indexcmds.c

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/*-------------------------------------------------------------------------
 *
 * indexcmds.c
 *    POSTGRES define and remove index code.
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/commands/indexcmds.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/htup_details.h"
#include "access/reloptions.h"
#include "access/xact.h"
#include "catalog/catalog.h"
#include "catalog/index.h"
#include "catalog/indexing.h"
#include "catalog/pg_opclass.h"
#include "catalog/pg_opfamily.h"
#include "catalog/pg_tablespace.h"
#include "catalog/pg_type.h"
#include "commands/comment.h"
#include "commands/dbcommands.h"
#include "commands/defrem.h"
#include "commands/tablecmds.h"
#include "commands/tablespace.h"
#include "mb/pg_wchar.h"
#include "miscadmin.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/clauses.h"
#include "optimizer/planner.h"
#include "parser/parse_coerce.h"
#include "parser/parse_func.h"
#include "parser/parse_oper.h"
#include "storage/lmgr.h"
#include "storage/proc.h"
#include "storage/procarray.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/snapmgr.h"
#include "utils/syscache.h"
#include "utils/tqual.h"


/* non-export function prototypes */
static void CheckPredicate(Expr *predicate);
static void ComputeIndexAttrs(IndexInfo *indexInfo,
                  Oid *typeOidP,
                  Oid *collationOidP,
                  Oid *classOidP,
                  int16 *colOptionP,
                  List *attList,
                  List *exclusionOpNames,
                  Oid relId,
                  char *accessMethodName, Oid accessMethodId,
                  bool amcanorder,
                  bool isconstraint);
static Oid GetIndexOpClass(List *opclass, Oid attrType,
                char *accessMethodName, Oid accessMethodId);
static char *ChooseIndexName(const char *tabname, Oid namespaceId,
                List *colnames, List *exclusionOpNames,
                bool primary, bool isconstraint);
static char *ChooseIndexNameAddition(List *colnames);
static List *ChooseIndexColumnNames(List *indexElems);
static void RangeVarCallbackForReindexIndex(const RangeVar *relation,
                                Oid relId, Oid oldRelId, void *arg);

/*
 * CheckIndexCompatible
 *      Determine whether an existing index definition is compatible with a
 *      prospective index definition, such that the existing index storage
 *      could become the storage of the new index, avoiding a rebuild.
 *
 * 'heapRelation': the relation the index would apply to.
 * 'accessMethodName': name of the AM to use.
 * 'attributeList': a list of IndexElem specifying columns and expressions
 *      to index on.
 * 'exclusionOpNames': list of names of exclusion-constraint operators,
 *      or NIL if not an exclusion constraint.
 *
 * This is tailored to the needs of ALTER TABLE ALTER TYPE, which recreates
 * any indexes that depended on a changing column from their pg_get_indexdef
 * or pg_get_constraintdef definitions.  We omit some of the sanity checks of
 * DefineIndex.  We assume that the old and new indexes have the same number
 * of columns and that if one has an expression column or predicate, both do.
 * Errors arising from the attribute list still apply.
 *
 * Most column type changes that can skip a table rewrite do not invalidate
 * indexes.  We ackowledge this when all operator classes, collations and
 * exclusion operators match.  Though we could further permit intra-opfamily
 * changes for btree and hash indexes, that adds subtle complexity with no
 * concrete benefit for core types.

 * When a comparison or exclusion operator has a polymorphic input type, the
 * actual input types must also match.  This defends against the possibility
 * that operators could vary behavior in response to get_fn_expr_argtype().
 * At present, this hazard is theoretical: check_exclusion_constraint() and
 * all core index access methods decline to set fn_expr for such calls.
 *
 * We do not yet implement a test to verify compatibility of expression
 * columns or predicates, so assume any such index is incompatible.
 */
bool
CheckIndexCompatible(Oid oldId,
                     RangeVar *heapRelation,
                     char *accessMethodName,
                     List *attributeList,
                     List *exclusionOpNames)
{
    bool        isconstraint;
    Oid        *typeObjectId;
    Oid        *collationObjectId;
    Oid        *classObjectId;
    Oid         accessMethodId;
    Oid         relationId;
    HeapTuple   tuple;
    Form_pg_index indexForm;
    Form_pg_am  accessMethodForm;
    bool        amcanorder;
    int16      *coloptions;
    IndexInfo  *indexInfo;
    int         numberOfAttributes;
    int         old_natts;
    bool        isnull;
    bool        ret = true;
    oidvector  *old_indclass;
    oidvector  *old_indcollation;
    Relation    irel;
    int         i;
    Datum       d;

