependency on its collation.
 */
static void
add_column_collation_dependency(Oid relid, int32 attnum, Oid collid)
{
    ObjectAddress myself,
                referenced;

    /* We know the default collation is pinned, so don't bother recording it */
    if (OidIsValid(collid) && collid != DEFAULT_COLLATION_OID)
    {
        myself.classId = RelationRelationId;
        myself.objectId = relid;
        myself.objectSubId = attnum;
        referenced.classId = CollationRelationId;
        referenced.objectId = collid;
        referenced.objectSubId = 0;
        recordDependencyOn(&myself, &referenced, DEPENDENCY_NORMAL);
    }
}

/*
 * ALTER TABLE SET WITH OIDS
 *
 * Basically this is an ADD COLUMN for the special OID column.  We have
 * to cons up a ColumnDef node because the ADD COLUMN code needs one.
 */
static void
ATPrepAddOids(List **wqueue, Relation rel, bool recurse, AlterTableCmd *cmd, LOCKMODE lockmode)
{
    /* If we're recursing to a child table, the ColumnDef is already set up */
    if (cmd->def == NULL)
    {
        ColumnDef  *cdef = makeNode(ColumnDef);

        cdef->colname = pstrdup("oid");
        cdef->typeName = makeTypeNameFromOid(OIDOID, -1);
        cdef->inhcount = 0;
        cdef->is_local = true;
        cdef->is_not_null = true;
        cdef->storage = 0;
        cmd->def = (Node *) cdef;
    }
    ATPrepAddColumn(wqueue, rel, recurse, false, cmd, lockmode);

    if (recurse)
        cmd->subtype = AT_AddOidsRecurse;
}

/*
 * ALTER TABLE ALTER COLUMN DROP NOT NULL
 */
static void
ATExecDropNotNull(Relation rel, const char *colName, LOCKMODE lockmode)
{
    HeapTuple   tuple;
    AttrNumber  attnum;
    Relation    attr_rel;
    List       *indexoidlist;
    ListCell   *indexoidscan;

    /*
     * lookup the attribute
     */
    attr_rel = heap_open(AttributeRelationId, RowExclusiveLock);

    tuple = SearchSysCacheCopyAttName(RelationGetRelid(rel), colName);

    if (!HeapTupleIsValid(tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_COLUMN),
                 errmsg("column \"%s\" of relation \"%s\" does not exist",
                        colName, RelationGetRelationName(rel))));

    attnum = ((Form_pg_attribute) GETSTRUCT(tuple))->attnum;

    /* Prevent them from altering a system attribute */
    if (attnum <= 0)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot alter system column \"%s\"",
                        colName)));

    /*
     * Check that the attribute is not in a primary key
     *
     * Note: we'll throw error even if the pkey index is not valid.
     */

    /* Loop over all indexes on the relation */
    indexoidlist = RelationGetIndexList(rel);

    foreach(indexoidscan, indexoidlist)
    {
        Oid         indexoid = lfirst_oid(indexoidscan);
        HeapTuple   indexTuple;
        Form_pg_index indexStruct;
        int         i;

        indexTuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(indexoid));
        if (!HeapTupleIsValid(indexTuple))
            elog(ERROR, "cache lookup failed for index %u", indexoid);
        indexStruct = (Form_pg_index) GETSTRUCT(indexTuple);

        /* If the index is not a primary key, skip the check */
        if (indexStruct->indisprimary)
        {
            /*
             * Loop over each attribute in the primary key and see if it
             * matches the to-be-altered attribute
             */
            for (i = 0; i < indexStruct->indnatts; i++)
            {
                if (indexStruct->indkey.values[i] == attnum)
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                             errmsg("column \"%s\" is in a primary key",
                                    colName)));
            }
        }

        ReleaseSysCache(indexTuple);
    }

    list_free(indexoidlist);

    /*
     * Okay, actually perform the catalog change ... if needed
     */
    if (((Form_pg_attribute) GETSTRUCT(tuple))->attnotnull)
    {
        ((Form_pg_attribute) GETSTRUCT(tuple))->attnotnull = FALSE;

        simple_heap_update(attr_rel, &tuple->t_self, tuple);

        /* keep the system catalog indexes current */
        CatalogUpdateIndexes(attr_rel, tuple);
    }

    InvokeObjectPostAlterHook(RelationRelationId,
                              RelationGetRelid(rel), attnum);

    heap_close(attr_rel, RowExclusiveLock);
}

/*
 * ALTER TABLE ALTER COLUMN SET NOT NULL
 */
static void
ATExecSetNotNull(AlteredTableInfo *tab, Relation rel,
                 const char *colName, LOCKMODE lockmode)
{
    HeapTuple   tuple;
    AttrNumber  attnum;
    Relation    attr_rel;

    /*
     * lookup the attribute
     */
    attr_rel = heap_open(AttributeRelationId, RowExclusiveLock);

    tuple = SearchSysCacheCopyAttName(RelationGetRelid(rel), colName);

    if (!HeapTupleIsValid(tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_COLUMN),
                 errmsg("column \"%s\" of relation \"%s\" does not exist",
                        colName, RelationGetRelationName(rel))));

    attnum = ((Form_pg_attribute) GETSTRUCT(tuple))->attnum;

    /* Prevent them from altering a system attribute */
    if (attnum <= 0)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot alter system column \"%s\"",
                        colName)));

    /*
     * Okay, actually perform the catalog change ... if needed
     */
    if (!((Form_pg_attribute) GETSTRUCT(tuple))->attnotnull)
    {
        ((Form_pg_attribute) GETSTRUCT(tuple))->attnotnull = TRUE;

        simple_heap_update(attr_rel, &tuple->t_self, tuple);

        /* keep the system catalog indexes current */
        CatalogUpdateIndexes(attr_rel, tuple);

        /* Tell Phase 3 it needs to test the constraint */
        tab->new_notnull = true;
    }

    InvokeObjectPostAlterHook(RelationRelationId,
                              RelationGetRelid(rel), attnum);

    heap_close(attr_rel, RowExclusiveLock);
}

/*
 * ALTER TABLE ALTER COLUMN SET/DROP DEFAULT
 */
static void
ATExecColumnDefault(Relation rel, const char *colName,
                    Node *newDefault, LOCKMODE lockmode)
{
    AttrNumber  attnum;

    /*
     * get the number of the attribute
     */
    attnum = get_attnum(RelationGetRelid(rel), colName);
    if (attnum == InvalidAttrNumber)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_COLUMN),
                 errmsg("column \"%s\" of relation \"%s\" does not exist",
                        colName, RelationGetRelationName(rel))));

    /* Prevent them from altering a system attribute */
    if (attnum <= 0)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot alter system column \"%s\"",
                        colName)));

    /*
     * Remove any old default for the column.  We use RESTRICT here for
     * safety, but at present we do not expect anything to depend on the
     * default.
     *
     * We treat removing the existing default as an internal operation when it
     * is preparatory to adding a new default, but as a user-initiated
     * operation when the user asked for a drop.
     */
    RemoveAttrDefault(RelationGetRelid(rel), attnum, DROP_RESTRICT, false,
                      newDefault == NULL ? false : true);

    if (newDefault)
    {
        /* SET DEFAULT */
        RawColumnDefault *rawEnt;

        rawEnt = (RawColumnDefault *) palloc(sizeof(RawColumnDefault));
        rawEnt->attnum = attnum;
        rawEnt->raw_default = newDefault;

        /*
         * This function is intended for CREATE TABLE, so it processes a
         * _list_ of defaults, but we just do one.
         */
        AddRelationNewConstraints(rel, list_make1(rawEnt), NIL,
                                  false, true, false);
    }
}

/*
 * ALTER TABLE ALTER COLUMN SET STATISTICS
 */
static void
ATPrepSetStatistics(Relation rel, const char *colName, Node *newValue, LOCKMODE lockmode)
{
    /*
     * We do our own permission checking because (a) we want to allow SET
     * STATISTICS on indexes (for expressional index columns), and (b) we want
     * to allow SET STATISTICS on system catalogs without requiring
     * allowSystemTableMods to be turned on.
     */
    if (rel->rd_rel->relkind != RELKIND_RELATION &&
        rel->rd_rel->relkind != RELKIND_MATVIEW &&
        rel->rd_rel->relkind != RELKIND_INDEX &&
        rel->rd_rel->relkind != RELKIND_FOREIGN_TABLE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not a table, materialized view, index, or foreign table",
                        RelationGetRelationName(rel))));

    /* Permissions checks */
    if (!pg_class_ownercheck(RelationGetRelid(rel), GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
                       RelationGetRelationName(rel));
}

static void
ATExecSetStatistics(Relation rel, const char *colName, Node *newValue, LOCKMODE lockmode)
{
    int         newtarget;
    Relation    attrelation;
    HeapTuple   tuple;
    Form_pg_attribute attrtuple;

    Assert(IsA(newValue, Integer));
    newtarget = intVal(newValue);

    /*
     * Limit target to a sane range
     */
    if (newtarget < -1)
    {
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("statistics target %d is too low",
                        newtarget)));
    }
    else if (newtarget > 10000)
    {
        newtarget = 10000;
        ereport(WARNING,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("lowering statistics target to %d",
                        newtarget)));
    }

    attrelation = heap_open(AttributeRelationId, RowExclusiveLock);

    tuple = SearchSysCacheCopyAttName(RelationGetRelid(rel), colName);

    if (!HeapTupleIsValid(tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_COLUMN),
                 errmsg("column \"%s\" of relation \"%s\" does not exist",
                        colName, RelationGetRelationName(rel))));
    attrtuple = (Form_pg_attribute) GETSTRUCT(tuple);

    if (attrtuple->attnum <= 0)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot alter system column \"%s\"",
                        colName)));

    attrtuple->attstattarget = newtarget;

    simple_heap_update(attrelation, &tuple->t_self, tuple);

    /* keep system catalog indexes current */
    CatalogUpdateIndexes(attrelation, tuple);

    InvokeObjectPostAlterHook(RelationRelationId,
                              RelationGetRelid(rel),
                              attrtuple->attnum);
    heap_freetuple(tuple);

    heap_close(attrelation, RowExclusiveLock);
}

static void
ATExecSetOptions(Relation rel, const char *colName, Node *options,
                 bool isReset, LOCKMODE lockmode)
{
    Relation    attrelation;
    HeapTuple   tuple,
                newtuple;
    Form_pg_attribute attrtuple;
    Datum       datum,
                newOptions;
    bool        isnull;
    Datum       repl_val[Natts_pg_attribute];
    bool        repl_null[Natts_pg_attribute];
    bool        repl_repl[Natts_pg_attribute];

    attrelation = heap_open(AttributeRelationId, RowExclusiveLock);

    tuple = SearchSysCacheAttName(RelationGetRelid(rel), colName);

    if (!HeapTupleIsValid(tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_COLUMN),
                 errmsg("column \"%s\" of relation \"%s\" does not exist",
                        colName, RelationGetRelationName(rel))));
    attrtuple = (Form_pg_attribute) GETSTRUCT(tuple);

    if (attrtuple->attnum <= 0)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot alter system column \"%s\"",
                        colName)));

    /* Generate new proposed attoptions (text array) */
    Assert(IsA(options, List));
    datum = SysCacheGetAttr(ATTNAME, tuple, Anum_pg_attribute_attoptions,
                            &isnull);
    newOptions = transformRelOptions(isnull ? (Datum) 0 : datum,
                                     (List *) options, NULL, NULL, false,
                                     isReset);
    /* Validate new options */
    (void) attribute_reloptions(newOptions, true);

    /* Build new tuple. */
    memset(repl_null, false, sizeof(repl_null));
    memset(repl_repl, false, sizeof(repl_repl));
    if (newOptions != (Datum) 0)
        repl_val[Anum_pg_attribute_attoptions - 1] = newOptions;
    else
        repl_null[Anum_pg_attribute_attoptions - 1] = true;
    repl_repl[Anum_pg_attribute_attoptions - 1] = true;
    newtuple = heap_modify_tuple(tuple, RelationGetDescr(attrelation),
                                 repl_val, repl_null, repl_repl);

    /* Update system catalog. */
    simple_heap_update(attrelation, &newtuple->t_self, newtuple);
    CatalogUpdateIndexes(attrelation, newtuple);

    InvokeObjectPostAlterHook(RelationRelationId,
                              RelationGetRelid(rel),
                              attrtuple->attnum);
    heap_freetuple(newtuple);

    ReleaseSysCache(tuple);

    heap_close(attrelation, RowExclusiveLock);
}

/*
 * ALTER TABLE ALTER COLUMN SET STORAGE
 */
static void
ATExecSetStorage(Relation rel, const char *colName, Node *newValue, LOCKMODE lockmode)
{
    char       *storagemode;
    char        newstorage;
    Relation    attrelation;
    HeapTuple   tuple;
    Form_pg_attribute attrtuple;

    Assert(IsA(newValue, String));
    storagemode = strVal(newValue);

    if (pg_strcasecmp(storagemode, "plain") == 0)
        newstorage = 'p';
    else if (pg_strcasecmp(storagemode, "external") == 0)
        newstorage = 'e';
    else if (pg_strcasecmp(storagemode, "extended") == 0)
        newstorage = 'x';
    else if (pg_strcasecmp(storagemode, "main") == 0)
        newstorage = 'm';
    else
    {
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("invalid storage type \"%s\"",
                        storagemode)));
        newstorage = 0;         /* keep compiler quiet */
    }

    attrelation = heap_open(AttributeRelationId, RowExclusiveLock);

    tuple = SearchSysCacheCopyAttName(RelationGetRelid(rel), colName);

    if (!HeapTupleIsValid(tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_COLUMN),
                 errmsg("column \"%s\" of relation \"%s\" does not exist",
                        colName, RelationGetRelationName(rel))));
    attrtuple = (Form_pg_attribute) GETSTRUCT(tuple);

    if (attrtuple->attnum <= 0)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot alter system column \"%s\"",
                        colName)));

    /*
     * safety check: do not allow toasted storage modes unless column datatype
     * is TOAST-aware.
     */
    if (newstorage == 'p' || TypeIsToastable(attrtuple->atttypid))
        attrtuple->attstorage = newstorage;
    else
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("column data type %s can only have storage PLAIN",
                        format_type_be(attrtuple->atttypid))));

    simple_heap_update(attrelation, &tuple->t_self, tuple);

    /* keep system catalog indexes current */
    CatalogUpdateIndexes(attrelation, tuple);

    InvokeObjectPostAlterHook(RelationRelationId,
                              RelationGetRelid(rel),
                              attrtuple->attnum);

    heap_freetuple(tuple);

    heap_close(attrelation, RowExclusiveLock);
}


/*
 * ALTER TABLE DROP COLUMN
 *
 * DROP COLUMN cannot use the normal ALTER TABLE recursion mechanism,
 * because we have to decide at runtime whether to recurse or not depending
 * on whether attinhcount goes to zero or not.  (We can't check this in a
 * static pre-pass because it won't handle multiple inheritance situations
 * correctly.)
 */
static void
ATPrepDropColumn(List **wqueue, Relation rel, bool recurse, bool recursing,
                 AlterTableCmd *cmd, LOCKMODE lockmode)
{
    if (rel->rd_rel->reloftype && !recursing)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("cannot drop column from typed table")));

    if (rel->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
        ATTypedTableRecursion(wqueue, rel, cmd, lockmode);

    if (recurse)
        cmd->subtype = AT_DropColumnRecurse;
}

static void
ATExecDropColumn(List **wqueue, Relation rel, const char *colName,
                 DropBehavior behavior,
                 bool recurse, bool recursing,
                 bool missing_ok, LOCKMODE lockmode)
{
    HeapTuple   tuple;
    Form_pg_attribute targetatt;
    AttrNumber  attnum;
    List       *children;
    ObjectAddress object;

    /* At top level, permission check was done in ATPrepCmd, else do it */
    if (recursing)
        ATSimplePermissions(rel, ATT_TABLE);

    /*
     * get the number of the attribute
     */
    tuple = SearchSysCacheAttName(RelationGetRelid(rel), colName);
    if (!HeapTupleIsValid(tuple))
    {
        if (!missing_ok)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_COLUMN),
                     errmsg("column \"%s\" of relation \"%s\" does not exist",
                            colName, RelationGetRelationName(rel))));
        }
        else
        {
            ereport(NOTICE,
                    (errmsg("column \"%s\" of relation \"%s\" does not exist, skipping",
                            colName, RelationGetRelationName(rel))));
            return;
        }
    }
    targetatt = (Form_pg_attribute) GETSTRUCT(tuple);

    attnum = targetatt->attnum;

    /* Can't drop a system attribute, except OID */
    if (attnum <= 0 && attnum != ObjectIdAttributeNumber)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot drop system column \"%s\"",
                        colName)));

    /* Don't drop inherited columns */
    if (targetatt->attinhcount > 0 && !recursing)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                 errmsg("cannot drop inherited column \"%s\"",
                        colName)));

    ReleaseSysCache(tuple);

    /*
     * Propagate to children as appropriate.  Unlike most other ALTER
     * routines, we have to do this one level of recursion at a time; we can't
     * use find_all_inheritors to do it in one pass.
     */
    children = find_inheritance_children(RelationGetRelid(rel), lockmode);

    if (children)
    {
        Relation    attr_rel;
        ListCell   *child;

        attr_rel = heap_open(AttributeRelationId, RowExclusiveLock);
        foreach(child, children)
        {
            Oid         childrelid = lfirst_oid(child);
            Relation    childrel;
            Form_pg_attribute childatt;

            /* find_inheritance_children already got lock */
            childrel = heap_open(childrelid, NoLock);
            CheckTableNotInUse(childrel, "ALTER TABLE");

            tuple = SearchSysCacheCopyAttName(childrelid, colName);
            if (!HeapTupleIsValid(tuple))       /* shouldn't happen */
                elog(ERROR, "cache lookup failed for attribute \"%s\" of relation %u",
                     colName, childrelid);
            childatt = (Form_pg_attribute) GETSTRUCT(tuple);

            if (childatt->attinhcount <= 0)     /* shouldn't happen */
                elog(ERROR, "relation %u has non-inherited attribute \"%s\"",
                     childrelid, colName);

            if (recurse)
            {
                /*
                 * If the child column has other definition sources, just
                 * decrement its inheritance count; if not, recurse to delete
                 * it.
                 */
                if (childatt->attinhcount == 1 && !childatt->attislocal)
                {
                    /* Time to delete this child column, too */
                    ATExecDropColumn(wqueue, childrel, colName,
                                     behavior, true, true,
                                     false, lockmode);
                }
                else
                {
                    /* Child column must survive my deletion */
                    childatt->attinhcount--;

                    simple_heap_update(attr_rel, &tuple->t_self, tuple);

                    /* keep the system catalog indexes current */
                    CatalogUpdateIndexes(attr_rel, tuple);

                    /* Make update visible */
                    CommandCounterIncrement();
                }
            }
            else
            {
                /*
                 * If we were told to drop ONLY in this table (no recursion),
                 * we need to mark the inheritors' attributes as locally
                 * defined rather than inherited.
                 */
                childatt->attinhcount--;
                childatt->attislocal = true;

                simple_heap_update(attr_rel, &tuple->t_self, tuple);

                /* keep the system catalog indexes current */
                CatalogUpdateIndexes(attr_rel, tuple);

                /* Make update visible */
                CommandCounterIncrement();
            }

            heap_freetuple(tuple);

            heap_close(childrel, NoLock);
        }
        heap_close(attr_rel, RowExclusiveLock);
    }

    /*
     * Perform the actual column deletion
     */
    object.classId = RelationRelationId;
    object.objectId = RelationGetRelid(rel);
    object.objectSubId = attnum;

    performDeletion(&object, behavior, 0);

    /*
     * If we dropped the OID column, must adjust pg_class.relhasoids and tell
     * Phase 3 to physically get rid of the column.  We formerly left the
     * column in place physically, but this caused subtle problems.  See
     * http://archives.postgresql.org/pgsql-hackers/2009-02/msg00363.php
     */
    if (attnum == ObjectIdAttributeNumber)
    {
        Relation    class_rel;
        Form_pg_class tuple_class;
        AlteredTableInfo *tab;

        class_rel = heap_open(RelationRelationId, RowExclusiveLock);

        tuple = SearchSysCacheCopy1(RELOID,
                                    ObjectIdGetDatum(RelationGetRelid(rel)));
        if (!HeapTupleIsValid(tuple))
            elog(ERROR, "cache lookup failed for relation %u",
                 RelationGetRelid(rel));
        tuple_class = (Form_pg_class) GETSTRUCT(tuple);

        tuple_class->relhasoids = false;
        simple_heap_update(class_rel, &tuple->t_self, tuple);

        /* Keep the catalog indexes up to date */
        CatalogUpdateIndexes(class_rel, tuple);

        heap_close(class_rel, RowExclusiveLock);

        /* Find or create work queue entry for this table */
        tab = ATGetQueueEntry(wqueue, rel);

        /* Tell Phase 3 to physically remove the OID column */
        tab->rewrite = true;
    }
}

/*
 * ALTER TABLE ADD INDEX
 *
 * There is no such command in the grammar, but parse_utilcmd.c converts
 * UNIQUE and PRIMARY KEY constraints into AT_AddIndex subcommands.  This lets
 * us schedule creation of the index at the appropriate time during ALTER.
 */
static void
ATExecAddIndex(AlteredTableInfo *tab, Relation rel,
               IndexStmt *stmt, bool is_rebuild, LOCKMODE lockmode)
{
    bool        check_rights;
    bool        skip_build;
    bool        quiet;
    Oid         new_index;

    Assert(IsA(stmt, IndexStmt));
    Assert(!stmt->concurrent);

    /* suppress schema rights check when rebuilding existing index */
    check_rights = !is_rebuild;
    /* skip index build if phase 3 will do it or we're reusing an old one */
    skip_build = tab->rewrite || OidIsValid(stmt->oldNode);
    /* suppress notices when rebuilding existing index */
    quiet = is_rebuild;

    /* The IndexStmt has already been through transformIndexStmt */

    new_index = DefineIndex(stmt,
                            InvalidOid, /* no predefined OID */
                            true,       /* is_alter_table */
                            check_rights,
                            skip_build,
                            quiet);

    /*
     * If TryReuseIndex() stashed a relfilenode for us, we used it for the new
     * index instead of building from scratch.  The DROP of the old edition of
     * this index will have scheduled the storage for deletion at commit, so
     * cancel that pending deletion.
     */
    if (OidIsValid(stmt->oldNode))
    {
        Relation    irel = index_open(new_index, NoLock);

        RelationPreserveStorage(irel->rd_node, true);
        index_close(irel, NoLock);
    }
}

/*
 * ALTER TABLE ADD CONSTRAINT USING INDEX
 */
static void
ATExecAddIndexConstraint(AlteredTableInfo *tab, Relation rel,
                         IndexStmt *stmt, LOCKMODE lockmode)
{
    Oid         index_oid = stmt->indexOid;
    Relation    indexRel;
    char       *indexName;
    IndexInfo  *indexInfo;
    char       *constraintName;
    char        constraintType;

    Assert(IsA(stmt, IndexStmt));
    Assert(OidIsValid(index_oid));
    Assert(stmt->isconstraint);

    indexRel = index_open(index_oid, AccessShareLock);

    indexName = pstrdup(RelationGetRelationName(indexRel));

    indexInfo = BuildIndexInfo(indexRel);

    /* this should have been checked at parse time */
    if (!indexInfo->ii_Unique)
        elog(ERROR, "index \"%s\" is not unique", indexName);

    /*
     * Determine name to assign to constraint.  We require a constraint to
     * have the same name as the underlying index; therefore, use the index's
     * existing name as the default constraint name, and if the user
     * explicitly gives some other name for the constraint, rename the index
     * to match.
     */
    constraintName = stmt->idxname;
    if (constraintName == NULL)
        constraintName = indexName;
    else if (strcmp(constraintName, indexName) != 0)
    {
        ereport(NOTICE,
                (errmsg("ALTER TABLE / ADD CONSTRAINT USING INDEX will rename index \"%s\" to \"%s\"",
                        indexName, constraintName)));
        RenameRelationInternal(index_oid, constraintName, false);
    }

    /* Extra checks needed if making primary key */
    if (stmt->primary)
        index_check_primary_key(rel, indexInfo, true);

    /* Note we currently don't support EXCLUSION constraints here */
    if (stmt->primary)
        constraintType = CONSTRAINT_PRIMARY;
    else
        constraintType = CONSTRAINT_UNIQUE;

    /* Create the catalog entries for the constraint */
    index_constraint_create(rel,
                            index_oid,
                            indexInfo,
                            constraintName,
                            constraintType,
                            stmt->deferrable,
                            stmt->initdeferred,
                            stmt->primary,
                            true, /* update pg_index */
                            true, /* remove old dependencies */
                            allowSystemTableMods,
                            false); /* is_internal */

    index_close(indexRel, NoLock);
}

/*
 * ALTER TABLE ADD CONSTRAINT
 */
static void
ATExecAddConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
                    Constraint *newConstraint, bool recurse, bool is_readd,
                    LOCKMODE lockmode)
{
    Assert(IsA(newConstraint, Constraint));

    /*
     * Currently, we only expect to see CONSTR_CHECK and CONSTR_FOREIGN nodes
     * arriving here (see the preprocessing done in parse_utilcmd.c).  Use a
     * switch anyway to make it easier to add more code later.
     */
    switch (newConstraint->contype)
    {
        case CONSTR_CHECK:
            ATAddCheckConstraint(wqueue, tab, rel,
                                 newConstraint, recurse, false, is_readd,
                                 lockmode);
            break;

        case CONSTR_FOREIGN:

            /*
             * Note that we currently never recurse for FK constraints, so the
             * "recurse" flag is silently ignored.
             *
             * Assign or validate constraint name
             */
            if (newConstraint->conname)
            {
                if (ConstraintNameIsUsed(CONSTRAINT_RELATION,
                                         RelationGetRelid(rel),
                                         RelationGetNamespace(rel),
                                         newConstraint->conname))
                    ereport(ERROR,
                            (errcode(ERRCODE_DUPLICATE_OBJECT),
                             errmsg("constraint \"%s\" for relation \"%s\" already exists",
                                    newConstraint->conname,
                                    RelationGetRelationName(rel))));
            }
            else
                newConstraint->conname =
                    ChooseConstraintName(RelationGetRelationName(rel),
                                   strVal(linitial(newConstraint->fk_attrs)),
                                         "fkey",
                                         RelationGetNamespace(rel),
                                         NIL);

            ATAddForeignKeyConstraint(tab, rel, newConstraint, lockmode);
            break;

        default:
            elog(ERROR, "unrecognized constraint type: %d",
                 (int) newConstraint->contype);
    }
}

/*
 * Add a check constraint to a single table and its children
 *
 * Subroutine for ATExecAddConstraint.
 *
 * We must recurse to child tables during execution, rather than using
 * ALTER TABLE's normal prep-time recursion.  The reason is that all the
 * constraints *must* be given the same name, else they won't be seen as
 * related later.  If the user didn't explicitly specify a name, then
 * AddRelationNewConstraints would normally assign different names to the
 * child constraints.  To fix that, we must capture the name assigned at
 * the parent table and pass that down.
 *
 * When re-adding a previously existing constraint (during ALTER COLUMN TYPE),
 * we don't need to recurse here, because recursion will be carried out at a
 * higher level; the constraint name issue doesn't apply because the names
 * have already been assigned and are just being re-used.  We need a separate
 * "is_readd" flag for that; just setting recurse=false would result in an
 * error if there are child tables.
 */
static void
ATAddCheckConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
                     Constraint *constr, bool recurse, bool recursing,
                     bool is_readd, LOCKMODE lockmode)
{
    List       *newcons;
    ListCell   *lcon;
    List       *children;
    ListCell   *child;

    /* At top level, permission check was done in ATPrepCmd, else do it */
    if (recursing)
        ATSimplePermissions(rel, ATT_TABLE);

    /*
     * Call AddRelationNewConstraints to do the work, making sure it works on
     * a copy of the Constraint so transformExpr can't modify the original. It
     * returns a list of cooked constraints.
     *
     * If the constraint ends up getting merged with a pre-existing one, it's
     * omitted from the returned list, which is what we want: we do not need
     * to do any validation work.  That can only happen at child tables,
     * though, since we disallow merging at the top level.
     */
    newcons = AddRelationNewConstraints(rel, NIL,
                                        list_make1(copyObject(constr)),
                                        recursing,      /* allow_merge */
                                        !recursing,     /* is_local */
                                        is_readd);      /* is_internal */

    /* Add each to-be-validated constraint to Phase 3's queue */
    foreach(lcon, newcons)
    {
        CookedConstraint *ccon = (CookedConstraint *) lfirst(lcon);

        if (!ccon->skip_validation)
        {
            NewConstraint *newcon;

            newcon = (NewConstraint *) palloc0(sizeof(NewConstraint));
            newcon->name = ccon->name;
            newcon->contype = ccon->contype;
            /* ExecQual wants implicit-AND format */
            newcon->qual = (Node *) make_ands_implicit((Expr *) ccon->expr);

            tab->constraints = lappend(tab->constraints, newcon);
        }

        /* Save the actually assigned name if it was defaulted */
        if (constr->conname == NULL)
            constr->conname = ccon->name;
    }

    /* At this point we must have a locked-down name to use */
    Assert(constr->conname != NULL);

    /* Advance command counter in case same table is visited multiple times */
    CommandCounterIncrement();

    /*
     * If the constraint got merged with an existing constraint, we're done.
     * We mustn't recurse to child tables in this case, because they've
     * already got the constraint, and visiting them again would lead to an
     * incorrect value for coninhcount.
     */
    if (newcons == NIL)
        return;

    /*
     * If adding a NO INHERIT constraint, no need to find our children.
     * Likewise, in a re-add operation, we don't need to recurse (that will be
     * handled at higher levels).
     */
    if (constr->is_no_inherit || is_readd)
        return;

    /*
     * Propagate to children as appropriate.  Unlike most other ALTER
     * routines, we have to do this one level of recursion at a time; we can't
     * use find_all_inheritors to do it in one pass.
     */
    children = find_inheritance_children(RelationGetRelid(rel), lockmode);

    /*
     * Check if ONLY was specified with ALTER TABLE.  If so, allow the
     * contraint creation only if there are no children currently.  Error out
     * otherwise.
     */
    if (!recurse && children != NIL)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                 errmsg("constraint must be added to child tables too")));

    foreach(child, children)
    {
        Oid         childrelid = lfirst_oid(child);
        Relation    childrel;
        AlteredTableInfo *childtab;

        /* find_inheritance_children already got lock */
        childrel = heap_open(childrelid, NoLock);
        CheckTableNotInUse(childrel, "ALTER TABLE");

        /* Find or create work queue entry for this table */
        childtab = ATGetQueueEntry(wqueue, childrel);

        /* Recurse to child */
        ATAddCheckConstraint(wqueue, childtab, childrel,
                             constr, recurse, true, is_readd, lockmode);

        heap_close(childrel, NoLock);
    }
}

/*
 * Add a foreign-key constraint to a single table
 *
 * Subroutine for ATExecAddConstraint.  Must already hold exclusive
 * lock on the rel, and have done appropriate validity checks for it.
 * We do permissions checks here, however.
 */
static void
ATAddForeignKeyConstraint(AlteredTableInfo *tab, Relation rel,
                          Constraint *fkconstraint, LOCKMODE lockmode)
{
    Relation    pkrel;
    int16       pkattnum[INDEX_MAX_KEYS];
    int16       fkattnum[INDEX_MAX_KEYS];
    Oid         pktypoid[INDEX_MAX_KEYS];
    Oid         fktypoid[INDEX_MAX_KEYS];
    Oid         opclasses[INDEX_MAX_KEYS];
    Oid         pfeqoperators[INDEX_MAX_KEYS];
    Oid         ppeqoperators[INDEX_MAX_KEYS];
    Oid         ffeqoperators[INDEX_MAX_KEYS];
    int         i;
    int         numfks,
                numpks;
    Oid         indexOid;
    Oid         constrOid;
    bool        old_check_ok;
    ListCell   *old_pfeqop_item = list_head(fkconstraint->old_conpfeqop);

    /*
     * Grab an exclusive lock on the pk table, so that someone doesn't delete
     * rows out from under us. (Although a lesser lock would do for that
     * purpose, we'll need exclusive lock anyway to add triggers to the pk
     * table; trying to start with a lesser lock will just create a risk of
     * deadlock.)
     */
    pkrel = heap_openrv(fkconstraint->pktable, AccessExclusiveLock);

    /*
     * Validity checks (permission checks wait till we have the column
     * numbers)
     */
    if (pkrel->rd_rel->relkind != RELKIND_RELATION)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("referenced relation \"%s\" is not a table",
                        RelationGetRelationName(pkrel))));

    if (!allowSystemTableMods && IsSystemRelation(pkrel))
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied: \"%s\" is a system catalog",
                        RelationGetRelationName(pkrel))));

    /*
     * References from permanent or unlogged tables to temp tables, and from
     * permanent tables to unlogged tables, are disallowed because the
     * referenced data can vanish out from under us.  References from temp
     * tables to any other table type are also disallowed, because other
     * backends might need to run the RI triggers on the perm table, but they
     * can't reliably see tuples in the local buffers of other backends.
     */
    switch (rel->rd_rel->relpersistence)
    {
        case RELPERSISTENCE_PERMANENT:
            if (pkrel->rd_rel->relpersistence != RELPERSISTENCE_PERMANENT)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                         errmsg("constraints on permanent tables may reference only permanent tables")));
            break;
        case RELPERSISTENCE_UNLOGGED:
            if (pkrel->rd_rel->relpersistence != RELPERSISTENCE_PERMANENT
                && pkrel->rd_rel->relpersistence != RELPERSISTENCE_UNLOGGED)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                         errmsg("constraints on unlogged tables may reference only permanent or unlogged tables")));
            break;
        case RELPERSISTENCE_TEMP:
            if (pkrel->rd_rel->relpersistence != RELPERSISTENCE_TEMP)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                         errmsg("constraints on temporary tables may reference only temporary tables")));
            if (!pkrel->rd_islocaltemp || !rel->rd_islocaltemp)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                         errmsg("constraints on temporary tables must involve temporary tables of this session")));
            break;
    }

    /*
     * Look up the referencing attributes to make sure they exist, and record
     * their attnums and type OIDs.
     */
    MemSet(pkattnum, 0, sizeof(pkattnum));
    MemSet(fkattnum, 0, sizeof(fkattnum));
    MemSet(pktypoid, 0, sizeof(pktypoid));
    MemSet(fktypoid, 0, sizeof(fktypoid));
    MemSet(opclasses, 0, sizeof(opclasses));
    MemSet(pfeqoperators, 0, sizeof(pfeqoperators));
    MemSet(ppeqoperators, 0, sizeof(ppeqoperators));
    MemSet(ffeqoperators, 0, sizeof(ffeqoperators));

    numfks = transformColumnNameList(RelationGetRelid(rel),
                                     fkconstraint->fk_attrs,
                                     fkattnum, fktypoid);

    /*
     * If the attribute list for the referenced table was omitted, lookup the
     * definition of the primary key and use it.  Otherwise, validate the
     * supplied attribute list.  In either case, discover the index OID and
     * index opclasses, and the attnums and type OIDs of the attributes.
     */
    if (fkconstraint->pk_attrs == NIL)
    {
        numpks = transformFkeyGetPrimaryKey(pkrel, &indexOid,
                                            &fkconstraint->pk_attrs,
                                            pkattnum, pktypoid,
                                            opclasses);
    }
    else
    {
        numpks = transformColumnNameList(RelationGetRelid(pkrel),
                                         fkconstraint->pk_attrs,
                                         pkattnum, pktypoid);
        /* Look for an index matching the column list */
        indexOid = transformFkeyCheckAttrs(pkrel, numpks, pkattnum,
                                           opclasses);
    }

    /*
     * Now we can check permissions.
     */
    checkFkeyPermissions(pkrel, pkattnum, numpks);
    checkFkeyPermissions(rel, fkattnum, numfks);

    /*
     * Look up the equality operators to use in the constraint.
     *
     * Note that we have to be careful about the difference between the actual
     * PK column type and the opclass' declared input type, which might be
     * only binary-compatible with it.  The declared opcintype is the right
     * thing to probe pg_amop with.
     */
    if (numfks != numpks)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_FOREIGN_KEY),
                 errmsg("number of referencing and referenced columns for foreign key disagree")));

    /*
     * On the strength of a previous constraint, we might avoid scanning
     * tables to validate this one.  See below.
     */
    old_check_ok = (fkconstraint->old_conpfeqop != NIL);
    Assert(!old_check_ok || numfks == list_length(fkconstraint->old_conpfeqop));

    for (i = 0; i < numpks; i++)
    {
        Oid         pktype = pktypoid[i];
        Oid         fktype = fktypoid[i];
        Oid         fktyped;
        HeapTuple   cla_ht;
        Form_pg_opclass cla_tup;
        Oid         amid;
        Oid         opfamily;
        Oid         opcintype;
        Oid         pfeqop;
        Oid         ppeqop;
        Oid         ffeqop;
        int16       eqstrategy;
        Oid         pfeqop_right;

        /* We need several fields out of the pg_opclass entry */
        cla_ht = SearchSysCache1(CLAOID, ObjectIdGetDatum(opclasses[i]));
        if (!HeapTupleIsValid(cla_ht))
            elog(ERROR, "cache lookup failed for opclass %u", opclasses[i]);
        cla_tup = (Form_pg_opclass) GETSTRUCT(cla_ht);
        amid = cla_tup->opcmethod;
        opfamily = cla_tup->opcfamily;
        opcintype = cla_tup->opcintype;
        ReleaseSysCache(cla_ht);

        /*
         * Check it's a btree; currently this can never fail since no other
         * index AMs support unique indexes.  If we ever did have other types
         * of unique indexes, we'd need a way to determine which operator
         * strategy number is equality.  (Is it reasonable to insist that
         * every such index AM use btree's number for equality?)
         */
        if (amid != BTREE_AM_OID)
            elog(ERROR, "only b-tree indexes are supported for foreign keys");
        eqstrategy = BTEqualStrategyNumber;

        /*
         * There had better be a primary equality operator for the index.
         * We'll use it for PK = PK comparisons.
         */
        ppeqop = get_opfamily_member(opfamily, opcintype, opcintype,
                                     eqstrategy);

        if (!OidIsValid(ppeqop))
            elog(ERROR, "missing operator %d(%u,%u) in opfamily %u",
                 eqstrategy, opcintype, opcintype, opfamily);

        /*
         * Are there equality operators that take exactly the FK type? Assume
         * we should look through any domain here.
         */
        fktyped = getBaseType(fktype);

        pfeqop = get_opfamily_member(opfamily, opcintype, fktyped,
                                     eqstrategy);
        if (OidIsValid(pfeqop))
        {
            pfeqop_right = fktyped;
            ffeqop = get_opfamily_member(opfamily, fktyped, fktyped,
                                         eqstrategy);
        }
        else
        {
            /* keep compiler quiet */
            pfeqop_right = InvalidOid;
            ffeqop = InvalidOid;
        }

        if (!(OidIsValid(pfeqop) && OidIsValid(ffeqop)))
        {
            /*
             * Otherwise, look for an implicit cast from the FK type to the
             * opcintype, and if found, use the primary equality operator.
             * This is a bit tricky because opcintype might be a polymorphic
             * type such as ANYARRAY or ANYENUM; so what we have to test is
             * whether the two actual column types can be concurrently cast to
             * that type.  (Otherwise, we'd fail to reject combinations such
             * as int[] and point[].)
             */
            Oid         input_typeids[2];
            Oid         target_typeids[2];

            input_typeids[0] = pktype;
            input_typeids[1] = fktype;
            target_typeids[0] = opcintype;
            target_typeids[1] = opcintype;
            if (can_coerce_type(2, input_typeids, target_typeids,
                                COERCION_IMPLICIT))
            {
                pfeqop = ffeqop = ppeqop;
                pfeqop_right = opcintype;
            }
        }

        if (!(OidIsValid(pfeqop) && OidIsValid(ffeqop)))
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
                     errmsg("foreign key constraint \"%s\" "
                            "cannot be implemented",
                            fkconstraint->conname),
                     errdetail("Key columns \"%s\" and \"%s\" "
                               "are of incompatible types: %s and %s.",
                               strVal(list_nth(fkconstraint->fk_attrs, i)),
                               strVal(list_nth(fkconstraint->pk_attrs, i)),
                               format_type_be(fktype),
                               format_type_be(pktype))));

        if (old_check_ok)
        {
            /*
             * When a pfeqop changes, revalidate the constraint.  We could
             * permit intra-opfamily changes, but that adds subtle complexity
             * without any concrete benefit for core types.  We need not
             * assess ppeqop or ffeqop, which RI_Initial_Check() does not use.
             */
            old_check_ok = (pfeqop == lfirst_oid(old_pfeqop_item));
            old_pfeqop_item = lnext(old_pfeqop_item);
        }
        if (old_check_ok)
        {
            Oid         old_fktype;
            Oid         new_fktype;
            CoercionPathType old_pathtype;
            CoercionPathType new_pathtype;
            Oid         old_castfunc;
            Oid         new_castfunc;

            /*
             * Identify coercion pathways from each of the old and new FK-side
             * column types to the right (foreign) operand type of the pfeqop.
             * We may assume that pg_constraint.conkey is not changing.
             */
            old_fktype = tab->oldDesc->attrs[fkattnum[i] - 1]->atttypid;
            new_fktype = fktype;
            old_pathtype = findFkeyCast(pfeqop_right, old_fktype,
                                        &old_castfunc);
            new_pathtype = findFkeyCast(pfeqop_right, new_fktype,
                                        &new_castfunc);

            /*
             * Upon a change to the cast from the FK column to its pfeqop
             * operand, revalidate the constraint.  For this evaluation, a
             * binary coercion cast is equivalent to no cast at all.  While
             * type implementors should design implicit casts with an eye
             * toward consistency of operations like equality, we cannot
             * assume here that they have done so.
             *
             * A function with a polymorphic argument could change behavior
             * arbitrarily in response to get_fn_expr_argtype().  Therefore,
             * when the cast destination is polymorphic, we only avoid
             * revalidation if the input type has not changed at all.  Given
             * just the core data types and operator classes, this requirement
             * prevents no would-be optimizations.
             *
             * If the cast converts from a base type to a domain thereon, then
             * that domain type must be the opcintype of the unique index.
             * Necessarily, the primary key column must then be of the domain
             * type.  Since the constraint was previously valid, all values on
             * the foreign side necessarily exist on the primary side and in
             * turn conform to the domain.  Consequently, we need not treat
             * domains specially here.
             *
             * Since we require that all collations share the same notion of
             * equality (which they do, because texteq reduces to bitwise
             * equality), we don't compare collation here.
             *
             * We need not directly consider the PK type.  It's necessarily
             * binary coercible to the opcintype of the unique index column,
             * and ri_triggers.c will only deal with PK datums in terms of
             * that opcintype.  Changing the opcintype also changes pfeqop.
             */
            old_check_ok = (new_pathtype == old_pathtype &&
                            new_castfunc == old_castfunc &&
                            (!IsPolymorphicType(pfeqop_right) ||
                             new_fktype == old_fktype));

        }

        pfeqoperators[i] = pfeqop;
        ppeqoperators[i] = ppeqop;
        ffeqoperators[i] = ffeqop;
    }

    /*
     * Record the FK constraint in pg_constraint.
     */
    constrOid = CreateConstraintEntry(fkconstraint->conname,
                                      RelationGetNamespace(rel),
                                      CONSTRAINT_FOREIGN,
                                      fkconstraint->deferrable,
                                      fkconstraint->initdeferred,
                                      fkconstraint->initially_valid,
                                      RelationGetRelid(rel),
                                      fkattnum,
                                      numfks,
                                      InvalidOid,       /* not a domain
                                                         * constraint */
                                      indexOid,
                                      RelationGetRelid(pkrel),
                                      pkattnum,
                                      pfeqoperators,
                                      ppeqoperators,
                                      ffeqoperators,
                                      numpks,
                                      fkconstraint->fk_upd_action,
                                      fkconstraint->fk_del_action,
                                      fkconstraint->fk_matchtype,
                                      NULL,     /* no exclusion constraint */
                                      NULL,     /* no check constraint */
                                      NULL,
                                      NULL,
                                      true,     /* islocal */
                                      0,        /* inhcount */
                                      true,     /* isnoinherit */
                                      false);   /* is_internal */

    /*
     * Create the triggers that will enforce the constraint.
     */
    createForeignKeyTriggers(rel, fkconstraint, constrOid, indexOid);

    /*
     * Tell Phase 3 to check that the constraint is satisfied by existing
     * rows. We can skip this during table creation, when requested explicitly
     * by specifying NOT VALID in an ADD FOREIGN KEY command, and when we're
     * recreating a constraint following a SET DATA TYPE operation that did
     * not impugn its validity.
     */
    if (!old_check_ok && !fkconstraint->skip_validation)
    {
        NewConstraint *newcon;

        newcon = (NewConstraint *) palloc0(sizeof(NewConstraint));
        newcon->name = fkconstraint->conname;
        newcon->contype = CONSTR_FOREIGN;
        newcon->refrelid = RelationGetRelid(pkrel);
        newcon->refindid = indexOid;
        newcon->conid = constrOid;
        newcon->qual = (Node *) fkconstraint;

        tab->constraints = lappend(tab->constraints, newcon);
    }

    /*
     * Close pk table, but keep lock until we've committed.
     */
    heap_close(pkrel, NoLock);
}

/*
 * ALTER TABLE VALIDATE CONSTRAINT
 *
 * XXX The reason we handle recursion here rather than at Phase 1 is because
 * there's no good way to skip recursing when handling foreign keys: there is
 * no need to lock children in that case, yet we wouldn't be able to avoid
 * doing so at that level.
 */
static void
ATExecValidateConstraint(Relation rel, char *constrName, bool recurse,
                         bool recursing, LOCKMODE lockmode)
{
    Relation    conrel;
    SysScanDesc scan;
    ScanKeyData key;
    HeapTuple   tuple;
    Form_pg_constraint con = NULL;
    bool        found = false;

    conrel = heap_open(ConstraintRelationId, RowExclusiveLock);

    /*
     * Find and check the target constraint
     */
    ScanKeyInit(&key,
                Anum_pg_constraint_conrelid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationGetRelid(rel)));
    scan = systable_beginscan(conrel, ConstraintRelidIndexId,
                              true, SnapshotNow, 1, &key);

    while (HeapTupleIsValid(tuple = systable_getnext(scan)))
    {
        con = (Form_pg_constraint) GETSTRUCT(tuple);
        if (strcmp(NameStr(con->conname), constrName) == 0)
        {
            found = true;
            break;
        }
    }

    if (!found)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("constraint \"%s\" of relation \"%s\" does not exist",
                        constrName, RelationGetRelationName(rel))));

    if (con->contype != CONSTRAINT_FOREIGN &&
        con->contype != CONSTRAINT_CHECK)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("constraint \"%s\" of relation \"%s\" is not a foreign key or check constraint",
                        constrName, RelationGetRelationName(rel))));

    if (!con->convalidated)
    {
        HeapTuple   copyTuple;
        Form_pg_constraint copy_con;

        if (con->contype == CONSTRAINT_FOREIGN)
        {
            Oid         conid = HeapTupleGetOid(tuple);
            Relation    refrel;