    /* Caller should already have the relation locked in some way. */
    relationId = RangeVarGetRelid(heapRelation, NoLock, false);

    /*
     * We can pretend isconstraint = false unconditionally.  It only serves to
     * decide the text of an error message that should never happen for us.
     */
    isconstraint = false;

    numberOfAttributes = list_length(attributeList);
    Assert(numberOfAttributes > 0);
    Assert(numberOfAttributes <= INDEX_MAX_KEYS);

    /* look up the access method */
    tuple = SearchSysCache1(AMNAME, PointerGetDatum(accessMethodName));
    if (!HeapTupleIsValid(tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("access method \"%s\" does not exist",
                        accessMethodName)));
    accessMethodId = HeapTupleGetOid(tuple);
    accessMethodForm = (Form_pg_am) GETSTRUCT(tuple);
    amcanorder = accessMethodForm->amcanorder;
    ReleaseSysCache(tuple);

    /*
     * Compute the operator classes, collations, and exclusion operators for
     * the new index, so we can test whether it's compatible with the existing
     * one.  Note that ComputeIndexAttrs might fail here, but that's OK:
     * DefineIndex would have called this function with the same arguments
     * later on, and it would have failed then anyway.
     */
    indexInfo = makeNode(IndexInfo);
    indexInfo->ii_Expressions = NIL;
    indexInfo->ii_ExpressionsState = NIL;
    indexInfo->ii_PredicateState = NIL;
    indexInfo->ii_ExclusionOps = NULL;
    indexInfo->ii_ExclusionProcs = NULL;
    indexInfo->ii_ExclusionStrats = NULL;
    typeObjectId = (Oid *) palloc(numberOfAttributes * sizeof(Oid));
    collationObjectId = (Oid *) palloc(numberOfAttributes * sizeof(Oid));
    classObjectId = (Oid *) palloc(numberOfAttributes * sizeof(Oid));
    coloptions = (int16 *) palloc(numberOfAttributes * sizeof(int16));
    ComputeIndexAttrs(indexInfo,
                      typeObjectId, collationObjectId, classObjectId,
                      coloptions, attributeList,
                      exclusionOpNames, relationId,
                      accessMethodName, accessMethodId,
                      amcanorder, isconstraint);


    /* Get the soon-obsolete pg_index tuple. */
    tuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(oldId));
    if (!HeapTupleIsValid(tuple))
        elog(ERROR, "cache lookup failed for index %u", oldId);
    indexForm = (Form_pg_index) GETSTRUCT(tuple);

    /*
     * We don't assess expressions or predicates; assume incompatibility.
     * Also, if the index is invalid for any reason, treat it as incompatible.
     */
    if (!(heap_attisnull(tuple, Anum_pg_index_indpred) &&
          heap_attisnull(tuple, Anum_pg_index_indexprs) &&
          IndexIsValid(indexForm)))
    {
        ReleaseSysCache(tuple);
        return false;
    }

    /* Any change in operator class or collation breaks compatibility. */
    old_natts = indexForm->indnatts;
    Assert(old_natts == numberOfAttributes);

    d = SysCacheGetAttr(INDEXRELID, tuple, Anum_pg_index_indcollation, &isnull);
    Assert(!isnull);
    old_indcollation = (oidvector *) DatumGetPointer(d);

    d = SysCacheGetAttr(INDEXRELID, tuple, Anum_pg_index_indclass, &isnull);
    Assert(!isnull);
    old_indclass = (oidvector *) DatumGetPointer(d);

    ret = (memcmp(old_indclass->values, classObjectId,
                  old_natts * sizeof(Oid)) == 0 &&
           memcmp(old_indcollation->values, collationObjectId,
                  old_natts * sizeof(Oid)) == 0);

    ReleaseSysCache(tuple);

    if (!ret)
        return false;