            /*
             * Triggers are already in place on both tables, so a concurrent
             * write that alters the result here is not possible. Normally we
             * can run a query here to do the validation, which would only
             * require AccessShareLock. In some cases, it is possible that we
             * might need to fire triggers to perform the check, so we take a
             * lock at RowShareLock level just in case.
             */
            refrel = heap_open(con->confrelid, RowShareLock);

            validateForeignKeyConstraint(constrName, rel, refrel,
                                         con->conindid,
                                         conid);
            heap_close(refrel, NoLock);

            /*
             * Foreign keys do not inherit, so we purposely ignore the
             * recursion bit here
             */
        }
        else if (con->contype == CONSTRAINT_CHECK)
        {
            List       *children = NIL;
            ListCell   *child;

            /*
             * If we're recursing, the parent has already done this, so skip
             * it.
             */
            if (!recursing)
                children = find_all_inheritors(RelationGetRelid(rel),
                                               lockmode, NULL);

            /*
             * For CHECK constraints, we must ensure that we only mark the
             * constraint as validated on the parent if it's already validated
             * on the children.
             *
             * We recurse before validating on the parent, to reduce risk of
             * deadlocks.
             */
            foreach(child, children)
            {
                Oid         childoid = lfirst_oid(child);
                Relation    childrel;

                if (childoid == RelationGetRelid(rel))
                    continue;

                /*
                 * If we are told not to recurse, there had better not be any
                 * child tables; else the addition would put them out of step.
                 */
                if (!recurse)
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                             errmsg("constraint must be validated on child tables too")));

                /* find_all_inheritors already got lock */
                childrel = heap_open(childoid, NoLock);

                ATExecValidateConstraint(childrel, constrName, false,
                                         true, lockmode);
                heap_close(childrel, NoLock);
            }

            validateCheckConstraint(rel, tuple);

            /*
             * Invalidate relcache so that others see the new validated
             * constraint.
             */
            CacheInvalidateRelcache(rel);
        }

        /*
         * Now update the catalog, while we have the door open.
         */
        copyTuple = heap_copytuple(tuple);
        copy_con = (Form_pg_constraint) GETSTRUCT(copyTuple);
        copy_con->convalidated = true;
        simple_heap_update(conrel, &copyTuple->t_self, copyTuple);
        CatalogUpdateIndexes(conrel, copyTuple);

        InvokeObjectPostAlterHook(ConstraintRelationId,
                                  HeapTupleGetOid(tuple), 0);

        heap_freetuple(copyTuple);
    }

    systable_endscan(scan);

    heap_close(conrel, RowExclusiveLock);
}


/*
 * transformColumnNameList - transform list of column names
 *
 * Lookup each name and return its attnum and type OID
 */
static int
transformColumnNameList(Oid relId, List *colList,
                        int16 *attnums, Oid *atttypids)
{
    ListCell   *l;
    int         attnum;

    attnum = 0;
    foreach(l, colList)
    {
        char       *attname = strVal(lfirst(l));
        HeapTuple   atttuple;

        atttuple = SearchSysCacheAttName(relId, attname);
        if (!HeapTupleIsValid(atttuple))
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_COLUMN),
                     errmsg("column \"%s\" referenced in foreign key constraint does not exist",
                            attname)));
        if (attnum >= INDEX_MAX_KEYS)
            ereport(ERROR,
                    (errcode(ERRCODE_TOO_MANY_COLUMNS),
                     errmsg("cannot have more than %d keys in a foreign key",
                            INDEX_MAX_KEYS)));
        attnums[attnum] = ((Form_pg_attribute) GETSTRUCT(atttuple))->attnum;
        atttypids[attnum] = ((Form_pg_attribute) GETSTRUCT(atttuple))->atttypid;
        ReleaseSysCache(atttuple);
        attnum++;
    }

    return attnum;
}

/*
 * transformFkeyGetPrimaryKey -
 *
 *  Look up the names, attnums, and types of the primary key attributes
 *  for the pkrel.  Also return the index OID and index opclasses of the
 *  index supporting the primary key.
 *
 *  All parameters except pkrel are output parameters.  Also, the function
 *  return value is the number of attributes in the primary key.
 *
 *  Used when the column list in the REFERENCES specification is omitted.
 */
static int
transformFkeyGetPrimaryKey(Relation pkrel, Oid *indexOid,
                           List **attnamelist,
                           int16 *attnums, Oid *atttypids,
                           Oid *opclasses)
{
    List       *indexoidlist;
    ListCell   *indexoidscan;
    HeapTuple   indexTuple = NULL;
    Form_pg_index indexStruct = NULL;
    Datum       indclassDatum;
    bool        isnull;
    oidvector  *indclass;
    int         i;

    /*
     * Get the list of index OIDs for the table from the relcache, and look up
     * each one in the pg_index syscache until we find one marked primary key
     * (hopefully there isn't more than one such).  Insist it's valid, too.
     */
    *indexOid = InvalidOid;

    indexoidlist = RelationGetIndexList(pkrel);

    foreach(indexoidscan, indexoidlist)
    {
        Oid         indexoid = lfirst_oid(indexoidscan);

        indexTuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(indexoid));
        if (!HeapTupleIsValid(indexTuple))
            elog(ERROR, "cache lookup failed for index %u", indexoid);
        indexStruct = (Form_pg_index) GETSTRUCT(indexTuple);
        if (indexStruct->indisprimary && IndexIsValid(indexStruct))
        {
            /*
             * Refuse to use a deferrable primary key.  This is per SQL spec,
             * and there would be a lot of interesting semantic problems if we
             * tried to allow it.
             */
            if (!indexStruct->indimmediate)
                ereport(ERROR,
                        (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                         errmsg("cannot use a deferrable primary key for referenced table \"%s\"",
                                RelationGetRelationName(pkrel))));

            *indexOid = indexoid;
            break;
        }
        ReleaseSysCache(indexTuple);
    }

    list_free(indexoidlist);

    /*
     * Check that we found it
     */
    if (!OidIsValid(*indexOid))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("there is no primary key for referenced table \"%s\"",
                        RelationGetRelationName(pkrel))));

    /* Must get indclass the hard way */
    indclassDatum = SysCacheGetAttr(INDEXRELID, indexTuple,
                                    Anum_pg_index_indclass, &isnull);
    Assert(!isnull);
    indclass = (oidvector *) DatumGetPointer(indclassDatum);

    /*
     * Now build the list of PK attributes from the indkey definition (we
     * assume a primary key cannot have expressional elements)
     */
    *attnamelist = NIL;
    for (i = 0; i < indexStruct->indnatts; i++)
    {
        int         pkattno = indexStruct->indkey.values[i];

        attnums[i] = pkattno;
        atttypids[i] = attnumTypeId(pkrel, pkattno);
        opclasses[i] = indclass->values[i];
        *attnamelist = lappend(*attnamelist,
               makeString(pstrdup(NameStr(*attnumAttName(pkrel, pkattno)))));
    }

    ReleaseSysCache(indexTuple);

    return i;
}

/*
 * transformFkeyCheckAttrs -
 *
 *  Make sure that the attributes of a referenced table belong to a unique
 *  (or primary key) constraint.  Return the OID of the index supporting
 *  the constraint, as well as the opclasses associated with the index
 *  columns.
 */
static Oid
transformFkeyCheckAttrs(Relation pkrel,
                        int numattrs, int16 *attnums,
                        Oid *opclasses) /* output parameter */
{
    Oid         indexoid = InvalidOid;
    bool        found = false;
    bool        found_deferrable = false;
    List       *indexoidlist;
    ListCell   *indexoidscan;

    /*
     * Get the list of index OIDs for the table from the relcache, and look up
     * each one in the pg_index syscache, and match unique indexes to the list
     * of attnums we are given.
     */
    indexoidlist = RelationGetIndexList(pkrel);

    foreach(indexoidscan, indexoidlist)
    {
        HeapTuple   indexTuple;
        Form_pg_index indexStruct;
        int         i,
                    j;

        indexoid = lfirst_oid(indexoidscan);
        indexTuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(indexoid));
        if (!HeapTupleIsValid(indexTuple))
            elog(ERROR, "cache lookup failed for index %u", indexoid);
        indexStruct = (Form_pg_index) GETSTRUCT(indexTuple);

        /*
         * Must have the right number of columns; must be unique and not a
         * partial index; forget it if there are any expressions, too. Invalid
         * indexes are out as well.
         */
        if (indexStruct->indnatts == numattrs &&
            indexStruct->indisunique &&
            IndexIsValid(indexStruct) &&
            heap_attisnull(indexTuple, Anum_pg_index_indpred) &&
            heap_attisnull(indexTuple, Anum_pg_index_indexprs))
        {
            /* Must get indclass the hard way */
            Datum       indclassDatum;
            bool        isnull;
            oidvector  *indclass;

            indclassDatum = SysCacheGetAttr(INDEXRELID, indexTuple,
                                            Anum_pg_index_indclass, &isnull);
            Assert(!isnull);
            indclass = (oidvector *) DatumGetPointer(indclassDatum);

            /*
             * The given attnum list may match the index columns in any order.
             * Check that each list is a subset of the other.
             */
            for (i = 0; i < numattrs; i++)
            {
                found = false;
                for (j = 0; j < numattrs; j++)
                {
                    if (attnums[i] == indexStruct->indkey.values[j])
                    {
                        found = true;
                        break;
                    }
                }
                if (!found)
                    break;
            }
            if (found)
            {
                for (i = 0; i < numattrs; i++)
                {
                    found = false;
                    for (j = 0; j < numattrs; j++)
                    {
                        if (attnums[j] == indexStruct->indkey.values[i])
                        {
                            opclasses[j] = indclass->values[i];
                            found = true;
                            break;
                        }
                    }
                    if (!found)
                        break;
                }
            }

            /*
             * Refuse to use a deferrable unique/primary key.  This is per SQL
             * spec, and there would be a lot of interesting semantic problems
             * if we tried to allow it.
             */
            if (found && !indexStruct->indimmediate)
            {
                /*
                 * Remember that we found an otherwise matching index, so that
                 * we can generate a more appropriate error message.
                 */
                found_deferrable = true;
                found = false;
            }
        }
        ReleaseSysCache(indexTuple);
        if (found)
            break;
    }

    if (!found)
    {
        if (found_deferrable)
            ereport(ERROR,
                    (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
                     errmsg("cannot use a deferrable unique constraint for referenced table \"%s\"",
                            RelationGetRelationName(pkrel))));
        else
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_FOREIGN_KEY),
                     errmsg("there is no unique constraint matching given keys for referenced table \"%s\"",
                            RelationGetRelationName(pkrel))));
    }

    list_free(indexoidlist);

    return indexoid;
}

/*
 * findFkeyCast -
 *
 *  Wrapper around find_coercion_pathway() for ATAddForeignKeyConstraint().
 *  Caller has equal regard for binary coercibility and for an exact match.
*/
static CoercionPathType
findFkeyCast(Oid targetTypeId, Oid sourceTypeId, Oid *funcid)
{
    CoercionPathType ret;

    if (targetTypeId == sourceTypeId)
    {
        ret = COERCION_PATH_RELABELTYPE;
        *funcid = InvalidOid;
    }
    else
    {
        ret = find_coercion_pathway(targetTypeId, sourceTypeId,
                                    COERCION_IMPLICIT, funcid);
        if (ret == COERCION_PATH_NONE)
            /* A previously-relied-upon cast is now gone. */
            elog(ERROR, "could not find cast from %u to %u",
                 sourceTypeId, targetTypeId);
    }

    return ret;
}

/* Permissions checks for ADD FOREIGN KEY */
static void
checkFkeyPermissions(Relation rel, int16 *attnums, int natts)
{
    Oid         roleid = GetUserId();
    AclResult   aclresult;
    int         i;

    /* Okay if we have relation-level REFERENCES permission */
    aclresult = pg_class_aclcheck(RelationGetRelid(rel), roleid,
                                  ACL_REFERENCES);
    if (aclresult == ACLCHECK_OK)
        return;
    /* Else we must have REFERENCES on each column */
    for (i = 0; i < natts; i++)
    {
        aclresult = pg_attribute_aclcheck(RelationGetRelid(rel), attnums[i],
                                          roleid, ACL_REFERENCES);
        if (aclresult != ACLCHECK_OK)
            aclcheck_error(aclresult, ACL_KIND_CLASS,
                           RelationGetRelationName(rel));
    }
}

/*
 * Scan the existing rows in a table to verify they meet a proposed
 * CHECK constraint.
 *
 * The caller must have opened and locked the relation appropriately.
 */
static void
validateCheckConstraint(Relation rel, HeapTuple constrtup)
{
    EState     *estate;
    Datum       val;
    char       *conbin;
    Expr       *origexpr;
    List       *exprstate;
    TupleDesc   tupdesc;
    HeapScanDesc scan;
    HeapTuple   tuple;
    ExprContext *econtext;
    MemoryContext oldcxt;
    TupleTableSlot *slot;
    Form_pg_constraint constrForm;
    bool        isnull;

    constrForm = (Form_pg_constraint) GETSTRUCT(constrtup);

    estate = CreateExecutorState();

    /*
     * XXX this tuple doesn't really come from a syscache, but this doesn't
     * matter to SysCacheGetAttr, because it only wants to be able to fetch
     * the tupdesc
     */
    val = SysCacheGetAttr(CONSTROID, constrtup, Anum_pg_constraint_conbin,
                          &isnull);
    if (isnull)
        elog(ERROR, "null conbin for constraint %u",
             HeapTupleGetOid(constrtup));
    conbin = TextDatumGetCString(val);
    origexpr = (Expr *) stringToNode(conbin);
    exprstate = (List *)
        ExecPrepareExpr((Expr *) make_ands_implicit(origexpr), estate);

    econtext = GetPerTupleExprContext(estate);
    tupdesc = RelationGetDescr(rel);
    slot = MakeSingleTupleTableSlot(tupdesc);
    econtext->ecxt_scantuple = slot;

    scan = heap_beginscan(rel, SnapshotNow, 0, NULL);

    /*
     * Switch to per-tuple memory context and reset it for each tuple
     * produced, so we don't leak memory.
     */
    oldcxt = MemoryContextSwitchTo(GetPerTupleMemoryContext(estate));

    while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
    {
        ExecStoreTuple(tuple, slot, InvalidBuffer, false);

        if (!ExecQual(exprstate, econtext, true))
            ereport(ERROR,
                    (errcode(ERRCODE_CHECK_VIOLATION),
                     errmsg("check constraint \"%s\" is violated by some row",
                            NameStr(constrForm->conname)),
                     errtableconstraint(rel, NameStr(constrForm->conname))));

        ResetExprContext(econtext);
    }

    MemoryContextSwitchTo(oldcxt);
    heap_endscan(scan);
    ExecDropSingleTupleTableSlot(slot);
    FreeExecutorState(estate);
}

/*
 * Scan the existing rows in a table to verify they meet a proposed FK
 * constraint.
 *
 * Caller must have opened and locked both relations appropriately.
 */
static void
validateForeignKeyConstraint(char *conname,
                             Relation rel,
                             Relation pkrel,
                             Oid pkindOid,
                             Oid constraintOid)
{
    HeapScanDesc scan;
    HeapTuple   tuple;
    Trigger     trig;

    ereport(DEBUG1,
            (errmsg("validating foreign key constraint \"%s\"", conname)));

    /*
     * Build a trigger call structure; we'll need it either way.
     */
    MemSet(&trig, 0, sizeof(trig));
    trig.tgoid = InvalidOid;
    trig.tgname = conname;
    trig.tgenabled = TRIGGER_FIRES_ON_ORIGIN;
    trig.tgisinternal = TRUE;
    trig.tgconstrrelid = RelationGetRelid(pkrel);
    trig.tgconstrindid = pkindOid;
    trig.tgconstraint = constraintOid;
    trig.tgdeferrable = FALSE;
    trig.tginitdeferred = FALSE;
    /* we needn't fill in tgargs or tgqual */

    /*
     * See if we can do it with a single LEFT JOIN query.  A FALSE result
     * indicates we must proceed with the fire-the-trigger method.
     */
    if (RI_Initial_Check(&trig, rel, pkrel))
        return;

    /*
     * Scan through each tuple, calling RI_FKey_check_ins (insert trigger) as
     * if that tuple had just been inserted.  If any of those fail, it should
     * ereport(ERROR) and that's that.
     */
    scan = heap_beginscan(rel, SnapshotNow, 0, NULL);

    while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
    {
        FunctionCallInfoData fcinfo;
        TriggerData trigdata;

        /*
         * Make a call to the trigger function
         *
         * No parameters are passed, but we do set a context
         */
        MemSet(&fcinfo, 0, sizeof(fcinfo));

        /*
         * We assume RI_FKey_check_ins won't look at flinfo...
         */
        trigdata.type = T_TriggerData;
        trigdata.tg_event = TRIGGER_EVENT_INSERT | TRIGGER_EVENT_ROW;
        trigdata.tg_relation = rel;
        trigdata.tg_trigtuple = tuple;
        trigdata.tg_newtuple = NULL;
        trigdata.tg_trigger = &trig;
        trigdata.tg_trigtuplebuf = scan->rs_cbuf;
        trigdata.tg_newtuplebuf = InvalidBuffer;

        fcinfo.context = (Node *) &trigdata;

        RI_FKey_check_ins(&fcinfo);
    }

    heap_endscan(scan);
}

static void
CreateFKCheckTrigger(RangeVar *myRel, Constraint *fkconstraint,
                     Oid constraintOid, Oid indexOid, bool on_insert)
{
    CreateTrigStmt *fk_trigger;

    /*
     * Note: for a self-referential FK (referencing and referenced tables are
     * the same), it is important that the ON UPDATE action fires before the
     * CHECK action, since both triggers will fire on the same row during an
     * UPDATE event; otherwise the CHECK trigger will be checking a non-final
     * state of the row.  Triggers fire in name order, so we ensure this by
     * using names like "RI_ConstraintTrigger_a_NNNN" for the action triggers
     * and "RI_ConstraintTrigger_c_NNNN" for the check triggers.
     */
    fk_trigger = makeNode(CreateTrigStmt);
    fk_trigger->trigname = "RI_ConstraintTrigger_c";
    fk_trigger->relation = myRel;
    fk_trigger->row = true;
    fk_trigger->timing = TRIGGER_TYPE_AFTER;

    /* Either ON INSERT or ON UPDATE */
    if (on_insert)
    {
        fk_trigger->funcname = SystemFuncName("RI_FKey_check_ins");
        fk_trigger->events = TRIGGER_TYPE_INSERT;
    }
    else
    {
        fk_trigger->funcname = SystemFuncName("RI_FKey_check_upd");
        fk_trigger->events = TRIGGER_TYPE_UPDATE;
    }

    fk_trigger->columns = NIL;
    fk_trigger->whenClause = NULL;
    fk_trigger->isconstraint = true;
    fk_trigger->deferrable = fkconstraint->deferrable;
    fk_trigger->initdeferred = fkconstraint->initdeferred;
    fk_trigger->constrrel = fkconstraint->pktable;
    fk_trigger->args = NIL;

    (void) CreateTrigger(fk_trigger, NULL, constraintOid, indexOid, true);

    /* Make changes-so-far visible */
    CommandCounterIncrement();
}

/*
 * Create the triggers that implement an FK constraint.
 */
static void
createForeignKeyTriggers(Relation rel, Constraint *fkconstraint,
                         Oid constraintOid, Oid indexOid)
{
    RangeVar   *myRel;
    CreateTrigStmt *fk_trigger;

    /*
     * Reconstruct a RangeVar for my relation (not passed in, unfortunately).
     */
    myRel = makeRangeVar(get_namespace_name(RelationGetNamespace(rel)),
                         pstrdup(RelationGetRelationName(rel)),
                         -1);

    /* Make changes-so-far visible */
    CommandCounterIncrement();

    /*
     * Build and execute a CREATE CONSTRAINT TRIGGER statement for the ON
     * DELETE action on the referenced table.
     */
    fk_trigger = makeNode(CreateTrigStmt);
    fk_trigger->trigname = "RI_ConstraintTrigger_a";
    fk_trigger->relation = fkconstraint->pktable;
    fk_trigger->row = true;
    fk_trigger->timing = TRIGGER_TYPE_AFTER;
    fk_trigger->events = TRIGGER_TYPE_DELETE;
    fk_trigger->columns = NIL;
    fk_trigger->whenClause = NULL;
    fk_trigger->isconstraint = true;
    fk_trigger->constrrel = myRel;
    switch (fkconstraint->fk_del_action)
    {
        case FKCONSTR_ACTION_NOACTION:
            fk_trigger->deferrable = fkconstraint->deferrable;
            fk_trigger->initdeferred = fkconstraint->initdeferred;
            fk_trigger->funcname = SystemFuncName("RI_FKey_noaction_del");
            break;
        case FKCONSTR_ACTION_RESTRICT:
            fk_trigger->deferrable = false;
            fk_trigger->initdeferred = false;
            fk_trigger->funcname = SystemFuncName("RI_FKey_restrict_del");
            break;
        case FKCONSTR_ACTION_CASCADE:
            fk_trigger->deferrable = false;
            fk_trigger->initdeferred = false;
            fk_trigger->funcname = SystemFuncName("RI_FKey_cascade_del");
            break;
        case FKCONSTR_ACTION_SETNULL:
            fk_trigger->deferrable = false;
            fk_trigger->initdeferred = false;
            fk_trigger->funcname = SystemFuncName("RI_FKey_setnull_del");
            break;
        case FKCONSTR_ACTION_SETDEFAULT:
            fk_trigger->deferrable = false;
            fk_trigger->initdeferred = false;
            fk_trigger->funcname = SystemFuncName("RI_FKey_setdefault_del");
            break;
        default:
            elog(ERROR, "unrecognized FK action type: %d",
                 (int) fkconstraint->fk_del_action);
            break;
    }
    fk_trigger->args = NIL;

    (void) CreateTrigger(fk_trigger, NULL, constraintOid, indexOid, true);

    /* Make changes-so-far visible */
    CommandCounterIncrement();

    /*
     * Build and execute a CREATE CONSTRAINT TRIGGER statement for the ON
     * UPDATE action on the referenced table.
     */
    fk_trigger = makeNode(CreateTrigStmt);
    fk_trigger->trigname = "RI_ConstraintTrigger_a";
    fk_trigger->relation = fkconstraint->pktable;
    fk_trigger->row = true;
    fk_trigger->timing = TRIGGER_TYPE_AFTER;
    fk_trigger->events = TRIGGER_TYPE_UPDATE;
    fk_trigger->columns = NIL;
    fk_trigger->whenClause = NULL;
    fk_trigger->isconstraint = true;
    fk_trigger->constrrel = myRel;
    switch (fkconstraint->fk_upd_action)
    {
        case FKCONSTR_ACTION_NOACTION:
            fk_trigger->deferrable = fkconstraint->deferrable;
            fk_trigger->initdeferred = fkconstraint->initdeferred;
            fk_trigger->funcname = SystemFuncName("RI_FKey_noaction_upd");
            break;
        case FKCONSTR_ACTION_RESTRICT:
            fk_trigger->deferrable = false;
            fk_trigger->initdeferred = false;
            fk_trigger->funcname = SystemFuncName("RI_FKey_restrict_upd");
            break;
        case FKCONSTR_ACTION_CASCADE:
            fk_trigger->deferrable = false;
            fk_trigger->initdeferred = false;
            fk_trigger->funcname = SystemFuncName("RI_FKey_cascade_upd");
            break;
        case FKCONSTR_ACTION_SETNULL:
            fk_trigger->deferrable = false;
            fk_trigger->initdeferred = false;
            fk_trigger->funcname = SystemFuncName("RI_FKey_setnull_upd");
            break;
        case FKCONSTR_ACTION_SETDEFAULT:
            fk_trigger->deferrable = false;
            fk_trigger->initdeferred = false;
            fk_trigger->funcname = SystemFuncName("RI_FKey_setdefault_upd");
            break;
        default:
            elog(ERROR, "unrecognized FK action type: %d",
                 (int) fkconstraint->fk_upd_action);
            break;
    }
    fk_trigger->args = NIL;

    (void) CreateTrigger(fk_trigger, NULL, constraintOid, indexOid, true);

    /* Make changes-so-far visible */
    CommandCounterIncrement();

    /*
     * Build and execute CREATE CONSTRAINT TRIGGER statements for the CHECK
     * action for both INSERTs and UPDATEs on the referencing table.
     */
    CreateFKCheckTrigger(myRel, fkconstraint, constraintOid, indexOid, true);
    CreateFKCheckTrigger(myRel, fkconstraint, constraintOid, indexOid, false);
}

/*
 * ALTER TABLE DROP CONSTRAINT
 *
 * Like DROP COLUMN, we can't use the normal ALTER TABLE recursion mechanism.
 */
static void
ATExecDropConstraint(Relation rel, const char *constrName,
                     DropBehavior behavior,
                     bool recurse, bool recursing,
                     bool missing_ok, LOCKMODE lockmode)
{
    List       *children;
    ListCell   *child;
    Relation    conrel;
    Form_pg_constraint con;
    SysScanDesc scan;
    ScanKeyData key;
    HeapTuple   tuple;
    bool        found = false;
    bool        is_no_inherit_constraint = false;

    /* At top level, permission check was done in ATPrepCmd, else do it */
    if (recursing)
        ATSimplePermissions(rel, ATT_TABLE);

    conrel = heap_open(ConstraintRelationId, RowExclusiveLock);

    /*
     * Find and drop the target constraint
     */
    ScanKeyInit(&key,
                Anum_pg_constraint_conrelid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationGetRelid(rel)));
    scan = systable_beginscan(conrel, ConstraintRelidIndexId,
                              true, SnapshotNow, 1, &key);

    while (HeapTupleIsValid(tuple = systable_getnext(scan)))
    {
        ObjectAddress conobj;

        con = (Form_pg_constraint) GETSTRUCT(tuple);

        if (strcmp(NameStr(con->conname), constrName) != 0)
            continue;

        /* Don't drop inherited constraints */
        if (con->coninhcount > 0 && !recursing)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                     errmsg("cannot drop inherited constraint \"%s\" of relation \"%s\"",
                            constrName, RelationGetRelationName(rel))));

        is_no_inherit_constraint = con->connoinherit;

        /*
         * Perform the actual constraint deletion
         */
        conobj.classId = ConstraintRelationId;
        conobj.objectId = HeapTupleGetOid(tuple);
        conobj.objectSubId = 0;

        performDeletion(&conobj, behavior, 0);

        found = true;

        /* constraint found and dropped -- no need to keep looping */
        break;
    }

    systable_endscan(scan);

    if (!found)
    {
        if (!missing_ok)
        {
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_OBJECT),
                errmsg("constraint \"%s\" of relation \"%s\" does not exist",
                       constrName, RelationGetRelationName(rel))));
        }
        else
        {
            ereport(NOTICE,
                    (errmsg("constraint \"%s\" of relation \"%s\" does not exist, skipping",
                            constrName, RelationGetRelationName(rel))));
            heap_close(conrel, RowExclusiveLock);
            return;
        }
    }

    /*
     * Propagate to children as appropriate.  Unlike most other ALTER
     * routines, we have to do this one level of recursion at a time; we can't
     * use find_all_inheritors to do it in one pass.
     */
    if (!is_no_inherit_constraint)
        children = find_inheritance_children(RelationGetRelid(rel), lockmode);
    else
        children = NIL;

    foreach(child, children)
    {
        Oid         childrelid = lfirst_oid(child);
        Relation    childrel;
        HeapTuple   copy_tuple;

        /* find_inheritance_children already got lock */
        childrel = heap_open(childrelid, NoLock);
        CheckTableNotInUse(childrel, "ALTER TABLE");

        ScanKeyInit(&key,
                    Anum_pg_constraint_conrelid,
                    BTEqualStrategyNumber, F_OIDEQ,
                    ObjectIdGetDatum(childrelid));
        scan = systable_beginscan(conrel, ConstraintRelidIndexId,
                                  true, SnapshotNow, 1, &key);

        /* scan for matching tuple - there should only be one */
        while (HeapTupleIsValid(tuple = systable_getnext(scan)))
        {
            con = (Form_pg_constraint) GETSTRUCT(tuple);

            /* Right now only CHECK constraints can be inherited */
            if (con->contype != CONSTRAINT_CHECK)
                continue;

            if (strcmp(NameStr(con->conname), constrName) == 0)
                break;
        }

        if (!HeapTupleIsValid(tuple))
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_OBJECT),
                errmsg("constraint \"%s\" of relation \"%s\" does not exist",
                       constrName,
                       RelationGetRelationName(childrel))));

        copy_tuple = heap_copytuple(tuple);

        systable_endscan(scan);

        con = (Form_pg_constraint) GETSTRUCT(copy_tuple);

        if (con->coninhcount <= 0)      /* shouldn't happen */
            elog(ERROR, "relation %u has non-inherited constraint \"%s\"",
                 childrelid, constrName);

        if (recurse)
        {
            /*
             * If the child constraint has other definition sources, just
             * decrement its inheritance count; if not, recurse to delete it.
             */
            if (con->coninhcount == 1 && !con->conislocal)
            {
                /* Time to delete this child constraint, too */
                ATExecDropConstraint(childrel, constrName, behavior,
                                     true, true,
                                     false, lockmode);
            }
            else
            {
                /* Child constraint must survive my deletion */
                con->coninhcount--;
                simple_heap_update(conrel, &copy_tuple->t_self, copy_tuple);
                CatalogUpdateIndexes(conrel, copy_tuple);

                /* Make update visible */
                CommandCounterIncrement();
            }
        }
        else
        {
            /*
             * If we were told to drop ONLY in this table (no recursion), we
             * need to mark the inheritors' constraints as locally defined
             * rather than inherited.
             */
            con->coninhcount--;
            con->conislocal = true;

            simple_heap_update(conrel, &copy_tuple->t_self, copy_tuple);
            CatalogUpdateIndexes(conrel, copy_tuple);

            /* Make update visible */
            CommandCounterIncrement();
        }

        heap_freetuple(copy_tuple);

        heap_close(childrel, NoLock);
    }

    heap_close(conrel, RowExclusiveLock);
}

/*
 * ALTER COLUMN TYPE
 */
static void
ATPrepAlterColumnType(List **wqueue,
                      AlteredTableInfo *tab, Relation rel,
                      bool recurse, bool recursing,
                      AlterTableCmd *cmd, LOCKMODE lockmode)
{
    char       *colName = cmd->name;
    ColumnDef  *def = (ColumnDef *) cmd->def;
    TypeName   *typeName = def->typeName;
    Node       *transform = def->raw_default;
    HeapTuple   tuple;
    Form_pg_attribute attTup;
    AttrNumber  attnum;
    Oid         targettype;
    int32       targettypmod;
    Oid         targetcollid;
    NewColumnValue *newval;
    ParseState *pstate = make_parsestate(NULL);
    AclResult   aclresult;

    if (rel->rd_rel->reloftype && !recursing)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("cannot alter column type of typed table")));

    /* lookup the attribute so we can check inheritance status */
    tuple = SearchSysCacheAttName(RelationGetRelid(rel), colName);
    if (!HeapTupleIsValid(tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_COLUMN),
                 errmsg("column \"%s\" of relation \"%s\" does not exist",
                        colName, RelationGetRelationName(rel))));
    attTup = (Form_pg_attribute) GETSTRUCT(tuple);
    attnum = attTup->attnum;

    /* Can't alter a system attribute */
    if (attnum <= 0)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot alter system column \"%s\"",
                        colName)));

    /* Don't alter inherited columns */
    if (attTup->attinhcount > 0 && !recursing)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                 errmsg("cannot alter inherited column \"%s\"",
                        colName)));

    /* Look up the target type */
    typenameTypeIdAndMod(NULL, typeName, &targettype, &targettypmod);

    aclresult = pg_type_aclcheck(targettype, GetUserId(), ACL_USAGE);
    if (aclresult != ACLCHECK_OK)
        aclcheck_error_type(aclresult, targettype);

    /* And the collation */
    targetcollid = GetColumnDefCollation(NULL, def, targettype);

    /* make sure datatype is legal for a column */
    CheckAttributeType(colName, targettype, targetcollid,
                       list_make1_oid(rel->rd_rel->reltype),
                       false);

    if (tab->relkind == RELKIND_RELATION)
    {
        /*
         * Set up an expression to transform the old data value to the new
         * type. If a USING option was given, transform and use that
         * expression, else just take the old value and try to coerce it.  We
         * do this first so that type incompatibility can be detected before
         * we waste effort, and because we need the expression to be parsed
         * against the original table row type.
         */
        if (transform)
        {
            RangeTblEntry *rte;

            /* Expression must be able to access vars of old table */
            rte = addRangeTableEntryForRelation(pstate,
                                                rel,
                                                NULL,
                                                false,
                                                true);
            addRTEtoQuery(pstate, rte, false, true, true);

            transform = transformExpr(pstate, transform,
                                      EXPR_KIND_ALTER_COL_TRANSFORM);

            /* It can't return a set */
            if (expression_returns_set(transform))
                ereport(ERROR,
                        (errcode(ERRCODE_DATATYPE_MISMATCH),
                      errmsg("transform expression must not return a set")));
        }
        else
        {
            transform = (Node *) makeVar(1, attnum,
                                         attTup->atttypid, attTup->atttypmod,
                                         attTup->attcollation,
                                         0);
        }

        transform = coerce_to_target_type(pstate,
                                          transform, exprType(transform),
                                          targettype, targettypmod,
                                          COERCION_ASSIGNMENT,
                                          COERCE_IMPLICIT_CAST,
                                          -1);
        if (transform == NULL)
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
              errmsg("column \"%s\" cannot be cast automatically to type %s",
                     colName, format_type_be(targettype)),
                     errhint("Specify a USING expression to perform the conversion.")));

        /* Fix collations after all else */
        assign_expr_collations(pstate, transform);

        /* Plan the expr now so we can accurately assess the need to rewrite. */
        transform = (Node *) expression_planner((Expr *) transform);

        /*
         * Add a work queue item to make ATRewriteTable update the column
         * contents.
         */
        newval = (NewColumnValue *) palloc0(sizeof(NewColumnValue));
        newval->attnum = attnum;
        newval->expr = (Expr *) transform;

        tab->newvals = lappend(tab->newvals, newval);
        if (ATColumnChangeRequiresRewrite(transform, attnum))
            tab->rewrite = true;
    }
    else if (transform)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not a table",
                        RelationGetRelationName(rel))));

    if (tab->relkind == RELKIND_COMPOSITE_TYPE ||
        tab->relkind == RELKIND_FOREIGN_TABLE)
    {
        /*
         * For composite types, do this check now.  Tables will check it later
         * when the table is being rewritten.
         */
        find_composite_type_dependencies(rel->rd_rel->reltype, rel, NULL);
    }

    ReleaseSysCache(tuple);

    /*
     * The recursion case is handled by ATSimpleRecursion.  However, if we are
     * told not to recurse, there had better not be any child tables; else the
     * alter would put them out of step.
     */
    if (recurse)
        ATSimpleRecursion(wqueue, rel, cmd, recurse, lockmode);
    else if (!recursing &&
             find_inheritance_children(RelationGetRelid(rel), NoLock) != NIL)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_TABLE_DEFINITION),
                 errmsg("type of inherited column \"%s\" must be changed in child tables too",
                        colName)));

    if (tab->relkind == RELKIND_COMPOSITE_TYPE)
        ATTypedTableRecursion(wqueue, rel, cmd, lockmode);
}

/*
 * When the data type of a column is changed, a rewrite might not be required
 * if the new type is sufficiently identical to the old one, and the USING
 * clause isn't trying to insert some other value.  It's safe to skip the
 * rewrite if the old type is binary coercible to the new type, or if the
 * new type is an unconstrained domain over the old type.  In the case of a
 * constrained domain, we could get by with scanning the table and checking
 * the constraint rather than actually rewriting it, but we don't currently
 * try to do that.
 */
static bool
ATColumnChangeRequiresRewrite(Node *expr, AttrNumber varattno)
{
    Assert(expr != NULL);

    for (;;)
    {
        /* only one varno, so no need to check that */
        if (IsA(expr, Var) &&((Var *) expr)->varattno == varattno)
            return false;
        else if (IsA(expr, RelabelType))
            expr = (Node *) ((RelabelType *) expr)->arg;
        else if (IsA(expr, CoerceToDomain))
        {
            CoerceToDomain *d = (CoerceToDomain *) expr;

            if (GetDomainConstraints(d->resulttype) != NIL)
                return true;
            expr = (Node *) d->arg;
        }
        else
            return true;
    }
}

static void
ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
                      AlterTableCmd *cmd, LOCKMODE lockmode)
{
    char       *colName = cmd->name;
    ColumnDef  *def = (ColumnDef *) cmd->def;
    TypeName   *typeName = def->typeName;
    HeapTuple   heapTup;
    Form_pg_attribute attTup;
    AttrNumber  attnum;
    HeapTuple   typeTuple;
    Form_pg_type tform;
    Oid         targettype;
    int32       targettypmod;
    Oid         targetcollid;
    Node       *defaultexpr;
    Relation    attrelation;
    Relation    depRel;
    ScanKeyData key[3];
    SysScanDesc scan;
    HeapTuple   depTup;

    attrelation = heap_open(AttributeRelationId, RowExclusiveLock);

    /* Look up the target column */
    heapTup = SearchSysCacheCopyAttName(RelationGetRelid(rel), colName);
    if (!HeapTupleIsValid(heapTup))     /* shouldn't happen */
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_COLUMN),
                 errmsg("column \"%s\" of relation \"%s\" does not exist",
                        colName, RelationGetRelationName(rel))));
    attTup = (Form_pg_attribute) GETSTRUCT(heapTup);
    attnum = attTup->attnum;

    /* Check for multiple ALTER TYPE on same column --- can't cope */
    if (attTup->atttypid != tab->oldDesc->attrs[attnum - 1]->atttypid ||
        attTup->atttypmod != tab->oldDesc->attrs[attnum - 1]->atttypmod)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot alter type of column \"%s\" twice",
                        colName)));

    /* Look up the target type (should not fail, since prep found it) */
    typeTuple = typenameType(NULL, typeName, &targettypmod);
    tform = (Form_pg_type) GETSTRUCT(typeTuple);
    targettype = HeapTupleGetOid(typeTuple);
    /* And the collation */
    targetcollid = GetColumnDefCollation(NULL, def, targettype);

    /*
     * If there is a default expression for the column, get it and ensure we
     * can coerce it to the new datatype.  (We must do this before changing
     * the column type, because build_column_default itself will try to
     * coerce, and will not issue the error message we want if it fails.)
     *
     * We remove any implicit coercion steps at the top level of the old
     * default expression; this has been agreed to satisfy the principle of
     * least surprise.  (The conversion to the new column type should act like
     * it started from what the user sees as the stored expression, and the
     * implicit coercions aren't going to be shown.)
     */
    if (attTup->atthasdef)
    {
        defaultexpr = build_column_default(rel, attnum);
        Assert(defaultexpr);
        defaultexpr = strip_implicit_coercions(defaultexpr);
        defaultexpr = coerce_to_target_type(NULL,       /* no UNKNOWN params */
                                          defaultexpr, exprType(defaultexpr),
                                            targettype, targettypmod,
                                            COERCION_ASSIGNMENT,
                                            COERCE_IMPLICIT_CAST,
                                            -1);
        if (defaultexpr == NULL)
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
                     errmsg("default for column \"%s\" cannot be cast automatically to type %s",
                            colName, format_type_be(targettype))));
    }
    else
        defaultexpr = NULL;

    /*
     * Find everything that depends on the column (constraints, indexes, etc),
     * and record enough information to let us recreate the objects.
     *
     * The actual recreation does not happen here, but only after we have
     * performed all the individual ALTER TYPE operations.  We have to save
     * the info before executing ALTER TYPE, though, else the deparser will
     * get confused.
     *
     * There could be multiple entries for the same object, so we must check
     * to ensure we process each one only once.  Note: we assume that an index
     * that implements a constraint will not show a direct dependency on the
     * column.
     */
    depRel = heap_open(DependRelationId, RowExclusiveLock);

    ScanKeyInit(&key[0],
                Anum_pg_depend_refclassid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationRelationId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_refobjid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationGetRelid(rel)));
    ScanKeyInit(&key[2],
                Anum_pg_depend_refobjsubid,
                BTEqualStrategyNumber, F_INT4EQ,
                Int32GetDatum((int32) attnum));

    scan = systable_beginscan(depRel, DependReferenceIndexId, true,
                              SnapshotNow, 3, key);

    while (HeapTupleIsValid(depTup = systable_getnext(scan)))
    {
        Form_pg_depend foundDep = (Form_pg_depend) GETSTRUCT(depTup);
        ObjectAddress foundObject;

        /* We don't expect any PIN dependencies on columns */
        if (foundDep->deptype == DEPENDENCY_PIN)
            elog(ERROR, "cannot alter type of a pinned column");

        foundObject.classId = foundDep->classid;
        foundObject.objectId = foundDep->objid;
        foundObject.objectSubId = foundDep->objsubid;

        switch (getObjectClass(&foundObject))
        {
            case OCLASS_CLASS:
                {
                    char        relKind = get_rel_relkind(foundObject.objectId);

                    if (relKind == RELKIND_INDEX)
                    {
                        Assert(foundObject.objectSubId == 0);
                        if (!list_member_oid(tab->changedIndexOids, foundObject.objectId))
                        {
                            tab->changedIndexOids = lappend_oid(tab->changedIndexOids,
                                                       foundObject.objectId);
                            tab->changedIndexDefs = lappend(tab->changedIndexDefs,
                               pg_get_indexdef_string(foundObject.objectId));
                        }
                    }
                    else if (relKind == RELKIND_SEQUENCE)
                    {
                        /*
                         * This must be a SERIAL column's sequence.  We need
                         * not do anything to it.
                         */
                        Assert(foundObject.objectSubId == 0);
                    }
                    else
                    {
                        /* Not expecting any other direct dependencies... */
                        elog(ERROR, "unexpected object depending on column: %s",
                             getObjectDescription(&foundObject));
                    }
                    break;
                }

            case OCLASS_CONSTRAINT:
                Assert(foundObject.objectSubId == 0);
                if (!list_member_oid(tab->changedConstraintOids,
                                     foundObject.objectId))
                {
                    char       *defstring = pg_get_constraintdef_string(foundObject.objectId);

                    /*
                     * Put NORMAL dependencies at the front of the list and
                     * AUTO dependencies at the back.  This makes sure that
                     * foreign-key constraints depending on this column will
                     * be dropped before unique or primary-key constraints of
                     * the column; which we must have because the FK
                     * constraints depend on the indexes belonging to the
                     * unique constraints.
                     */
                    if (foundDep->deptype == DEPENDENCY_NORMAL)
                    {
                        tab->changedConstraintOids =
                            lcons_oid(foundObject.objectId,
                                      tab->changedConstraintOids);
                        tab->changedConstraintDefs =
                            lcons(defstring,
                                  tab->changedConstraintDefs);
                    }
                    else
                    {
                        tab->changedConstraintOids =
                            lappend_oid(tab->changedConstraintOids,
                                        foundObject.objectId);
                        tab->changedConstraintDefs =
                            lappend(tab->changedConstraintDefs,
                                    defstring);
                    }
                }
                break;

            case OCLASS_REWRITE:
                /* XXX someday see if we can cope with revising views */
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("cannot alter type of a column used by a view or rule"),
                         errdetail("%s depends on column \"%s\"",
                                   getObjectDescription(&foundObject),
                                   colName)));
                break;

            case OCLASS_TRIGGER:

                /*
                 * A trigger can depend on a column because the column is
                 * specified as an update target, or because the column is
                 * used in the trigger's WHEN condition.  The first case would
                 * not require any extra work, but the second case would
                 * require updating the WHEN expression, which will take a
                 * significant amount of new code.  Since we can't easily tell
                 * which case applies, we punt for both.  FIXME someday.
                 */
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("cannot alter type of a column used in a trigger definition"),
                         errdetail("%s depends on column \"%s\"",
                                   getObjectDescription(&foundObject),
                                   colName)));
                break;

            case OCLASS_DEFAULT:

                /*
                 * Ignore the column's default expression, since we will fix
                 * it below.
                 */
                Assert(defaultexpr);
                break;

            case OCLASS_PROC:
            case OCLASS_TYPE:
            case OCLASS_CAST:
            case OCLASS_COLLATION:
            case OCLASS_CONVERSION:
            case OCLASS_LANGUAGE:
            case OCLASS_LARGEOBJECT:
            case OCLASS_OPERATOR:
            case OCLASS_OPCLASS:
            case OCLASS_OPFAMILY:
            case OCLASS_AMOP:
            case OCLASS_AMPROC:
            case OCLASS_SCHEMA:
            case OCLASS_TSPARSER:
            case OCLASS_TSDICT:
            case OCLASS_TSTEMPLATE:
            case OCLASS_TSCONFIG:
            case OCLASS_ROLE:
            case OCLASS_DATABASE:
            case OCLASS_TBLSPACE:
            case OCLASS_FDW:
            case OCLASS_FOREIGN_SERVER:
            case OCLASS_USER_MAPPING:
            case OCLASS_DEFACL:
            case OCLASS_EXTENSION:

                /*
                 * We don't expect any of these sorts of objects to depend on
                 * a column.
                 */
                elog(ERROR, "unexpected object depending on column: %s",
                     getObjectDescription(&foundObject));
                break;

            default:
                elog(ERROR, "unrecognized object class: %u",
                     foundObject.classId);
        }
    }

    systable_endscan(scan);

    /*
     * Now scan for dependencies of this column on other things.  The only
     * thing we should find is the dependency on the column datatype, which we
     * want to remove, and possibly a collation dependency.
     */
    ScanKeyInit(&key[0],
                Anum_pg_depend_classid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationRelationId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_objid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationGetRelid(rel)));
    ScanKeyInit(&key[2],
                Anum_pg_depend_objsubid,
                BTEqualStrategyNumber, F_INT4EQ,
                Int32GetDatum((int32) attnum));

    scan = systable_beginscan(depRel, DependDependerIndexId, true,
                              SnapshotNow, 3, key);

    while (HeapTupleIsValid(depTup = systable_getnext(scan)))
    {
        Form_pg_depend foundDep = (Form_pg_depend) GETSTRUCT(depTup);

        if (foundDep->deptype != DEPENDENCY_NORMAL)
            elog(ERROR, "found unexpected dependency type '%c'",
                 foundDep->deptype);
        if (!(foundDep->refclassid == TypeRelationId &&
              foundDep->refobjid == attTup->atttypid) &&
            !(foundDep->refclassid == CollationRelationId &&
              foundDep->refobjid == attTup->attcollation))
            elog(ERROR, "found unexpected dependency for column");

        simple_heap_delete(depRel, &depTup->t_self);
    }

    systable_endscan(scan);

    heap_close(depRel, RowExclusiveLock);