    /* For polymorphic opcintype, column type changes break compatibility. */
    irel = index_open(oldId, AccessShareLock);  /* caller probably has a lock */
    for (i = 0; i < old_natts; i++)
    {
        if (IsPolymorphicType(get_opclass_input_type(classObjectId[i])) &&
            irel->rd_att->attrs[i]->atttypid != typeObjectId[i])
        {
            ret = false;
            break;
        }
    }

    /* Any change in exclusion operator selections breaks compatibility. */
    if (ret && indexInfo->ii_ExclusionOps != NULL)
    {
        Oid        *old_operators,
                   *old_procs;
        uint16     *old_strats;

        RelationGetExclusionInfo(irel, &old_operators, &old_procs, &old_strats);
        ret = memcmp(old_operators, indexInfo->ii_ExclusionOps,
                     old_natts * sizeof(Oid)) == 0;

        /* Require an exact input type match for polymorphic operators. */
        if (ret)
        {
            for (i = 0; i < old_natts && ret; i++)
            {
                Oid         left,
                            right;

                op_input_types(indexInfo->ii_ExclusionOps[i], &left, &right);
                if ((IsPolymorphicType(left) || IsPolymorphicType(right)) &&
                    irel->rd_att->attrs[i]->atttypid != typeObjectId[i])
                {
                    ret = false;
                    break;
                }
            }
        }
    }

    index_close(irel, NoLock);
    return ret;
}

/*
 * DefineIndex
 *      Creates a new index.
 *
 * 'stmt': IndexStmt describing the properties of the new index.
 * 'indexRelationId': normally InvalidOid, but during bootstrap can be
 *      nonzero to specify a preselected OID for the index.
 * 'is_alter_table': this is due to an ALTER rather than a CREATE operation.
 * 'check_rights': check for CREATE rights in the namespace.  (This should
 *      be true except when ALTER is deleting/recreating an index.)
 * 'skip_build': make the catalog entries but leave the index file empty;
 *      it will be filled later.
 * 'quiet': suppress the NOTICE chatter ordinarily provided for constraints.
 *
 * Returns the OID of the created index.
 */
Oid
DefineIndex(IndexStmt *stmt,
            Oid indexRelationId,
            bool is_alter_table,
            bool check_rights,
            bool skip_build,
            bool quiet)
{
    char       *indexRelationName;
    char       *accessMethodName;
    Oid        *typeObjectId;
    Oid        *collationObjectId;
    Oid        *classObjectId;
    Oid         accessMethodId;
    Oid         relationId;
    Oid         namespaceId;
    Oid         tablespaceId;
    List       *indexColNames;
    Relation    rel;
    Relation    indexRelation;
    HeapTuple   tuple;
    Form_pg_am  accessMethodForm;
    bool        amcanorder;
    RegProcedure amoptions;
    Datum       reloptions;
    int16      *coloptions;
    IndexInfo  *indexInfo;
    int         numberOfAttributes;
    TransactionId limitXmin;
    VirtualTransactionId *old_lockholders;
    VirtualTransactionId *old_snapshots;
    int         n_old_snapshots;
    LockRelId   heaprelid;
    LOCKTAG     heaplocktag;
    Snapshot    snapshot;
    int         i;

    /*
     * count attributes in index
     */
    numberOfAttributes = list_length(stmt->indexParams);
    if (numberOfAttributes <= 0)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                 errmsg("must specify at least one column")));
    if (numberOfAttributes > INDEX_MAX_KEYS)
        ereport(ERROR,
                (errcode(ERRCODE_TOO_MANY_COLUMNS),
                 errmsg("cannot use more than %d columns in an index",
                        INDEX_MAX_KEYS)));

    /*
     * Open heap relation, acquire a suitable lock on it, remember its OID
     *
     * Only SELECT ... FOR UPDATE/SHARE are allowed while doing a standard
     * index build; but for concurrent builds we allow INSERT/UPDATE/DELETE
     * (but not VACUUM).
     */
    rel = heap_openrv(stmt->relation,
                      (stmt->concurrent ? ShareUpdateExclusiveLock : ShareLock));

    relationId = RelationGetRelid(rel);
    namespaceId = RelationGetNamespace(rel);

    if (rel->rd_rel->relkind != RELKIND_RELATION &&
        rel->rd_rel->relkind != RELKIND_MATVIEW)
    {
        if (rel->rd_rel->relkind == RELKIND_FOREIGN_TABLE)