    /*
     * Here we go --- change the recorded column type and collation.  (Note
     * heapTup is a copy of the syscache entry, so okay to scribble on.)
     */
    attTup->atttypid = targettype;
    attTup->atttypmod = targettypmod;
    attTup->attcollation = targetcollid;
    attTup->attndims = list_length(typeName->arrayBounds);
    attTup->attlen = tform->typlen;
    attTup->attbyval = tform->typbyval;
    attTup->attalign = tform->typalign;
    attTup->attstorage = tform->typstorage;

    ReleaseSysCache(typeTuple);

    simple_heap_update(attrelation, &heapTup->t_self, heapTup);

    /* keep system catalog indexes current */
    CatalogUpdateIndexes(attrelation, heapTup);

    heap_close(attrelation, RowExclusiveLock);

    /* Install dependencies on new datatype and collation */
    add_column_datatype_dependency(RelationGetRelid(rel), attnum, targettype);
    add_column_collation_dependency(RelationGetRelid(rel), attnum, targetcollid);

    /*
     * Drop any pg_statistic entry for the column, since it's now wrong type
     */
    RemoveStatistics(RelationGetRelid(rel), attnum);

    InvokeObjectPostAlterHook(RelationRelationId,
                              RelationGetRelid(rel), attnum);

    /*
     * Update the default, if present, by brute force --- remove and re-add
     * the default.  Probably unsafe to take shortcuts, since the new version
     * may well have additional dependencies.  (It's okay to do this now,
     * rather than after other ALTER TYPE commands, since the default won't
     * depend on other column types.)
     */
    if (defaultexpr)
    {
        /* Must make new row visible since it will be updated again */
        CommandCounterIncrement();

        /*
         * We use RESTRICT here for safety, but at present we do not expect
         * anything to depend on the default.
         */
        RemoveAttrDefault(RelationGetRelid(rel), attnum, DROP_RESTRICT, true,
                          true);

        StoreAttrDefault(rel, attnum, defaultexpr, true);
    }

    /* Cleanup */
    heap_freetuple(heapTup);
}

static void
ATExecAlterColumnGenericOptions(Relation rel,
                                const char *colName,
                                List *options,
                                LOCKMODE lockmode)
{
    Relation    ftrel;
    Relation    attrel;
    ForeignServer *server;
    ForeignDataWrapper *fdw;
    HeapTuple   tuple;
    HeapTuple   newtuple;
    bool        isnull;
    Datum       repl_val[Natts_pg_attribute];
    bool        repl_null[Natts_pg_attribute];
    bool        repl_repl[Natts_pg_attribute];
    Datum       datum;
    Form_pg_foreign_table fttableform;
    Form_pg_attribute atttableform;

    if (options == NIL)
        return;

    /* First, determine FDW validator associated to the foreign table. */
    ftrel = heap_open(ForeignTableRelationId, AccessShareLock);
    tuple = SearchSysCache1(FOREIGNTABLEREL, rel->rd_id);
    if (!HeapTupleIsValid(tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("foreign table \"%s\" does not exist",
                        RelationGetRelationName(rel))));
    fttableform = (Form_pg_foreign_table) GETSTRUCT(tuple);
    server = GetForeignServer(fttableform->ftserver);
    fdw = GetForeignDataWrapper(server->fdwid);

    heap_close(ftrel, AccessShareLock);
    ReleaseSysCache(tuple);

    attrel = heap_open(AttributeRelationId, RowExclusiveLock);
    tuple = SearchSysCacheAttName(RelationGetRelid(rel), colName);
    if (!HeapTupleIsValid(tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_COLUMN),
                 errmsg("column \"%s\" of relation \"%s\" does not exist",
                        colName, RelationGetRelationName(rel))));

    /* Prevent them from altering a system attribute */
    atttableform = (Form_pg_attribute) GETSTRUCT(tuple);
    if (atttableform->attnum <= 0)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot alter system column \"%s\"", colName)));


    /* Initialize buffers for new tuple values */
    memset(repl_val, 0, sizeof(repl_val));
    memset(repl_null, false, sizeof(repl_null));
    memset(repl_repl, false, sizeof(repl_repl));

    /* Extract the current options */
    datum = SysCacheGetAttr(ATTNAME,
                            tuple,
                            Anum_pg_attribute_attfdwoptions,
                            &isnull);
    if (isnull)
        datum = PointerGetDatum(NULL);

    /* Transform the options */
    datum = transformGenericOptions(AttributeRelationId,
                                    datum,
                                    options,
                                    fdw->fdwvalidator);

    if (PointerIsValid(DatumGetPointer(datum)))
        repl_val[Anum_pg_attribute_attfdwoptions - 1] = datum;
    else
        repl_null[Anum_pg_attribute_attfdwoptions - 1] = true;

    repl_repl[Anum_pg_attribute_attfdwoptions - 1] = true;

    /* Everything looks good - update the tuple */

    newtuple = heap_modify_tuple(tuple, RelationGetDescr(attrel),
                                 repl_val, repl_null, repl_repl);

    simple_heap_update(attrel, &newtuple->t_self, newtuple);
    CatalogUpdateIndexes(attrel, newtuple);

    InvokeObjectPostAlterHook(RelationRelationId,
                              RelationGetRelid(rel),
                              atttableform->attnum);

    ReleaseSysCache(tuple);

    heap_close(attrel, RowExclusiveLock);

    heap_freetuple(newtuple);
}

/*
 * Cleanup after we've finished all the ALTER TYPE operations for a
 * particular relation.  We have to drop and recreate all the indexes
 * and constraints that depend on the altered columns.
 */
static void
ATPostAlterTypeCleanup(List **wqueue, AlteredTableInfo *tab, LOCKMODE lockmode)
{
    ObjectAddress obj;
    ListCell   *def_item;
    ListCell   *oid_item;

    /*
     * Re-parse the index and constraint definitions, and attach them to the
     * appropriate work queue entries.  We do this before dropping because in
     * the case of a FOREIGN KEY constraint, we might not yet have exclusive
     * lock on the table the constraint is attached to, and we need to get
     * that before dropping.  It's safe because the parser won't actually look
     * at the catalogs to detect the existing entry.
     */
    forboth(oid_item, tab->changedConstraintOids,
            def_item, tab->changedConstraintDefs)
        ATPostAlterTypeParse(lfirst_oid(oid_item), (char *) lfirst(def_item),
                             wqueue, lockmode, tab->rewrite);
    forboth(oid_item, tab->changedIndexOids,
            def_item, tab->changedIndexDefs)
        ATPostAlterTypeParse(lfirst_oid(oid_item), (char *) lfirst(def_item),
                             wqueue, lockmode, tab->rewrite);

    /*
     * Now we can drop the existing constraints and indexes --- constraints
     * first, since some of them might depend on the indexes.  In fact, we
     * have to delete FOREIGN KEY constraints before UNIQUE constraints, but
     * we already ordered the constraint list to ensure that would happen. It
     * should be okay to use DROP_RESTRICT here, since nothing else should be
     * depending on these objects.
     */
    foreach(oid_item, tab->changedConstraintOids)
    {
        obj.classId = ConstraintRelationId;
        obj.objectId = lfirst_oid(oid_item);
        obj.objectSubId = 0;
        performDeletion(&obj, DROP_RESTRICT, PERFORM_DELETION_INTERNAL);
    }

    foreach(oid_item, tab->changedIndexOids)
    {
        obj.classId = RelationRelationId;
        obj.objectId = lfirst_oid(oid_item);
        obj.objectSubId = 0;
        performDeletion(&obj, DROP_RESTRICT, PERFORM_DELETION_INTERNAL);
    }

    /*
     * The objects will get recreated during subsequent passes over the work
     * queue.
     */
}

static void
ATPostAlterTypeParse(Oid oldId, char *cmd,
                     List **wqueue, LOCKMODE lockmode, bool rewrite)
{
    List       *raw_parsetree_list;
    List       *querytree_list;
    ListCell   *list_item;

    /*
     * We expect that we will get only ALTER TABLE and CREATE INDEX
     * statements. Hence, there is no need to pass them through
     * parse_analyze() or the rewriter, but instead we need to pass them
     * through parse_utilcmd.c to make them ready for execution.
     */
    raw_parsetree_list = raw_parser(cmd);
    querytree_list = NIL;
    foreach(list_item, raw_parsetree_list)
    {
        Node       *stmt = (Node *) lfirst(list_item);

        if (IsA(stmt, IndexStmt))
            querytree_list = lappend(querytree_list,
                                     transformIndexStmt((IndexStmt *) stmt,
                                                        cmd));
        else if (IsA(stmt, AlterTableStmt))
            querytree_list = list_concat(querytree_list,
                             transformAlterTableStmt((AlterTableStmt *) stmt,
                                                     cmd));
        else
            querytree_list = lappend(querytree_list, stmt);
    }

    /*
     * Attach each generated command to the proper place in the work queue.
     * Note this could result in creation of entirely new work-queue entries.
     *
     * Also note that we have to tweak the command subtypes, because it turns
     * out that re-creation of indexes and constraints has to act a bit
     * differently from initial creation.
     */
    foreach(list_item, querytree_list)
    {
        Node       *stm = (Node *) lfirst(list_item);
        Relation    rel;
        AlteredTableInfo *tab;

        switch (nodeTag(stm))
        {
            case T_IndexStmt:
                {
                    IndexStmt  *stmt = (IndexStmt *) stm;
                    AlterTableCmd *newcmd;

                    if (!rewrite)
                        TryReuseIndex(oldId, stmt);

                    rel = relation_openrv(stmt->relation, lockmode);
                    tab = ATGetQueueEntry(wqueue, rel);
                    newcmd = makeNode(AlterTableCmd);
                    newcmd->subtype = AT_ReAddIndex;
                    newcmd->def = (Node *) stmt;
                    tab->subcmds[AT_PASS_OLD_INDEX] =
                        lappend(tab->subcmds[AT_PASS_OLD_INDEX], newcmd);
                    relation_close(rel, NoLock);
                    break;
                }
            case T_AlterTableStmt:
                {
                    AlterTableStmt *stmt = (AlterTableStmt *) stm;
                    ListCell   *lcmd;

                    rel = relation_openrv(stmt->relation, lockmode);
                    tab = ATGetQueueEntry(wqueue, rel);
                    foreach(lcmd, stmt->cmds)
                    {
                        AlterTableCmd *cmd = (AlterTableCmd *) lfirst(lcmd);
                        Constraint *con;

                        switch (cmd->subtype)
                        {
                            case AT_AddIndex:
                                Assert(IsA(cmd->def, IndexStmt));
                                if (!rewrite)
                                    TryReuseIndex(get_constraint_index(oldId),
                                                  (IndexStmt *) cmd->def);
                                cmd->subtype = AT_ReAddIndex;
                                tab->subcmds[AT_PASS_OLD_INDEX] =
                                    lappend(tab->subcmds[AT_PASS_OLD_INDEX], cmd);
                                break;
                            case AT_AddConstraint:
                                Assert(IsA(cmd->def, Constraint));
                                con = (Constraint *) cmd->def;
                                /* rewriting neither side of a FK */
                                if (con->contype == CONSTR_FOREIGN &&
                                    !rewrite && !tab->rewrite)
                                    TryReuseForeignKey(oldId, con);
                                cmd->subtype = AT_ReAddConstraint;
                                tab->subcmds[AT_PASS_OLD_CONSTR] =
                                    lappend(tab->subcmds[AT_PASS_OLD_CONSTR], cmd);
                                break;
                            default:
                                elog(ERROR, "unexpected statement type: %d",
                                     (int) cmd->subtype);
                        }
                    }
                    relation_close(rel, NoLock);
                    break;
                }
            default:
                elog(ERROR, "unexpected statement type: %d",
                     (int) nodeTag(stm));
        }
    }
}

/*
 * Subroutine for ATPostAlterTypeParse().  Calls out to CheckIndexCompatible()
 * for the real analysis, then mutates the IndexStmt based on that verdict.
 */
static void
TryReuseIndex(Oid oldId, IndexStmt *stmt)
{
    if (CheckIndexCompatible(oldId,
                             stmt->relation,
                             stmt->accessMethod,
                             stmt->indexParams,
                             stmt->excludeOpNames))
    {
        Relation    irel = index_open(oldId, NoLock);

        stmt->oldNode = irel->rd_node.relNode;
        index_close(irel, NoLock);
    }
}

/*
 * Subroutine for ATPostAlterTypeParse().
 *
 * Stash the old P-F equality operator into the Constraint node, for possible
 * use by ATAddForeignKeyConstraint() in determining whether revalidation of
 * this constraint can be skipped.
 */
static void
TryReuseForeignKey(Oid oldId, Constraint *con)
{
    HeapTuple   tup;
    Datum       adatum;
    bool        isNull;
    ArrayType  *arr;
    Oid        *rawarr;
    int         numkeys;
    int         i;

    Assert(con->contype == CONSTR_FOREIGN);
    Assert(con->old_conpfeqop == NIL);  /* already prepared this node */

    tup = SearchSysCache1(CONSTROID, ObjectIdGetDatum(oldId));
    if (!HeapTupleIsValid(tup)) /* should not happen */
        elog(ERROR, "cache lookup failed for constraint %u", oldId);

    adatum = SysCacheGetAttr(CONSTROID, tup,
                             Anum_pg_constraint_conpfeqop, &isNull);
    if (isNull)
        elog(ERROR, "null conpfeqop for constraint %u", oldId);
    arr = DatumGetArrayTypeP(adatum);   /* ensure not toasted */
    numkeys = ARR_DIMS(arr)[0];
    /* test follows the one in ri_FetchConstraintInfo() */
    if (ARR_NDIM(arr) != 1 ||
        ARR_HASNULL(arr) ||
        ARR_ELEMTYPE(arr) != OIDOID)
        elog(ERROR, "conpfeqop is not a 1-D Oid array");
    rawarr = (Oid *) ARR_DATA_PTR(arr);

    /* stash a List of the operator Oids in our Constraint node */
    for (i = 0; i < numkeys; i++)
        con->old_conpfeqop = lcons_oid(rawarr[i], con->old_conpfeqop);

    ReleaseSysCache(tup);
}

/*
 * ALTER TABLE OWNER
 *
 * recursing is true if we are recursing from a table to its indexes,
 * sequences, or toast table.  We don't allow the ownership of those things to
 * be changed separately from the parent table.  Also, we can skip permission
 * checks (this is necessary not just an optimization, else we'd fail to
 * handle toast tables properly).
 *
 * recursing is also true if ALTER TYPE OWNER is calling us to fix up a
 * free-standing composite type.
 */
void
ATExecChangeOwner(Oid relationOid, Oid newOwnerId, bool recursing, LOCKMODE lockmode)
{
    Relation    target_rel;
    Relation    class_rel;
    HeapTuple   tuple;
    Form_pg_class tuple_class;

    /*
     * Get exclusive lock till end of transaction on the target table. Use
     * relation_open so that we can work on indexes and sequences.
     */
    target_rel = relation_open(relationOid, lockmode);

    /* Get its pg_class tuple, too */
    class_rel = heap_open(RelationRelationId, RowExclusiveLock);

    tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relationOid));
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for relation %u", relationOid);
    tuple_class = (Form_pg_class) GETSTRUCT(tuple);

    /* Can we change the ownership of this tuple? */
    switch (tuple_class->relkind)
    {
        case RELKIND_RELATION:
        case RELKIND_VIEW:
        case RELKIND_MATVIEW:
        case RELKIND_FOREIGN_TABLE:
            /* ok to change owner */
            break;
        case RELKIND_INDEX:
            if (!recursing)
            {
                /*
                 * Because ALTER INDEX OWNER used to be allowed, and in fact
                 * is generated by old versions of pg_dump, we give a warning
                 * and do nothing rather than erroring out.  Also, to avoid
                 * unnecessary chatter while restoring those old dumps, say
                 * nothing at all if the command would be a no-op anyway.
                 */
                if (tuple_class->relowner != newOwnerId)
                    ereport(WARNING,
                            (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                             errmsg("cannot change owner of index \"%s\"",
                                    NameStr(tuple_class->relname)),
                             errhint("Change the ownership of the index's table, instead.")));
                /* quick hack to exit via the no-op path */
                newOwnerId = tuple_class->relowner;
            }
            break;
        case RELKIND_SEQUENCE:
            if (!recursing &&
                tuple_class->relowner != newOwnerId)
            {
                /* if it's an owned sequence, disallow changing it by itself */
                Oid         tableId;
                int32       colId;

                if (sequenceIsOwned(relationOid, &tableId, &colId))
                    ereport(ERROR,
                            (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                             errmsg("cannot change owner of sequence \"%s\"",
                                    NameStr(tuple_class->relname)),
                      errdetail("Sequence \"%s\" is linked to table \"%s\".",
                                NameStr(tuple_class->relname),
                                get_rel_name(tableId))));
            }
            break;
        case RELKIND_COMPOSITE_TYPE:
            if (recursing)
                break;
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                     errmsg("\"%s\" is a composite type",
                            NameStr(tuple_class->relname)),
                     errhint("Use ALTER TYPE instead.")));
            break;
        case RELKIND_TOASTVALUE:
            if (recursing)
                break;
            /* FALL THRU */
        default:
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
            errmsg("\"%s\" is not a table, view, sequence, or foreign table",
                   NameStr(tuple_class->relname))));
    }

    /*
     * If the new owner is the same as the existing owner, consider the
     * command to have succeeded.  This is for dump restoration purposes.
     */
    if (tuple_class->relowner != newOwnerId)
    {
        Datum       repl_val[Natts_pg_class];
        bool        repl_null[Natts_pg_class];
        bool        repl_repl[Natts_pg_class];
        Acl        *newAcl;
        Datum       aclDatum;
        bool        isNull;
        HeapTuple   newtuple;

        /* skip permission checks when recursing to index or toast table */
        if (!recursing)
        {
            /* Superusers can always do it */
            if (!superuser())
            {
                Oid         namespaceOid = tuple_class->relnamespace;
                AclResult   aclresult;

                /* Otherwise, must be owner of the existing object */
                if (!pg_class_ownercheck(relationOid, GetUserId()))
                    aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
                                   RelationGetRelationName(target_rel));

                /* Must be able to become new owner */
                check_is_member_of_role(GetUserId(), newOwnerId);

                /* New owner must have CREATE privilege on namespace */
                aclresult = pg_namespace_aclcheck(namespaceOid, newOwnerId,
                                                  ACL_CREATE);
                if (aclresult != ACLCHECK_OK)
                    aclcheck_error(aclresult, ACL_KIND_NAMESPACE,
                                   get_namespace_name(namespaceOid));
            }
        }

        memset(repl_null, false, sizeof(repl_null));
        memset(repl_repl, false, sizeof(repl_repl));

        repl_repl[Anum_pg_class_relowner - 1] = true;
        repl_val[Anum_pg_class_relowner - 1] = ObjectIdGetDatum(newOwnerId);

        /*
         * Determine the modified ACL for the new owner.  This is only
         * necessary when the ACL is non-null.
         */
        aclDatum = SysCacheGetAttr(RELOID, tuple,
                                   Anum_pg_class_relacl,
                                   &isNull);
        if (!isNull)
        {
            newAcl = aclnewowner(DatumGetAclP(aclDatum),
                                 tuple_class->relowner, newOwnerId);
            repl_repl[Anum_pg_class_relacl - 1] = true;
            repl_val[Anum_pg_class_relacl - 1] = PointerGetDatum(newAcl);
        }

        newtuple = heap_modify_tuple(tuple, RelationGetDescr(class_rel), repl_val, repl_null, repl_repl);

        simple_heap_update(class_rel, &newtuple->t_self, newtuple);
        CatalogUpdateIndexes(class_rel, newtuple);

        heap_freetuple(newtuple);

        /*
         * We must similarly update any per-column ACLs to reflect the new
         * owner; for neatness reasons that's split out as a subroutine.
         */
        change_owner_fix_column_acls(relationOid,
                                     tuple_class->relowner,
                                     newOwnerId);

        /*
         * Update owner dependency reference, if any.  A composite type has
         * none, because it's tracked for the pg_type entry instead of here;
         * indexes and TOAST tables don't have their own entries either.
         */
        if (tuple_class->relkind != RELKIND_COMPOSITE_TYPE &&
            tuple_class->relkind != RELKIND_INDEX &&
            tuple_class->relkind != RELKIND_TOASTVALUE)
            changeDependencyOnOwner(RelationRelationId, relationOid,
                                    newOwnerId);

        /*
         * Also change the ownership of the table's row type, if it has one
         */
        if (tuple_class->relkind != RELKIND_INDEX)
            AlterTypeOwnerInternal(tuple_class->reltype, newOwnerId,
                             tuple_class->relkind == RELKIND_COMPOSITE_TYPE);

        /*
         * If we are operating on a table or materialized view, also change
         * the ownership of any indexes and sequences that belong to the
         * relation, as well as its toast table (if it has one).
         */
        if (tuple_class->relkind == RELKIND_RELATION ||
            tuple_class->relkind == RELKIND_MATVIEW ||
            tuple_class->relkind == RELKIND_TOASTVALUE)
        {
            List       *index_oid_list;
            ListCell   *i;

            /* Find all the indexes belonging to this relation */
            index_oid_list = RelationGetIndexList(target_rel);

            /* For each index, recursively change its ownership */
            foreach(i, index_oid_list)
                ATExecChangeOwner(lfirst_oid(i), newOwnerId, true, lockmode);

            list_free(index_oid_list);
        }

        if (tuple_class->relkind == RELKIND_RELATION ||
            tuple_class->relkind == RELKIND_MATVIEW)
        {
            /* If it has a toast table, recurse to change its ownership */
            if (tuple_class->reltoastrelid != InvalidOid)
                ATExecChangeOwner(tuple_class->reltoastrelid, newOwnerId,
                                  true, lockmode);

            /* If it has dependent sequences, recurse to change them too */
            change_owner_recurse_to_sequences(relationOid, newOwnerId, lockmode);
        }
    }

    InvokeObjectPostAlterHook(RelationRelationId, relationOid, 0);

    ReleaseSysCache(tuple);
    heap_close(class_rel, RowExclusiveLock);
    relation_close(target_rel, NoLock);
}

/*
 * change_owner_fix_column_acls
 *
 * Helper function for ATExecChangeOwner.  Scan the columns of the table
 * and fix any non-null column ACLs to reflect the new owner.
 */
static void
change_owner_fix_column_acls(Oid relationOid, Oid oldOwnerId, Oid newOwnerId)
{
    Relation    attRelation;
    SysScanDesc scan;
    ScanKeyData key[1];
    HeapTuple   attributeTuple;

    attRelation = heap_open(AttributeRelationId, RowExclusiveLock);
    ScanKeyInit(&key[0],
                Anum_pg_attribute_attrelid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(relationOid));
    scan = systable_beginscan(attRelation, AttributeRelidNumIndexId,
                              true, SnapshotNow, 1, key);
    while (HeapTupleIsValid(attributeTuple = systable_getnext(scan)))
    {
        Form_pg_attribute att = (Form_pg_attribute) GETSTRUCT(attributeTuple);
        Datum       repl_val[Natts_pg_attribute];
        bool        repl_null[Natts_pg_attribute];
        bool        repl_repl[Natts_pg_attribute];
        Acl        *newAcl;
        Datum       aclDatum;
        bool        isNull;
        HeapTuple   newtuple;

        /* Ignore dropped columns */
        if (att->attisdropped)
            continue;

        aclDatum = heap_getattr(attributeTuple,
                                Anum_pg_attribute_attacl,
                                RelationGetDescr(attRelation),
                                &isNull);
        /* Null ACLs do not require changes */
        if (isNull)
            continue;

        memset(repl_null, false, sizeof(repl_null));
        memset(repl_repl, false, sizeof(repl_repl));

        newAcl = aclnewowner(DatumGetAclP(aclDatum),
                             oldOwnerId, newOwnerId);
        repl_repl[Anum_pg_attribute_attacl - 1] = true;
        repl_val[Anum_pg_attribute_attacl - 1] = PointerGetDatum(newAcl);

        newtuple = heap_modify_tuple(attributeTuple,
                                     RelationGetDescr(attRelation),
                                     repl_val, repl_null, repl_repl);

        simple_heap_update(attRelation, &newtuple->t_self, newtuple);
        CatalogUpdateIndexes(attRelation, newtuple);

        heap_freetuple(newtuple);
    }
    systable_endscan(scan);
    heap_close(attRelation, RowExclusiveLock);
}

/*
 * change_owner_recurse_to_sequences
 *
 * Helper function for ATExecChangeOwner.  Examines pg_depend searching
 * for sequences that are dependent on serial columns, and changes their
 * ownership.
 */
static void
change_owner_recurse_to_sequences(Oid relationOid, Oid newOwnerId, LOCKMODE lockmode)
{
    Relation    depRel;
    SysScanDesc scan;
    ScanKeyData key[2];
    HeapTuple   tup;

    /*
     * SERIAL sequences are those having an auto dependency on one of the
     * table's columns (we don't care *which* column, exactly).
     */
    depRel = heap_open(DependRelationId, AccessShareLock);

    ScanKeyInit(&key[0],
                Anum_pg_depend_refclassid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationRelationId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_refobjid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(relationOid));
    /* we leave refobjsubid unspecified */

    scan = systable_beginscan(depRel, DependReferenceIndexId, true,
                              SnapshotNow, 2, key);

    while (HeapTupleIsValid(tup = systable_getnext(scan)))
    {
        Form_pg_depend depForm = (Form_pg_depend) GETSTRUCT(tup);
        Relation    seqRel;

        /* skip dependencies other than auto dependencies on columns */
        if (depForm->refobjsubid == 0 ||
            depForm->classid != RelationRelationId ||
            depForm->objsubid != 0 ||
            depForm->deptype != DEPENDENCY_AUTO)
            continue;

        /* Use relation_open just in case it's an index */
        seqRel = relation_open(depForm->objid, lockmode);

        /* skip non-sequence relations */
        if (RelationGetForm(seqRel)->relkind != RELKIND_SEQUENCE)
        {
            /* No need to keep the lock */
            relation_close(seqRel, lockmode);
            continue;
        }

        /* We don't need to close the sequence while we alter it. */
        ATExecChangeOwner(depForm->objid, newOwnerId, true, lockmode);

        /* Now we can close it.  Keep the lock till end of transaction. */
        relation_close(seqRel, NoLock);
    }

    systable_endscan(scan);

    relation_close(depRel, AccessShareLock);
}

/*
 * ALTER TABLE CLUSTER ON
 *
 * The only thing we have to do is to change the indisclustered bits.
 */
static void
ATExecClusterOn(Relation rel, const char *indexName, LOCKMODE lockmode)
{
    Oid         indexOid;

    indexOid = get_relname_relid(indexName, rel->rd_rel->relnamespace);

    if (!OidIsValid(indexOid))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("index \"%s\" for table \"%s\" does not exist",
                        indexName, RelationGetRelationName(rel))));

    /* Check index is valid to cluster on */
    check_index_is_clusterable(rel, indexOid, false, lockmode);

    /* And do the work */
    mark_index_clustered(rel, indexOid, false);
}

/*
 * ALTER TABLE SET WITHOUT CLUSTER
 *
 * We have to find any indexes on the table that have indisclustered bit
 * set and turn it off.
 */
static void
ATExecDropCluster(Relation rel, LOCKMODE lockmode)
{
    mark_index_clustered(rel, InvalidOid, false);
}

/*
 * ALTER TABLE SET TABLESPACE
 */
static void
ATPrepSetTableSpace(AlteredTableInfo *tab, Relation rel, char *tablespacename, LOCKMODE lockmode)
{
    Oid         tablespaceId;
    AclResult   aclresult;

    /* Check that the tablespace exists */
    tablespaceId = get_tablespace_oid(tablespacename, false);

    /* Check its permissions */
    aclresult = pg_tablespace_aclcheck(tablespaceId, GetUserId(), ACL_CREATE);
    if (aclresult != ACLCHECK_OK)
        aclcheck_error(aclresult, ACL_KIND_TABLESPACE, tablespacename);

    /* Save info for Phase 3 to do the real work */
    if (OidIsValid(tab->newTableSpace))
        ereport(ERROR,
                (errcode(ERRCODE_SYNTAX_ERROR),
                 errmsg("cannot have multiple SET TABLESPACE subcommands")));
    tab->newTableSpace = tablespaceId;
}

/*
 * Set, reset, or replace reloptions.
 */
static void
ATExecSetRelOptions(Relation rel, List *defList, AlterTableType operation,
                    LOCKMODE lockmode)
{
    Oid         relid;
    Relation    pgclass;
    HeapTuple   tuple;
    HeapTuple   newtuple;
    Datum       datum;
    bool        isnull;
    Datum       newOptions;
    Datum       repl_val[Natts_pg_class];
    bool        repl_null[Natts_pg_class];
    bool        repl_repl[Natts_pg_class];
    static char *validnsps[] = HEAP_RELOPT_NAMESPACES;

    if (defList == NIL && operation != AT_ReplaceRelOptions)
        return;                 /* nothing to do */

    pgclass = heap_open(RelationRelationId, RowExclusiveLock);

    /* Fetch heap tuple */
    relid = RelationGetRelid(rel);
    tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for relation %u", relid);

    if (operation == AT_ReplaceRelOptions)
    {
        /*
         * If we're supposed to replace the reloptions list, we just pretend
         * there were none before.
         */
        datum = (Datum) 0;
        isnull = true;
    }
    else
    {
        /* Get the old reloptions */
        datum = SysCacheGetAttr(RELOID, tuple, Anum_pg_class_reloptions,
                                &isnull);
    }

    /* Generate new proposed reloptions (text array) */
    newOptions = transformRelOptions(isnull ? (Datum) 0 : datum,
                                     defList, NULL, validnsps, false,
                                     operation == AT_ResetRelOptions);

    /* Validate */
    switch (rel->rd_rel->relkind)
    {
        case RELKIND_RELATION:
        case RELKIND_TOASTVALUE:
        case RELKIND_VIEW:
        case RELKIND_MATVIEW:
            (void) heap_reloptions(rel->rd_rel->relkind, newOptions, true);
            break;
        case RELKIND_INDEX:
            (void) index_reloptions(rel->rd_am->amoptions, newOptions, true);
            break;
        default:
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                     errmsg("\"%s\" is not a table, view, materialized view, index, or TOAST table",
                            RelationGetRelationName(rel))));
            break;
    }

    /*
     * All we need do here is update the pg_class row; the new options will be
     * propagated into relcaches during post-commit cache inval.
     */
    memset(repl_val, 0, sizeof(repl_val));
    memset(repl_null, false, sizeof(repl_null));
    memset(repl_repl, false, sizeof(repl_repl));

    if (newOptions != (Datum) 0)
        repl_val[Anum_pg_class_reloptions - 1] = newOptions;
    else
        repl_null[Anum_pg_class_reloptions - 1] = true;

    repl_repl[Anum_pg_class_reloptions - 1] = true;

    newtuple = heap_modify_tuple(tuple, RelationGetDescr(pgclass),
                                 repl_val, repl_null, repl_repl);

    simple_heap_update(pgclass, &newtuple->t_self, newtuple);

    CatalogUpdateIndexes(pgclass, newtuple);

    InvokeObjectPostAlterHook(RelationRelationId, RelationGetRelid(rel), 0);

    heap_freetuple(newtuple);

    ReleaseSysCache(tuple);

    /* repeat the whole exercise for the toast table, if there's one */
    if (OidIsValid(rel->rd_rel->reltoastrelid))
    {
        Relation    toastrel;
        Oid         toastid = rel->rd_rel->reltoastrelid;

        toastrel = heap_open(toastid, lockmode);

        /* Fetch heap tuple */
        tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(toastid));
        if (!HeapTupleIsValid(tuple))
            elog(ERROR, "cache lookup failed for relation %u", toastid);

        if (operation == AT_ReplaceRelOptions)
        {
            /*
             * If we're supposed to replace the reloptions list, we just
             * pretend there were none before.
             */
            datum = (Datum) 0;
            isnull = true;
        }
        else
        {
            /* Get the old reloptions */
            datum = SysCacheGetAttr(RELOID, tuple, Anum_pg_class_reloptions,
                                    &isnull);
        }

        newOptions = transformRelOptions(isnull ? (Datum) 0 : datum,
                                         defList, "toast", validnsps, false,
                                         operation == AT_ResetRelOptions);

        (void) heap_reloptions(RELKIND_TOASTVALUE, newOptions, true);

        memset(repl_val, 0, sizeof(repl_val));
        memset(repl_null, false, sizeof(repl_null));
        memset(repl_repl, false, sizeof(repl_repl));

        if (newOptions != (Datum) 0)
            repl_val[Anum_pg_class_reloptions - 1] = newOptions;
        else
            repl_null[Anum_pg_class_reloptions - 1] = true;

        repl_repl[Anum_pg_class_reloptions - 1] = true;

        newtuple = heap_modify_tuple(tuple, RelationGetDescr(pgclass),
                                     repl_val, repl_null, repl_repl);

        simple_heap_update(pgclass, &newtuple->t_self, newtuple);

        CatalogUpdateIndexes(pgclass, newtuple);

        InvokeObjectPostAlterHookArg(RelationRelationId,
                                     RelationGetRelid(toastrel), 0,
                                     InvalidOid, true);

        heap_freetuple(newtuple);

        ReleaseSysCache(tuple);

        heap_close(toastrel, NoLock);
    }

    heap_close(pgclass, RowExclusiveLock);
}

/*
 * Execute ALTER TABLE SET TABLESPACE for cases where there is no tuple
 * rewriting to be done, so we just want to copy the data as fast as possible.
 */
static void
ATExecSetTableSpace(Oid tableOid, Oid newTableSpace, LOCKMODE lockmode)
{
    Relation    rel;
    Oid         oldTableSpace;
    Oid         reltoastrelid;
    Oid         reltoastidxid;
    Oid         newrelfilenode;
    RelFileNode newrnode;
    SMgrRelation dstrel;
    Relation    pg_class;
    HeapTuple   tuple;
    Form_pg_class rd_rel;
    ForkNumber  forkNum;

    /*
     * Need lock here in case we are recursing to toast table or index
     */
    rel = relation_open(tableOid, lockmode);

    /*
     * No work if no change in tablespace.
     */
    oldTableSpace = rel->rd_rel->reltablespace;
    if (newTableSpace == oldTableSpace ||
        (newTableSpace == MyDatabaseTableSpace && oldTableSpace == 0))
    {
        InvokeObjectPostAlterHook(RelationRelationId,
                                  RelationGetRelid(rel), 0);

        relation_close(rel, NoLock);
        return;
    }

    /*
     * We cannot support moving mapped relations into different tablespaces.
     * (In particular this eliminates all shared catalogs.)
     */
    if (RelationIsMapped(rel))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot move system relation \"%s\"",
                        RelationGetRelationName(rel))));

    /* Can't move a non-shared relation into pg_global */
    if (newTableSpace == GLOBALTABLESPACE_OID)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("only shared relations can be placed in pg_global tablespace")));

    /*
     * Don't allow moving temp tables of other backends ... their local buffer
     * manager is not going to cope.
     */
    if (RELATION_IS_OTHER_TEMP(rel))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot move temporary tables of other sessions")));

    reltoastrelid = rel->rd_rel->reltoastrelid;
    reltoastidxid = rel->rd_rel->reltoastidxid;

    /* Get a modifiable copy of the relation's pg_class row */
    pg_class = heap_open(RelationRelationId, RowExclusiveLock);

    tuple = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(tableOid));
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for relation %u", tableOid);
    rd_rel = (Form_pg_class) GETSTRUCT(tuple);

    /*
     * Since we copy the file directly without looking at the shared buffers,
     * we'd better first flush out any pages of the source relation that are
     * in shared buffers.  We assume no new changes will be made while we are
     * holding exclusive lock on the rel.
     */
    FlushRelationBuffers(rel);

    /*
     * Relfilenodes are not unique across tablespaces, so we need to allocate
     * a new one in the new tablespace.
     */
    newrelfilenode = GetNewRelFileNode(newTableSpace, NULL,
                                       rel->rd_rel->relpersistence);

    /* Open old and new relation */
    newrnode = rel->rd_node;
    newrnode.relNode = newrelfilenode;
    newrnode.spcNode = newTableSpace;
    dstrel = smgropen(newrnode, rel->rd_backend);

    RelationOpenSmgr(rel);

    /*
     * Create and copy all forks of the relation, and schedule unlinking of
     * old physical files.
     *
     * NOTE: any conflict in relfilenode value will be caught in
     * RelationCreateStorage().
     */
    RelationCreateStorage(newrnode, rel->rd_rel->relpersistence);

    /* copy main fork */
    copy_relation_data(rel->rd_smgr, dstrel, MAIN_FORKNUM,
                       rel->rd_rel->relpersistence);

    /* copy those extra forks that exist */
    for (forkNum = MAIN_FORKNUM + 1; forkNum <= MAX_FORKNUM; forkNum++)
    {
        if (smgrexists(rel->rd_smgr, forkNum))
        {
            smgrcreate(dstrel, forkNum, false);
            copy_relation_data(rel->rd_smgr, dstrel, forkNum,
                               rel->rd_rel->relpersistence);
        }
    }

    /* drop old relation, and close new one */
    RelationDropStorage(rel);
    smgrclose(dstrel);

    /* update the pg_class row */
    rd_rel->reltablespace = (newTableSpace == MyDatabaseTableSpace) ? InvalidOid : newTableSpace;
    rd_rel->relfilenode = newrelfilenode;
    simple_heap_update(pg_class, &tuple->t_self, tuple);
    CatalogUpdateIndexes(pg_class, tuple);

    InvokeObjectPostAlterHook(RelationRelationId, RelationGetRelid(rel), 0);

    heap_freetuple(tuple);

    heap_close(pg_class, RowExclusiveLock);

    relation_close(rel, NoLock);

    /* Make sure the reltablespace change is visible */
    CommandCounterIncrement();

    /* Move associated toast relation and/or index, too */
    if (OidIsValid(reltoastrelid))
        ATExecSetTableSpace(reltoastrelid, newTableSpace, lockmode);
    if (OidIsValid(reltoastidxid))
        ATExecSetTableSpace(reltoastidxid, newTableSpace, lockmode);
}

/*
 * Copy data, block by block
 */
static void
copy_relation_data(SMgrRelation src, SMgrRelation dst,
                   ForkNumber forkNum, char relpersistence)
{
    char       *buf;
    Page        page;
    bool        use_wal;
    BlockNumber nblocks;
    BlockNumber blkno;

    /*
     * palloc the buffer so that it's MAXALIGN'd.  If it were just a local
     * char[] array, the compiler might align it on any byte boundary, which
     * can seriously hurt transfer speed to and from the kernel; not to
     * mention possibly making log_newpage's accesses to the page header fail.
     */
    buf = (char *) palloc(BLCKSZ);
    page = (Page) buf;

    /*
     * We need to log the copied data in WAL iff WAL archiving/streaming is
     * enabled AND it's a permanent relation.
     */
    use_wal = XLogIsNeeded() && relpersistence == RELPERSISTENCE_PERMANENT;

    nblocks = smgrnblocks(src, forkNum);

    for (blkno = 0; blkno < nblocks; blkno++)
    {
        /* If we got a cancel signal during the copy of the data, quit */
        CHECK_FOR_INTERRUPTS();

        smgrread(src, forkNum, blkno, buf);

        if (!PageIsVerified(page, blkno))
            ereport(ERROR,
                    (errcode(ERRCODE_DATA_CORRUPTED),
                     errmsg("invalid page in block %u of relation %s",
                            blkno,
                            relpathbackend(src->smgr_rnode.node,
                                           src->smgr_rnode.backend,
                                           forkNum))));

        /* XLOG stuff */
        if (use_wal)
            log_newpage(&dst->smgr_rnode.node, forkNum, blkno, page);

        PageSetChecksumInplace(page, blkno);

        /*
         * Now write the page.  We say isTemp = true even if it's not a temp
         * rel, because there's no need for smgr to schedule an fsync for this
         * write; we'll do it ourselves below.
         */
        smgrextend(dst, forkNum, blkno, buf, true);
    }

    pfree(buf);

    /*
     * If the rel is WAL-logged, must fsync before commit.  We use heap_sync
     * to ensure that the toast table gets fsync'd too.  (For a temp or
     * unlogged rel we don't care since the data will be gone after a crash
     * anyway.)
     *
     * It's obvious that we must do this when not WAL-logging the copy. It's
     * less obvious that we have to do it even if we did WAL-log the copied
     * pages. The reason is that since we're copying outside shared buffers, a
     * CHECKPOINT occurring during the copy has no way to flush the previously
     * written data to disk (indeed it won't know the new rel even exists).  A
     * crash later on would replay WAL from the checkpoint, therefore it
     * wouldn't replay our earlier WAL entries. If we do not fsync those pages
     * here, they might still not be on disk when the crash occurs.
     */
    if (relpersistence == RELPERSISTENCE_PERMANENT)
        smgrimmedsync(dst, forkNum);
}

/*
 * ALTER TABLE ENABLE/DISABLE TRIGGER
 *
 * We just pass this off to trigger.c.
 */
static void
ATExecEnableDisableTrigger(Relation rel, char *trigname,
                        char fires_when, bool skip_system, LOCKMODE lockmode)
{
    EnableDisableTrigger(rel, trigname, fires_when, skip_system);
}

/*
 * ALTER TABLE ENABLE/DISABLE RULE
 *
 * We just pass this off to rewriteDefine.c.
 */
static void
ATExecEnableDisableRule(Relation rel, char *trigname,
                        char fires_when, LOCKMODE lockmode)
{
    EnableDisableRule(rel, trigname, fires_when);
}

/*
 * ALTER TABLE INHERIT
 *
 * Add a parent to the child's parents. This verifies that all the columns and
 * check constraints of the parent appear in the child and that they have the
 * same data types and expressions.
 */
static void
ATPrepAddInherit(Relation child_rel)
{
    if (child_rel->rd_rel->reloftype)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("cannot change inheritance of typed table")));
}

static void
ATExecAddInherit(Relation child_rel, RangeVar *parent, LOCKMODE lockmode)
{
    Relation    parent_rel,
                catalogRelation;
    SysScanDesc scan;
    ScanKeyData key;
    HeapTuple   inheritsTuple;
    int32       inhseqno;
    List       *children;

    /*
     * A self-exclusive lock is needed here.  See the similar case in
     * MergeAttributes() for a full explanation.
     */
    parent_rel = heap_openrv(parent, ShareUpdateExclusiveLock);

    /*
     * Must be owner of both parent and child -- child was checked by
     * ATSimplePermissions call in ATPrepCmd
     */
    ATSimplePermissions(parent_rel, ATT_TABLE);

    /* Permanent rels cannot inherit from temporary ones */
    if (parent_rel->rd_rel->relpersistence == RELPERSISTENCE_TEMP &&
        child_rel->rd_rel->relpersistence != RELPERSISTENCE_TEMP)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("cannot inherit from temporary relation \"%s\"",
                        RelationGetRelationName(parent_rel))));

    /* If parent rel is temp, it must belong to this session */
    if (parent_rel->rd_rel->relpersistence == RELPERSISTENCE_TEMP &&
        !parent_rel->rd_islocaltemp)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("cannot inherit from temporary relation of another session")));

    /* Ditto for the child */
    if (child_rel->rd_rel->relpersistence == RELPERSISTENCE_TEMP &&
        !child_rel->rd_islocaltemp)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("cannot inherit to temporary relation of another session")));

    /*
     * Check for duplicates in the list of parents, and determine the highest
     * inhseqno already present; we'll use the next one for the new parent.
     * (Note: get RowExclusiveLock because we will write pg_inherits below.)
     *
     * Note: we do not reject the case where the child already inherits from
     * the parent indirectly; CREATE TABLE doesn't reject comparable cases.
     */
    catalogRelation = heap_open(InheritsRelationId, RowExclusiveLock);
    ScanKeyInit(&key,
                Anum_pg_inherits_inhrelid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationGetRelid(child_rel)));
    scan = systable_beginscan(catalogRelation, InheritsRelidSeqnoIndexId,
                              true, SnapshotNow, 1, &key);

    /* inhseqno sequences start at 1 */
    inhseqno = 0;
    while (HeapTupleIsValid(inheritsTuple = systable_getnext(scan)))
    {
        Form_pg_inherits inh = (Form_pg_inherits) GETSTRUCT(inheritsTuple);

        if (inh->inhparent == RelationGetRelid(parent_rel))
            ereport(ERROR,
                    (errcode(ERRCODE_DUPLICATE_TABLE),
             errmsg("relation \"%s\" would be inherited from more than once",
                    RelationGetRelationName(parent_rel))));
        if (inh->inhseqno > inhseqno)
            inhseqno = inh->inhseqno;
    }
    systable_endscan(scan);

    /*
     * Prevent circularity by seeing if proposed parent inherits from child.
     * (In particular, this disallows making a rel inherit from itself.)
     *
     * This is not completely bulletproof because of race conditions: in
     * multi-level inheritance trees, someone else could concurrently be
     * making another inheritance link that closes the loop but does not join
     * either of the rels we have locked.  Preventing that seems to require
     * exclusive locks on the entire inheritance tree, which is a cure worse
     * than the disease.  find_all_inheritors() will cope with circularity
     * anyway, so don't sweat it too much.
     *
     * We use weakest lock we can on child's children, namely AccessShareLock.
     */
    children = find_all_inheritors(RelationGetRelid(child_rel),
                                   AccessShareLock, NULL);

    if (list_member_oid(children, RelationGetRelid(parent_rel)))
        ereport(ERROR,
                (errcode(ERRCODE_DUPLICATE_TABLE),
                 errmsg("circular inheritance not allowed"),
                 errdetail("\"%s\" is already a child of \"%s\".",
                           parent->relname,
                           RelationGetRelationName(child_rel))));

    /* If parent has OIDs then child must have OIDs */
    if (parent_rel->rd_rel->relhasoids && !child_rel->rd_rel->relhasoids)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("table \"%s\" without OIDs cannot inherit from table \"%s\" with OIDs",
                        RelationGetRelationName(child_rel),
                        RelationGetRelationName(parent_rel))));

    /* Match up the columns and bump attinhcount as needed */
    MergeAttributesIntoExisting(child_rel, parent_rel);