            /*
             * Custom error message for FOREIGN TABLE since the term is close
             * to a regular table and can confuse the user.
             */
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                     errmsg("cannot create index on foreign table \"%s\"",
                            RelationGetRelationName(rel))));
        else
            ereport(ERROR,
                    (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                     errmsg("\"%s\" is not a table",
                            RelationGetRelationName(rel))));
    }

    /*
     * Don't try to CREATE INDEX on temp tables of other backends.
     */
    if (RELATION_IS_OTHER_TEMP(rel))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("cannot create indexes on temporary tables of other sessions")));

    /*
     * Verify we (still) have CREATE rights in the rel's namespace.
     * (Presumably we did when the rel was created, but maybe not anymore.)
     * Skip check if caller doesn't want it.  Also skip check if
     * bootstrapping, since permissions machinery may not be working yet.
     */
    if (check_rights && !IsBootstrapProcessingMode())
    {
        AclResult   aclresult;

        aclresult = pg_namespace_aclcheck(namespaceId, GetUserId(),
                                          ACL_CREATE);
        if (aclresult != ACLCHECK_OK)
            aclcheck_error(aclresult, ACL_KIND_NAMESPACE,
                           get_namespace_name(namespaceId));
    }

    /*
     * Select tablespace to use.  If not specified, use default tablespace
     * (which may in turn default to database's default).
     */
    if (stmt->tableSpace)
    {
        tablespaceId = get_tablespace_oid(stmt->tableSpace, false);
    }
    else
    {
        tablespaceId = GetDefaultTablespace(rel->rd_rel->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));
    }

    /*
     * Force shared indexes into the pg_global tablespace.  This is a bit of a
     * hack but seems simpler than marking them in the BKI commands.  On the
     * other hand, if it's not shared, don't allow it to be placed there.
     */
    if (rel->rd_rel->relisshared)
        tablespaceId = GLOBALTABLESPACE_OID;
    else if (tablespaceId == GLOBALTABLESPACE_OID)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                 errmsg("only shared relations can be placed in pg_global tablespace")));

    /*
     * Choose the index column names.
     */
    indexColNames = ChooseIndexColumnNames(stmt->indexParams);

    /*
     * Select name for index if caller didn't specify
     */
    indexRelationName = stmt->idxname;
    if (indexRelationName == NULL)
        indexRelationName = ChooseIndexName(RelationGetRelationName(rel),
                                            namespaceId,
                                            indexColNames,
                                            stmt->excludeOpNames,
                                            stmt->primary,
                                            stmt->isconstraint);

    /*
     * look up the access method, verify it can handle the requested features
     */
    accessMethodName = stmt->accessMethod;
    tuple = SearchSysCache1(AMNAME, PointerGetDatum(accessMethodName));
    if (!HeapTupleIsValid(tuple))
    {
        /*
         * Hack to provide more-or-less-transparent updating of old RTREE
         * indexes to GiST: if RTREE is requested and not found, use GIST.
         */
        if (strcmp(accessMethodName, "rtree") == 0)
        {
            ereport(NOTICE,
                    (errmsg("substituting access method \"gist\" for obsolete method \"rtree\"")));
            accessMethodName = "gist";
            tuple = SearchSysCache1(AMNAME, PointerGetDatum(accessMethodName));
        }

        if (!HeapTupleIsValid(tuple))
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_OBJECT),
                     errmsg("access method \"%s\" does not exist",
                            accessMethodName)));
    }
    accessMethodId = HeapTupleGetOid(tuple);
    accessMethodForm = (Form_pg_am) GETSTRUCT(tuple);

    if (stmt->unique && !accessMethodForm->amcanunique)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
               errmsg("access method \"%s\" does not support unique indexes",
                      accessMethodName)));
    if (numberOfAttributes > 1 && !accessMethodForm->amcanmulticol)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
          errmsg("access method \"%s\" does not support multicolumn indexes",
                 accessMethodName)));
    if (stmt->excludeOpNames && !OidIsValid(accessMethodForm->amgettuple))
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
        errmsg("access method \"%s\" does not support exclusion constraints",
               accessMethodName)));

    amcanorder = accessMethodForm->amcanorder;
    amoptions = accessMethodForm->amoptions;