    /* Match up the constraints and bump coninhcount as needed */
    MergeConstraintsIntoExisting(child_rel, parent_rel);

    /*
     * OK, it looks valid.  Make the catalog entries that show inheritance.
     */
    StoreCatalogInheritance1(RelationGetRelid(child_rel),
                             RelationGetRelid(parent_rel),
                             inhseqno + 1,
                             catalogRelation);

    /* Now we're done with pg_inherits */
    heap_close(catalogRelation, RowExclusiveLock);

    /* keep our lock on the parent relation until commit */
    heap_close(parent_rel, NoLock);
}

/*
 * Obtain the source-text form of the constraint expression for a check
 * constraint, given its pg_constraint tuple
 */
static char *
decompile_conbin(HeapTuple contup, TupleDesc tupdesc)
{
    Form_pg_constraint con;
    bool        isnull;
    Datum       attr;
    Datum       expr;

    con = (Form_pg_constraint) GETSTRUCT(contup);
    attr = heap_getattr(contup, Anum_pg_constraint_conbin, tupdesc, &isnull);
    if (isnull)
        elog(ERROR, "null conbin for constraint %u", HeapTupleGetOid(contup));

    expr = DirectFunctionCall2(pg_get_expr, attr,
                               ObjectIdGetDatum(con->conrelid));
    return TextDatumGetCString(expr);
}

/*
 * Determine whether two check constraints are functionally equivalent
 *
 * The test we apply is to see whether they reverse-compile to the same
 * source string.  This insulates us from issues like whether attributes
 * have the same physical column numbers in parent and child relations.
 */
static bool
constraints_equivalent(HeapTuple a, HeapTuple b, TupleDesc tupleDesc)
{
    Form_pg_constraint acon = (Form_pg_constraint) GETSTRUCT(a);
    Form_pg_constraint bcon = (Form_pg_constraint) GETSTRUCT(b);

    if (acon->condeferrable != bcon->condeferrable ||
        acon->condeferred != bcon->condeferred ||
        strcmp(decompile_conbin(a, tupleDesc),
               decompile_conbin(b, tupleDesc)) != 0)
        return false;
    else
        return true;
}

/*
 * Check columns in child table match up with columns in parent, and increment
 * their attinhcount.
 *
 * Called by ATExecAddInherit
 *
 * Currently all parent columns must be found in child. Missing columns are an
 * error.  One day we might consider creating new columns like CREATE TABLE
 * does.  However, that is widely unpopular --- in the common use case of
 * partitioned tables it's a foot-gun.
 *
 * The data type must match exactly. If the parent column is NOT NULL then
 * the child must be as well. Defaults are not compared, however.
 */
static void
MergeAttributesIntoExisting(Relation child_rel, Relation parent_rel)
{
    Relation    attrrel;
    AttrNumber  parent_attno;
    int         parent_natts;
    TupleDesc   tupleDesc;
    HeapTuple   tuple;

    attrrel = heap_open(AttributeRelationId, RowExclusiveLock);

    tupleDesc = RelationGetDescr(parent_rel);
    parent_natts = tupleDesc->natts;

    for (parent_attno = 1; parent_attno <= parent_natts; parent_attno++)
    {
        Form_pg_attribute attribute = tupleDesc->attrs[parent_attno - 1];
        char       *attributeName = NameStr(attribute->attname);

        /* Ignore dropped columns in the parent. */
        if (attribute->attisdropped)
            continue;

        /* Find same column in child (matching on column name). */
        tuple = SearchSysCacheCopyAttName(RelationGetRelid(child_rel),
                                          attributeName);
        if (HeapTupleIsValid(tuple))
        {
            /* Check they are same type, typmod, and collation */
            Form_pg_attribute childatt = (Form_pg_attribute) GETSTRUCT(tuple);

            if (attribute->atttypid != childatt->atttypid ||
                attribute->atttypmod != childatt->atttypmod)
                ereport(ERROR,
                        (errcode(ERRCODE_DATATYPE_MISMATCH),
                         errmsg("child table \"%s\" has different type for column \"%s\"",
                                RelationGetRelationName(child_rel),
                                attributeName)));

            if (attribute->attcollation != childatt->attcollation)
                ereport(ERROR,
                        (errcode(ERRCODE_COLLATION_MISMATCH),
                         errmsg("child table \"%s\" has different collation for column \"%s\"",
                                RelationGetRelationName(child_rel),
                                attributeName)));

            /*
             * Check child doesn't discard NOT NULL property.  (Other
             * constraints are checked elsewhere.)
             */
            if (attribute->attnotnull && !childatt->attnotnull)
                ereport(ERROR,
                        (errcode(ERRCODE_DATATYPE_MISMATCH),
                errmsg("column \"%s\" in child table must be marked NOT NULL",
                       attributeName)));

            /*
             * OK, bump the child column's inheritance count.  (If we fail
             * later on, this change will just roll back.)
             */
            childatt->attinhcount++;
            simple_heap_update(attrrel, &tuple->t_self, tuple);
            CatalogUpdateIndexes(attrrel, tuple);
            heap_freetuple(tuple);
        }
        else
        {
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
                     errmsg("child table is missing column \"%s\"",
                            attributeName)));
        }
    }

    heap_close(attrrel, RowExclusiveLock);
}

/*
 * Check constraints in child table match up with constraints in parent,
 * and increment their coninhcount.
 *
 * Constraints that are marked ONLY in the parent are ignored.
 *
 * Called by ATExecAddInherit
 *
 * Currently all constraints in parent must be present in the child. One day we
 * may consider adding new constraints like CREATE TABLE does.
 *
 * XXX This is O(N^2) which may be an issue with tables with hundreds of
 * constraints. As long as tables have more like 10 constraints it shouldn't be
 * a problem though. Even 100 constraints ought not be the end of the world.
 *
 * XXX See MergeWithExistingConstraint too if you change this code.
 */
static void
MergeConstraintsIntoExisting(Relation child_rel, Relation parent_rel)
{
    Relation    catalog_relation;
    TupleDesc   tuple_desc;
    SysScanDesc parent_scan;
    ScanKeyData parent_key;
    HeapTuple   parent_tuple;

    catalog_relation = heap_open(ConstraintRelationId, RowExclusiveLock);
    tuple_desc = RelationGetDescr(catalog_relation);

    /* Outer loop scans through the parent's constraint definitions */
    ScanKeyInit(&parent_key,
                Anum_pg_constraint_conrelid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationGetRelid(parent_rel)));
    parent_scan = systable_beginscan(catalog_relation, ConstraintRelidIndexId,
                                     true, SnapshotNow, 1, &parent_key);

    while (HeapTupleIsValid(parent_tuple = systable_getnext(parent_scan)))
    {
        Form_pg_constraint parent_con = (Form_pg_constraint) GETSTRUCT(parent_tuple);
        SysScanDesc child_scan;
        ScanKeyData child_key;
        HeapTuple   child_tuple;
        bool        found = false;

        if (parent_con->contype != CONSTRAINT_CHECK)
            continue;

        /* if the parent's constraint is marked NO INHERIT, it's not inherited */
        if (parent_con->connoinherit)
            continue;

        /* Search for a child constraint matching this one */
        ScanKeyInit(&child_key,
                    Anum_pg_constraint_conrelid,
                    BTEqualStrategyNumber, F_OIDEQ,
                    ObjectIdGetDatum(RelationGetRelid(child_rel)));
        child_scan = systable_beginscan(catalog_relation, ConstraintRelidIndexId,
                                        true, SnapshotNow, 1, &child_key);

        while (HeapTupleIsValid(child_tuple = systable_getnext(child_scan)))
        {
            Form_pg_constraint child_con = (Form_pg_constraint) GETSTRUCT(child_tuple);
            HeapTuple   child_copy;

            if (child_con->contype != CONSTRAINT_CHECK)
                continue;

            if (strcmp(NameStr(parent_con->conname),
                       NameStr(child_con->conname)) != 0)
                continue;

            if (!constraints_equivalent(parent_tuple, child_tuple, tuple_desc))
                ereport(ERROR,
                        (errcode(ERRCODE_DATATYPE_MISMATCH),
                         errmsg("child table \"%s\" has different definition for check constraint \"%s\"",
                                RelationGetRelationName(child_rel),
                                NameStr(parent_con->conname))));

            /* If the constraint is "no inherit" then cannot merge */
            if (child_con->connoinherit)
                ereport(ERROR,
                        (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                         errmsg("constraint \"%s\" conflicts with non-inherited constraint on child table \"%s\"",
                                NameStr(child_con->conname),
                                RelationGetRelationName(child_rel))));

            /*
             * OK, bump the child constraint's inheritance count.  (If we fail
             * later on, this change will just roll back.)
             */
            child_copy = heap_copytuple(child_tuple);
            child_con = (Form_pg_constraint) GETSTRUCT(child_copy);
            child_con->coninhcount++;
            simple_heap_update(catalog_relation, &child_copy->t_self, child_copy);
            CatalogUpdateIndexes(catalog_relation, child_copy);
            heap_freetuple(child_copy);

            found = true;
            break;
        }

        systable_endscan(child_scan);

        if (!found)
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
                     errmsg("child table is missing constraint \"%s\"",
                            NameStr(parent_con->conname))));
    }

    systable_endscan(parent_scan);
    heap_close(catalog_relation, RowExclusiveLock);
}

/*
 * ALTER TABLE NO INHERIT
 *
 * Drop a parent from the child's parents. This just adjusts the attinhcount
 * and attislocal of the columns and removes the pg_inherit and pg_depend
 * entries.
 *
 * If attinhcount goes to 0 then attislocal gets set to true. If it goes back
 * up attislocal stays true, which means if a child is ever removed from a
 * parent then its columns will never be automatically dropped which may
 * surprise. But at least we'll never surprise by dropping columns someone
 * isn't expecting to be dropped which would actually mean data loss.
 *
 * coninhcount and conislocal for inherited constraints are adjusted in
 * exactly the same way.
 */
static void
ATExecDropInherit(Relation rel, RangeVar *parent, LOCKMODE lockmode)
{
    Relation    parent_rel;
    Relation    catalogRelation;
    SysScanDesc scan;
    ScanKeyData key[3];
    HeapTuple   inheritsTuple,
                attributeTuple,
                constraintTuple;
    List       *connames;
    bool        found = false;

    /*
     * AccessShareLock on the parent is probably enough, seeing that DROP
     * TABLE doesn't lock parent tables at all.  We need some lock since we'll
     * be inspecting the parent's schema.
     */
    parent_rel = heap_openrv(parent, AccessShareLock);

    /*
     * We don't bother to check ownership of the parent table --- ownership of
     * the child is presumed enough rights.
     */

    /*
     * Find and destroy the pg_inherits entry linking the two, or error out if
     * there is none.
     */
    catalogRelation = heap_open(InheritsRelationId, RowExclusiveLock);
    ScanKeyInit(&key[0],
                Anum_pg_inherits_inhrelid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationGetRelid(rel)));
    scan = systable_beginscan(catalogRelation, InheritsRelidSeqnoIndexId,
                              true, SnapshotNow, 1, key);

    while (HeapTupleIsValid(inheritsTuple = systable_getnext(scan)))
    {
        Oid         inhparent;

        inhparent = ((Form_pg_inherits) GETSTRUCT(inheritsTuple))->inhparent;
        if (inhparent == RelationGetRelid(parent_rel))
        {
            simple_heap_delete(catalogRelation, &inheritsTuple->t_self);
            found = true;
            break;
        }
    }

    systable_endscan(scan);
    heap_close(catalogRelation, RowExclusiveLock);

    if (!found)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_TABLE),
                 errmsg("relation \"%s\" is not a parent of relation \"%s\"",
                        RelationGetRelationName(parent_rel),
                        RelationGetRelationName(rel))));

    /*
     * Search through child columns looking for ones matching parent rel
     */
    catalogRelation = heap_open(AttributeRelationId, RowExclusiveLock);
    ScanKeyInit(&key[0],
                Anum_pg_attribute_attrelid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationGetRelid(rel)));
    scan = systable_beginscan(catalogRelation, AttributeRelidNumIndexId,
                              true, SnapshotNow, 1, key);
    while (HeapTupleIsValid(attributeTuple = systable_getnext(scan)))
    {
        Form_pg_attribute att = (Form_pg_attribute) GETSTRUCT(attributeTuple);

        /* Ignore if dropped or not inherited */
        if (att->attisdropped)
            continue;
        if (att->attinhcount <= 0)
            continue;

        if (SearchSysCacheExistsAttName(RelationGetRelid(parent_rel),
                                        NameStr(att->attname)))
        {
            /* Decrement inhcount and possibly set islocal to true */
            HeapTuple   copyTuple = heap_copytuple(attributeTuple);
            Form_pg_attribute copy_att = (Form_pg_attribute) GETSTRUCT(copyTuple);

            copy_att->attinhcount--;
            if (copy_att->attinhcount == 0)
                copy_att->attislocal = true;

            simple_heap_update(catalogRelation, &copyTuple->t_self, copyTuple);
            CatalogUpdateIndexes(catalogRelation, copyTuple);
            heap_freetuple(copyTuple);
        }
    }
    systable_endscan(scan);
    heap_close(catalogRelation, RowExclusiveLock);

    /*
     * Likewise, find inherited check constraints and disinherit them. To do
     * this, we first need a list of the names of the parent's check
     * constraints.  (We cheat a bit by only checking for name matches,
     * assuming that the expressions will match.)
     */
    catalogRelation = heap_open(ConstraintRelationId, RowExclusiveLock);
    ScanKeyInit(&key[0],
                Anum_pg_constraint_conrelid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationGetRelid(parent_rel)));
    scan = systable_beginscan(catalogRelation, ConstraintRelidIndexId,
                              true, SnapshotNow, 1, key);

    connames = NIL;

    while (HeapTupleIsValid(constraintTuple = systable_getnext(scan)))
    {
        Form_pg_constraint con = (Form_pg_constraint) GETSTRUCT(constraintTuple);

        if (con->contype == CONSTRAINT_CHECK)
            connames = lappend(connames, pstrdup(NameStr(con->conname)));
    }

    systable_endscan(scan);

    /* Now scan the child's constraints */
    ScanKeyInit(&key[0],
                Anum_pg_constraint_conrelid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationGetRelid(rel)));
    scan = systable_beginscan(catalogRelation, ConstraintRelidIndexId,
                              true, SnapshotNow, 1, key);

    while (HeapTupleIsValid(constraintTuple = systable_getnext(scan)))
    {
        Form_pg_constraint con = (Form_pg_constraint) GETSTRUCT(constraintTuple);
        bool        match;
        ListCell   *lc;

        if (con->contype != CONSTRAINT_CHECK)
            continue;

        match = false;
        foreach(lc, connames)
        {
            if (strcmp(NameStr(con->conname), (char *) lfirst(lc)) == 0)
            {
                match = true;
                break;
            }
        }

        if (match)
        {
            /* Decrement inhcount and possibly set islocal to true */
            HeapTuple   copyTuple = heap_copytuple(constraintTuple);
            Form_pg_constraint copy_con = (Form_pg_constraint) GETSTRUCT(copyTuple);

            if (copy_con->coninhcount <= 0)     /* shouldn't happen */
                elog(ERROR, "relation %u has non-inherited constraint \"%s\"",
                     RelationGetRelid(rel), NameStr(copy_con->conname));

            copy_con->coninhcount--;
            if (copy_con->coninhcount == 0)
                copy_con->conislocal = true;

            simple_heap_update(catalogRelation, &copyTuple->t_self, copyTuple);
            CatalogUpdateIndexes(catalogRelation, copyTuple);
            heap_freetuple(copyTuple);
        }
    }

    systable_endscan(scan);
    heap_close(catalogRelation, RowExclusiveLock);

    drop_parent_dependency(RelationGetRelid(rel),
                           RelationRelationId,
                           RelationGetRelid(parent_rel));

    /*
     * Post alter hook of this inherits. Since object_access_hook doesn't
     * take multiple object identifiers, we relay oid of parent relation
     * using auxiliary_id argument.
     */
    InvokeObjectPostAlterHookArg(InheritsRelationId,
                                 RelationGetRelid(rel), 0,
                                 RelationGetRelid(parent_rel), false);

    /* keep our lock on the parent relation until commit */
    heap_close(parent_rel, NoLock);
}

/*
 * Drop the dependency created by StoreCatalogInheritance1 (CREATE TABLE
 * INHERITS/ALTER TABLE INHERIT -- refclassid will be RelationRelationId) or
 * heap_create_with_catalog (CREATE TABLE OF/ALTER TABLE OF -- refclassid will
 * be TypeRelationId).  There's no convenient way to do this, so go trawling
 * through pg_depend.
 */
static void
drop_parent_dependency(Oid relid, Oid refclassid, Oid refobjid)
{
    Relation    catalogRelation;
    SysScanDesc scan;
    ScanKeyData key[3];
    HeapTuple   depTuple;

    catalogRelation = heap_open(DependRelationId, RowExclusiveLock);

    ScanKeyInit(&key[0],
                Anum_pg_depend_classid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationRelationId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_objid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(relid));
    ScanKeyInit(&key[2],
                Anum_pg_depend_objsubid,
                BTEqualStrategyNumber, F_INT4EQ,
                Int32GetDatum(0));

    scan = systable_beginscan(catalogRelation, DependDependerIndexId, true,
                              SnapshotNow, 3, key);

    while (HeapTupleIsValid(depTuple = systable_getnext(scan)))
    {
        Form_pg_depend dep = (Form_pg_depend) GETSTRUCT(depTuple);

        if (dep->refclassid == refclassid &&
            dep->refobjid == refobjid &&
            dep->refobjsubid == 0 &&
            dep->deptype == DEPENDENCY_NORMAL)
            simple_heap_delete(catalogRelation, &depTuple->t_self);
    }

    systable_endscan(scan);
    heap_close(catalogRelation, RowExclusiveLock);
}

/*
 * ALTER TABLE OF
 *
 * Attach a table to a composite type, as though it had been created with CREATE
 * TABLE OF.  All attname, atttypid, atttypmod and attcollation must match.  The
 * subject table must not have inheritance parents.  These restrictions ensure
 * that you cannot create a configuration impossible with CREATE TABLE OF alone.
 */
static void
ATExecAddOf(Relation rel, const TypeName *ofTypename, LOCKMODE lockmode)
{
    Oid         relid = RelationGetRelid(rel);
    Type        typetuple;
    Oid         typeid;
    Relation    inheritsRelation,
                relationRelation;
    SysScanDesc scan;
    ScanKeyData key;
    AttrNumber  table_attno,
                type_attno;
    TupleDesc   typeTupleDesc,
                tableTupleDesc;
    ObjectAddress tableobj,
                typeobj;
    HeapTuple   classtuple;

    /* Validate the type. */
    typetuple = typenameType(NULL, ofTypename, NULL);
    check_of_type(typetuple);
    typeid = HeapTupleGetOid(typetuple);

    /* Fail if the table has any inheritance parents. */
    inheritsRelation = heap_open(InheritsRelationId, AccessShareLock);
    ScanKeyInit(&key,
                Anum_pg_inherits_inhrelid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(relid));
    scan = systable_beginscan(inheritsRelation, InheritsRelidSeqnoIndexId,
                              true, SnapshotNow, 1, &key);
    if (HeapTupleIsValid(systable_getnext(scan)))
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("typed tables cannot inherit")));
    systable_endscan(scan);
    heap_close(inheritsRelation, AccessShareLock);

    /*
     * Check the tuple descriptors for compatibility.  Unlike inheritance, we
     * require that the order also match.  However, attnotnull need not match.
     * Also unlike inheritance, we do not require matching relhasoids.
     */
    typeTupleDesc = lookup_rowtype_tupdesc(typeid, -1);
    tableTupleDesc = RelationGetDescr(rel);
    table_attno = 1;
    for (type_attno = 1; type_attno <= typeTupleDesc->natts; type_attno++)
    {
        Form_pg_attribute type_attr,
                    table_attr;
        const char *type_attname,
                   *table_attname;

        /* Get the next non-dropped type attribute. */
        type_attr = typeTupleDesc->attrs[type_attno - 1];
        if (type_attr->attisdropped)
            continue;
        type_attname = NameStr(type_attr->attname);

        /* Get the next non-dropped table attribute. */
        do
        {
            if (table_attno > tableTupleDesc->natts)
                ereport(ERROR,
                        (errcode(ERRCODE_DATATYPE_MISMATCH),
                         errmsg("table is missing column \"%s\"",
                                type_attname)));
            table_attr = tableTupleDesc->attrs[table_attno++ - 1];
        } while (table_attr->attisdropped);
        table_attname = NameStr(table_attr->attname);

        /* Compare name. */
        if (strncmp(table_attname, type_attname, NAMEDATALEN) != 0)
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
                 errmsg("table has column \"%s\" where type requires \"%s\"",
                        table_attname, type_attname)));

        /* Compare type. */
        if (table_attr->atttypid != type_attr->atttypid ||
            table_attr->atttypmod != type_attr->atttypmod ||
            table_attr->attcollation != type_attr->attcollation)
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
                  errmsg("table \"%s\" has different type for column \"%s\"",
                         RelationGetRelationName(rel), type_attname)));
    }
    DecrTupleDescRefCount(typeTupleDesc);

    /* Any remaining columns at the end of the table had better be dropped. */
    for (; table_attno <= tableTupleDesc->natts; table_attno++)
    {
        Form_pg_attribute table_attr = tableTupleDesc->attrs[table_attno - 1];

        if (!table_attr->attisdropped)
            ereport(ERROR,
                    (errcode(ERRCODE_DATATYPE_MISMATCH),
                     errmsg("table has extra column \"%s\"",
                            NameStr(table_attr->attname))));
    }

    /* If the table was already typed, drop the existing dependency. */
    if (rel->rd_rel->reloftype)
        drop_parent_dependency(relid, TypeRelationId, rel->rd_rel->reloftype);

    /* Record a dependency on the new type. */
    tableobj.classId = RelationRelationId;
    tableobj.objectId = relid;
    tableobj.objectSubId = 0;
    typeobj.classId = TypeRelationId;
    typeobj.objectId = typeid;
    typeobj.objectSubId = 0;
    recordDependencyOn(&tableobj, &typeobj, DEPENDENCY_NORMAL);

    /* Update pg_class.reloftype */
    relationRelation = heap_open(RelationRelationId, RowExclusiveLock);
    classtuple = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(relid));
    if (!HeapTupleIsValid(classtuple))
        elog(ERROR, "cache lookup failed for relation %u", relid);
    ((Form_pg_class) GETSTRUCT(classtuple))->reloftype = typeid;
    simple_heap_update(relationRelation, &classtuple->t_self, classtuple);
    CatalogUpdateIndexes(relationRelation, classtuple);

    InvokeObjectPostAlterHook(RelationRelationId, relid, 0);

    heap_freetuple(classtuple);
    heap_close(relationRelation, RowExclusiveLock);

    ReleaseSysCache(typetuple);
}

/*
 * ALTER TABLE NOT OF
 *
 * Detach a typed table from its originating type.  Just clear reloftype and
 * remove the dependency.
 */
static void
ATExecDropOf(Relation rel, LOCKMODE lockmode)
{
    Oid         relid = RelationGetRelid(rel);
    Relation    relationRelation;
    HeapTuple   tuple;

    if (!OidIsValid(rel->rd_rel->reloftype))
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not a typed table",
                        RelationGetRelationName(rel))));

    /*
     * We don't bother to check ownership of the type --- ownership of the
     * table is presumed enough rights.  No lock required on the type, either.
     */

    drop_parent_dependency(relid, TypeRelationId, rel->rd_rel->reloftype);

    /* Clear pg_class.reloftype */
    relationRelation = heap_open(RelationRelationId, RowExclusiveLock);
    tuple = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(relid));
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for relation %u", relid);
    ((Form_pg_class) GETSTRUCT(tuple))->reloftype = InvalidOid;
    simple_heap_update(relationRelation, &tuple->t_self, tuple);
    CatalogUpdateIndexes(relationRelation, tuple);

    InvokeObjectPostAlterHook(RelationRelationId, relid, 0);

    heap_freetuple(tuple);
    heap_close(relationRelation, RowExclusiveLock);
}

/*
 * ALTER FOREIGN TABLE <name> OPTIONS (...)
 */
static void
ATExecGenericOptions(Relation rel, List *options)
{
    Relation    ftrel;
    ForeignServer *server;
    ForeignDataWrapper *fdw;
    HeapTuple   tuple;
    bool        isnull;
    Datum       repl_val[Natts_pg_foreign_table];
    bool        repl_null[Natts_pg_foreign_table];
    bool        repl_repl[Natts_pg_foreign_table];
    Datum       datum;
    Form_pg_foreign_table tableform;

    if (options == NIL)
        return;

    ftrel = heap_open(ForeignTableRelationId, RowExclusiveLock);

    tuple = SearchSysCacheCopy1(FOREIGNTABLEREL, rel->rd_id);
    if (!HeapTupleIsValid(tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("foreign table \"%s\" does not exist",
                        RelationGetRelationName(rel))));
    tableform = (Form_pg_foreign_table) GETSTRUCT(tuple);
    server = GetForeignServer(tableform->ftserver);
    fdw = GetForeignDataWrapper(server->fdwid);

    memset(repl_val, 0, sizeof(repl_val));
    memset(repl_null, false, sizeof(repl_null));
    memset(repl_repl, false, sizeof(repl_repl));

    /* Extract the current options */
    datum = SysCacheGetAttr(FOREIGNTABLEREL,
                            tuple,
                            Anum_pg_foreign_table_ftoptions,
                            &isnull);
    if (isnull)
        datum = PointerGetDatum(NULL);

    /* Transform the options */
    datum = transformGenericOptions(ForeignTableRelationId,
                                    datum,
                                    options,
                                    fdw->fdwvalidator);

    if (PointerIsValid(DatumGetPointer(datum)))
        repl_val[Anum_pg_foreign_table_ftoptions - 1] = datum;
    else
        repl_null[Anum_pg_foreign_table_ftoptions - 1] = true;

    repl_repl[Anum_pg_foreign_table_ftoptions - 1] = true;

    /* Everything looks good - update the tuple */

    tuple = heap_modify_tuple(tuple, RelationGetDescr(ftrel),
                              repl_val, repl_null, repl_repl);

    simple_heap_update(ftrel, &tuple->t_self, tuple);
    CatalogUpdateIndexes(ftrel, tuple);

    InvokeObjectPostAlterHook(ForeignTableRelationId,
                              RelationGetRelid(rel), 0);

    heap_close(ftrel, RowExclusiveLock);

    heap_freetuple(tuple);
}

/*
 * Execute ALTER TABLE SET SCHEMA
 */
Oid
AlterTableNamespace(AlterObjectSchemaStmt *stmt)
{
    Relation    rel;
    Oid         relid;
    Oid         oldNspOid;
    Oid         nspOid;
    RangeVar   *newrv;
    ObjectAddresses *objsMoved;

    relid = RangeVarGetRelidExtended(stmt->relation, AccessExclusiveLock,
                                     stmt->missing_ok, false,
                                     RangeVarCallbackForAlterRelation,
                                     (void *) stmt);

    if (!OidIsValid(relid))
    {
        ereport(NOTICE,
                (errmsg("relation \"%s\" does not exist, skipping",
                        stmt->relation->relname)));
        return InvalidOid;
    }

    rel = relation_open(relid, NoLock);

    oldNspOid = RelationGetNamespace(rel);

    /* If it's an owned sequence, disallow moving it by itself. */
    if (rel->rd_rel->relkind == RELKIND_SEQUENCE)
    {
        Oid         tableId;
        int32       colId;

        if (sequenceIsOwned(relid, &tableId, &colId))
            ereport(ERROR,
                    (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot move an owned sequence into another schema"),
                     errdetail("Sequence \"%s\" is linked to table \"%s\".",
                               RelationGetRelationName(rel),
                               get_rel_name(tableId))));
    }

    /* Get and lock schema OID and check its permissions. */
    newrv = makeRangeVar(stmt->newschema, RelationGetRelationName(rel), -1);
    nspOid = RangeVarGetAndCheckCreationNamespace(newrv, NoLock, NULL);

    /* common checks on switching namespaces */
    CheckSetNamespace(oldNspOid, nspOid, RelationRelationId, relid);

    objsMoved = new_object_addresses();
    AlterTableNamespaceInternal(rel, oldNspOid, nspOid, objsMoved);
    free_object_addresses(objsMoved);

    /* close rel, but keep lock until commit */
    relation_close(rel, NoLock);

    return relid;
}

/*
 * The guts of relocating a table or materialized view to another namespace:
 * besides moving the relation itself, its dependent objects are relocated to
 * the new schema.
 */
void
AlterTableNamespaceInternal(Relation rel, Oid oldNspOid, Oid nspOid,
                            ObjectAddresses *objsMoved)
{
    Relation    classRel;

    Assert(objsMoved != NULL);

    /* OK, modify the pg_class row and pg_depend entry */
    classRel = heap_open(RelationRelationId, RowExclusiveLock);

    AlterRelationNamespaceInternal(classRel, RelationGetRelid(rel), oldNspOid,
                                   nspOid, true, objsMoved);

    /* Fix the table's row type too */
    AlterTypeNamespaceInternal(rel->rd_rel->reltype,
                               nspOid, false, false, objsMoved);

    /* Fix other dependent stuff */
    if (rel->rd_rel->relkind == RELKIND_RELATION ||
        rel->rd_rel->relkind == RELKIND_MATVIEW)
    {
        AlterIndexNamespaces(classRel, rel, oldNspOid, nspOid, objsMoved);
        AlterSeqNamespaces(classRel, rel, oldNspOid, nspOid,
                           objsMoved, AccessExclusiveLock);
        AlterConstraintNamespaces(RelationGetRelid(rel), oldNspOid, nspOid,
                                  false, objsMoved);
    }

    heap_close(classRel, RowExclusiveLock);
}

/*
 * The guts of relocating a relation to another namespace: fix the pg_class
 * entry, and the pg_depend entry if any.  Caller must already have
 * opened and write-locked pg_class.
 */
void
AlterRelationNamespaceInternal(Relation classRel, Oid relOid,
                               Oid oldNspOid, Oid newNspOid,
                               bool hasDependEntry, ObjectAddresses *objsMoved)
{
    HeapTuple   classTup;
    Form_pg_class classForm;
    ObjectAddress   thisobj;

    classTup = SearchSysCacheCopy1(RELOID, ObjectIdGetDatum(relOid));
    if (!HeapTupleIsValid(classTup))
        elog(ERROR, "cache lookup failed for relation %u", relOid);
    classForm = (Form_pg_class) GETSTRUCT(classTup);

    Assert(classForm->relnamespace == oldNspOid);

    thisobj.classId = RelationRelationId;
    thisobj.objectId = relOid;
    thisobj.objectSubId = 0;

    /*
     * Do nothing when there's nothing to do.
     */
    if (!object_address_present(&thisobj, objsMoved))
    {
        /* check for duplicate name (more friendly than unique-index failure) */
        if (get_relname_relid(NameStr(classForm->relname),
                              newNspOid) != InvalidOid)
            ereport(ERROR,
                    (errcode(ERRCODE_DUPLICATE_TABLE),
                     errmsg("relation \"%s\" already exists in schema \"%s\"",
                            NameStr(classForm->relname),
                            get_namespace_name(newNspOid))));

        /* classTup is a copy, so OK to scribble on */
        classForm->relnamespace = newNspOid;

        simple_heap_update(classRel, &classTup->t_self, classTup);
        CatalogUpdateIndexes(classRel, classTup);

        /* Update dependency on schema if caller said so */
        if (hasDependEntry &&
            changeDependencyFor(RelationRelationId, relOid,
                                NamespaceRelationId, oldNspOid, newNspOid) != 1)
            elog(ERROR, "failed to change schema dependency for relation \"%s\"",
                 NameStr(classForm->relname));

        add_exact_object_address(&thisobj, objsMoved);

        InvokeObjectPostAlterHook(RelationRelationId, relOid, 0);
    }

    heap_freetuple(classTup);
}

/*
 * Move all indexes for the specified relation to another namespace.
 *
 * Note: we assume adequate permission checking was done by the caller,
 * and that the caller has a suitable lock on the owning relation.
 */
static void
AlterIndexNamespaces(Relation classRel, Relation rel,
                     Oid oldNspOid, Oid newNspOid, ObjectAddresses *objsMoved)
{
    List       *indexList;
    ListCell   *l;

    indexList = RelationGetIndexList(rel);

    foreach(l, indexList)
    {
        Oid         indexOid = lfirst_oid(l);
        ObjectAddress thisobj;

        thisobj.classId = RelationRelationId;
        thisobj.objectId = indexOid;
        thisobj.objectSubId = 0;

        /*
         * Note: currently, the index will not have its own dependency on the
         * namespace, so we don't need to do changeDependencyFor(). There's no
         * row type in pg_type, either.
         *
         * XXX this objsMoved test may be pointless -- surely we have a single
         * dependency link from a relation to each index?
         */
        if (!object_address_present(&thisobj, objsMoved))
        {
            AlterRelationNamespaceInternal(classRel, indexOid,
                                           oldNspOid, newNspOid,
                                           false, objsMoved);
            add_exact_object_address(&thisobj, objsMoved);
        }
    }

    list_free(indexList);
}

/*
 * Move all SERIAL-column sequences of the specified relation to another
 * namespace.
 *
 * Note: we assume adequate permission checking was done by the caller,
 * and that the caller has a suitable lock on the owning relation.
 */
static void
AlterSeqNamespaces(Relation classRel, Relation rel,
                   Oid oldNspOid, Oid newNspOid, ObjectAddresses *objsMoved,
                   LOCKMODE lockmode)
{
    Relation    depRel;
    SysScanDesc scan;
    ScanKeyData key[2];
    HeapTuple   tup;

    /*
     * SERIAL sequences are those having an auto dependency on one of the
     * table's columns (we don't care *which* column, exactly).
     */
    depRel = heap_open(DependRelationId, AccessShareLock);

    ScanKeyInit(&key[0],
                Anum_pg_depend_refclassid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationRelationId));
    ScanKeyInit(&key[1],
                Anum_pg_depend_refobjid,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(RelationGetRelid(rel)));
    /* we leave refobjsubid unspecified */

    scan = systable_beginscan(depRel, DependReferenceIndexId, true,
                              SnapshotNow, 2, key);

    while (HeapTupleIsValid(tup = systable_getnext(scan)))
    {
        Form_pg_depend depForm = (Form_pg_depend) GETSTRUCT(tup);
        Relation    seqRel;

        /* skip dependencies other than auto dependencies on columns */
        if (depForm->refobjsubid == 0 ||
            depForm->classid != RelationRelationId ||
            depForm->objsubid != 0 ||
            depForm->deptype != DEPENDENCY_AUTO)
            continue;

        /* Use relation_open just in case it's an index */
        seqRel = relation_open(depForm->objid, lockmode);

        /* skip non-sequence relations */
        if (RelationGetForm(seqRel)->relkind != RELKIND_SEQUENCE)
        {
            /* No need to keep the lock */
            relation_close(seqRel, lockmode);
            continue;
        }

        /* Fix the pg_class and pg_depend entries */
        AlterRelationNamespaceInternal(classRel, depForm->objid,
                                       oldNspOid, newNspOid,
                                       true, objsMoved);

        /*
         * Sequences have entries in pg_type. We need to be careful to move
         * them to the new namespace, too.
         */
        AlterTypeNamespaceInternal(RelationGetForm(seqRel)->reltype,
                                   newNspOid, false, false, objsMoved);

        /* Now we can close it.  Keep the lock till end of transaction. */
        relation_close(seqRel, NoLock);
    }

    systable_endscan(scan);

    relation_close(depRel, AccessShareLock);
}


/*
 * This code supports
 *  CREATE TEMP TABLE ... ON COMMIT { DROP | PRESERVE ROWS | DELETE ROWS }
 *
 * Because we only support this for TEMP tables, it's sufficient to remember
 * the state in a backend-local data structure.
 */

/*
 * Register a newly-created relation's ON COMMIT action.
 */
void
register_on_commit_action(Oid relid, OnCommitAction action)
{
    OnCommitItem *oc;
    MemoryContext oldcxt;

    /*
     * We needn't bother registering the relation unless there is an ON COMMIT
     * action we need to take.
     */
    if (action == ONCOMMIT_NOOP || action == ONCOMMIT_PRESERVE_ROWS)
        return;

    oldcxt = MemoryContextSwitchTo(CacheMemoryContext);

    oc = (OnCommitItem *) palloc(sizeof(OnCommitItem));
    oc->relid = relid;
    oc->oncommit = action;
    oc->creating_subid = GetCurrentSubTransactionId();
    oc->deleting_subid = InvalidSubTransactionId;

    on_commits = lcons(oc, on_commits);

    MemoryContextSwitchTo(oldcxt);
}

/*
 * Unregister any ON COMMIT action when a relation is deleted.
 *
 * Actually, we only mark the OnCommitItem entry as to be deleted after commit.
 */
void
remove_on_commit_action(Oid relid)
{
    ListCell   *l;

    foreach(l, on_commits)
    {
        OnCommitItem *oc = (OnCommitItem *) lfirst(l);

        if (oc->relid == relid)
        {
            oc->deleting_subid = GetCurrentSubTransactionId();
            break;
        }
    }
}

/*
 * Perform ON COMMIT actions.
 *
 * This is invoked just before actually committing, since it's possible
 * to encounter errors.
 */
void
PreCommit_on_commit_actions(void)
{
    ListCell   *l;
    List       *oids_to_truncate = NIL;

    foreach(l, on_commits)
    {
        OnCommitItem *oc = (OnCommitItem *) lfirst(l);

        /* Ignore entry if already dropped in this xact */
        if (oc->deleting_subid != InvalidSubTransactionId)
            continue;

        switch (oc->oncommit)
        {
            case ONCOMMIT_NOOP:
            case ONCOMMIT_PRESERVE_ROWS:
                /* Do nothing (there shouldn't be such entries, actually) */
                break;
            case ONCOMMIT_DELETE_ROWS:
                /*
                 * If this transaction hasn't accessed any temporary
                 * relations, we can skip truncating ON COMMIT DELETE ROWS
                 * tables, as they must still be empty.
                 */
                if (MyXactAccessedTempRel)
                    oids_to_truncate = lappend_oid(oids_to_truncate, oc->relid);
                break;
            case ONCOMMIT_DROP:
                {
                    ObjectAddress object;

                    object.classId = RelationRelationId;
                    object.objectId = oc->relid;
                    object.objectSubId = 0;

                    /*
                     * Since this is an automatic drop, rather than one
                     * directly initiated by the user, we pass the
                     * PERFORM_DELETION_INTERNAL flag.
                     */
                    performDeletion(&object,
                                    DROP_CASCADE, PERFORM_DELETION_INTERNAL);

                    /*
                     * Note that table deletion will call
                     * remove_on_commit_action, so the entry should get marked
                     * as deleted.
                     */
                    Assert(oc->deleting_subid != InvalidSubTransactionId);
                    break;
                }
        }
    }
    if (oids_to_truncate != NIL)
    {
        heap_truncate(oids_to_truncate);
        CommandCounterIncrement();      /* XXX needed? */
    }
}

/*
 * Post-commit or post-abort cleanup for ON COMMIT management.
 *
 * All we do here is remove no-longer-needed OnCommitItem entries.
 *
 * During commit, remove entries that were deleted during this transaction;
 * during abort, remove those created during this transaction.
 */
void
AtEOXact_on_commit_actions(bool isCommit)
{
    ListCell   *cur_item;
    ListCell   *prev_item;

    prev_item = NULL;
    cur_item = list_head(on_commits);

    while (cur_item != NULL)
    {
        OnCommitItem *oc = (OnCommitItem *) lfirst(cur_item);

        if (isCommit ? oc->deleting_subid != InvalidSubTransactionId :
            oc->creating_subid != InvalidSubTransactionId)
        {
            /* cur_item must be removed */
            on_commits = list_delete_cell(on_commits, cur_item, prev_item);
            pfree(oc);
            if (prev_item)
                cur_item = lnext(prev_item);
            else
                cur_item = list_head(on_commits);
        }
        else
        {
            /* cur_item must be preserved */
            oc->creating_subid = InvalidSubTransactionId;
            oc->deleting_subid = InvalidSubTransactionId;
            prev_item = cur_item;
            cur_item = lnext(prev_item);
        }
    }
}

/*
 * Post-subcommit or post-subabort cleanup for ON COMMIT management.
 *
 * During subabort, we can immediately remove entries created during this
 * subtransaction.  During subcommit, just relabel entries marked during
 * this subtransaction as being the parent's responsibility.
 */
void
AtEOSubXact_on_commit_actions(bool isCommit, SubTransactionId mySubid,
                              SubTransactionId parentSubid)
{
    ListCell   *cur_item;
    ListCell   *prev_item;

    prev_item = NULL;
    cur_item = list_head(on_commits);

    while (cur_item != NULL)
    {
        OnCommitItem *oc = (OnCommitItem *) lfirst(cur_item);

        if (!isCommit && oc->creating_subid == mySubid)
        {
            /* cur_item must be removed */
            on_commits = list_delete_cell(on_commits, cur_item, prev_item);
            pfree(oc);
            if (prev_item)
                cur_item = lnext(prev_item);
            else
                cur_item = list_head(on_commits);
        }
        else
        {
            /* cur_item must be preserved */
            if (oc->creating_subid == mySubid)
                oc->creating_subid = parentSubid;
            if (oc->deleting_subid == mySubid)
                oc->deleting_subid = isCommit ? parentSubid : InvalidSubTransactionId;
            prev_item = cur_item;
            cur_item = lnext(prev_item);
        }
    }
}

/*
 * This is intended as a callback for RangeVarGetRelidExtended().  It allows
 * the relation to be locked only if (1) it's a plain table, materialized
 * view, or TOAST table and (2) the current user is the owner (or the
 * superuser).  This meets the permission-checking needs of CLUSTER, REINDEX
 * TABLE, and REFRESH MATERIALIZED VIEW; we expose it here so that it can be
 * used by all.
 */
void
RangeVarCallbackOwnsTable(const RangeVar *relation,
                          Oid relId, Oid oldRelId, void *arg)
{
    char        relkind;

    /* Nothing to do if the relation was not found. */
    if (!OidIsValid(relId))
        return;

    /*
     * If the relation does exist, check whether it's an index.  But note that
     * the relation might have been dropped between the time we did the name
     * lookup and now.  In that case, there's nothing to do.
     */
    relkind = get_rel_relkind(relId);
    if (!relkind)
        return;
    if (relkind != RELKIND_RELATION && relkind != RELKIND_TOASTVALUE &&
        relkind != RELKIND_MATVIEW)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not a table or materialized view", relation->relname)));

    /* Check permissions */
    if (!pg_class_ownercheck(relId, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS, relation->relname);
}

/*
 * Common RangeVarGetRelid callback for rename, set schema, and alter table
 * processing.
 */
static void
RangeVarCallbackForAlterRelation(const RangeVar *rv, Oid relid, Oid oldrelid,
                                 void *arg)
{
    Node       *stmt = (Node *) arg;
    ObjectType  reltype;
    HeapTuple   tuple;
    Form_pg_class classform;
    AclResult   aclresult;
    char        relkind;

    tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
    if (!HeapTupleIsValid(tuple))
        return;                 /* concurrently dropped */
    classform = (Form_pg_class) GETSTRUCT(tuple);
    relkind = classform->relkind;

    /* Must own relation. */
    if (!pg_class_ownercheck(relid, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS, rv->relname);

    /* No system table modifications unless explicitly allowed. */
    if (!allowSystemTableMods && IsSystemClass(classform))
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("permission denied: \"%s\" is a system catalog",
                        rv->relname)));

    /*
     * Extract the specified relation type from the statement parse tree.
     *
     * Also, for ALTER .. RENAME, check permissions: the user must (still)
     * have CREATE rights on the containing namespace.
     */
    if (IsA(stmt, RenameStmt))
    {
        aclresult = pg_namespace_aclcheck(classform->relnamespace,
                                          GetUserId(), ACL_CREATE);
        if (aclresult != ACLCHECK_OK)
            aclcheck_error(aclresult, ACL_KIND_NAMESPACE,
                           get_namespace_name(classform->relnamespace));
        reltype = ((RenameStmt *) stmt)->renameType;
    }
    else if (IsA(stmt, AlterObjectSchemaStmt))
        reltype = ((AlterObjectSchemaStmt *) stmt)->objectType;

    else if (IsA(stmt, AlterTableStmt))
        reltype = ((AlterTableStmt *) stmt)->relkind;
    else
    {
        reltype = OBJECT_TABLE; /* placate compiler */
        elog(ERROR, "unrecognized node type: %d", (int) nodeTag(stmt));
    }

    /*
     * For compatibility with prior releases, we allow ALTER TABLE to be used
     * with most other types of relations (but not composite types). We allow
     * similar flexibility for ALTER INDEX in the case of RENAME, but not
     * otherwise.  Otherwise, the user must select the correct form of the
     * command for the relation at issue.
     */
    if (reltype == OBJECT_SEQUENCE && relkind != RELKIND_SEQUENCE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not a sequence", rv->relname)));

    if (reltype == OBJECT_VIEW && relkind != RELKIND_VIEW)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not a view", rv->relname)));

    if (reltype == OBJECT_MATVIEW && relkind != RELKIND_MATVIEW)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not a materialized view", rv->relname)));

    if (reltype == OBJECT_FOREIGN_TABLE && relkind != RELKIND_FOREIGN_TABLE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not a foreign table", rv->relname)));

    if (reltype == OBJECT_TYPE && relkind != RELKIND_COMPOSITE_TYPE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not a composite type", rv->relname)));

    if (reltype == OBJECT_INDEX && relkind != RELKIND_INDEX
        && !IsA(stmt, RenameStmt))
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not an index", rv->relname)));

    /*
     * Don't allow ALTER TABLE on composite types. We want people to use ALTER
     * TYPE for that.
     */
    if (reltype != OBJECT_TYPE && relkind == RELKIND_COMPOSITE_TYPE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is a composite type", rv->relname),
                 errhint("Use ALTER TYPE instead.")));

    if (reltype != OBJECT_FOREIGN_TABLE && relkind == RELKIND_FOREIGN_TABLE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is a foreign table", rv->relname),
                 errhint("Use ALTER FOREIGN TABLE instead.")));

    /*
     * Don't allow ALTER TABLE .. SET SCHEMA on relations that can't be moved
     * to a different schema, such as indexes and TOAST tables.
     */
    if (IsA(stmt, AlterObjectSchemaStmt) && relkind != RELKIND_RELATION
        && relkind != RELKIND_VIEW && relkind != RELKIND_MATVIEW
        && relkind != RELKIND_SEQUENCE && relkind != RELKIND_FOREIGN_TABLE)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
            errmsg("\"%s\" is not a table, view, sequence, or foreign table",
                   rv->relname)));

    ReleaseSysCache(tuple);
}