    ReleaseSysCache(tuple);

    /*
     * Validate predicate, if given
     */
    if (stmt->whereClause)
        CheckPredicate((Expr *) stmt->whereClause);

    /*
     * Parse AM-specific options, convert to text array form, validate.
     */
    reloptions = transformRelOptions((Datum) 0, stmt->options,
                                     NULL, NULL, false, false);

    (void) index_reloptions(amoptions, reloptions, true);

    /*
     * Prepare arguments for index_create, primarily an IndexInfo structure.
     * Note that ii_Predicate must be in implicit-AND format.
     */
    indexInfo = makeNode(IndexInfo);
    indexInfo->ii_NumIndexAttrs = numberOfAttributes;
    indexInfo->ii_Expressions = NIL;    /* for now */
    indexInfo->ii_ExpressionsState = NIL;
    indexInfo->ii_Predicate = make_ands_implicit((Expr *) stmt->whereClause);
    indexInfo->ii_PredicateState = NIL;
    indexInfo->ii_ExclusionOps = NULL;
    indexInfo->ii_ExclusionProcs = NULL;
    indexInfo->ii_ExclusionStrats = NULL;
    indexInfo->ii_Unique = stmt->unique;
    /* In a concurrent build, mark it not-ready-for-inserts */
    indexInfo->ii_ReadyForInserts = !stmt->concurrent;
    indexInfo->ii_Concurrent = stmt->concurrent;
    indexInfo->ii_BrokenHotChain = false;

    typeObjectId = (Oid *) palloc(numberOfAttributes * sizeof(Oid));
    collationObjectId = (Oid *) palloc(numberOfAttributes * sizeof(Oid));
    classObjectId = (Oid *) palloc(numberOfAttributes * sizeof(Oid));
    coloptions = (int16 *) palloc(numberOfAttributes * sizeof(int16));
    ComputeIndexAttrs(indexInfo,
                      typeObjectId, collationObjectId, classObjectId,
                      coloptions, stmt->indexParams,
                      stmt->excludeOpNames, relationId,
                      accessMethodName, accessMethodId,
                      amcanorder, stmt->isconstraint);

    /*
     * Extra checks when creating a PRIMARY KEY index.
     */
    if (stmt->primary)
        index_check_primary_key(rel, indexInfo, is_alter_table);

    /*
     * Report index creation if appropriate (delay this till after most of the
     * error checks)
     */
    if (stmt->isconstraint && !quiet)
    {
        const char *constraint_type;

        if (stmt->primary)
            constraint_type = "PRIMARY KEY";
        else if (stmt->unique)
            constraint_type = "UNIQUE";
        else if (stmt->excludeOpNames != NIL)
            constraint_type = "EXCLUDE";
        else
        {
            elog(ERROR, "unknown constraint type");
            constraint_type = NULL;     /* keep compiler quiet */
        }

        ereport(DEBUG1,
          (errmsg("%s %s will create implicit index \"%s\" for table \"%s\"",
                  is_alter_table ? "ALTER TABLE / ADD" : "CREATE TABLE /",
                  constraint_type,
                  indexRelationName, RelationGetRelationName(rel))));
    }

    /*
     * A valid stmt->oldNode implies that we already have a built form of the
     * index.  The caller should also decline any index build.
     */
    Assert(!OidIsValid(stmt->oldNode) || (skip_build && !stmt->concurrent));

    /*
     * Make the catalog entries for the index, including constraints. Then, if
     * not skip_build || concurrent, actually build the index.
     */
    indexRelationId =
        index_create(rel, indexRelationName, indexRelationId, stmt->oldNode,
                     indexInfo, indexColNames,
                     accessMethodId, tablespaceId,
                     collationObjectId, classObjectId,
                     coloptions, reloptions, stmt->primary,
                     stmt->isconstraint, stmt->deferrable, stmt->initdeferred,
                     allowSystemTableMods,
                     skip_build || stmt->concurrent,
                     stmt->concurrent, !check_rights);

    /* Add any requested comment */
    if (stmt->idxcomment != NULL)
        CreateComments(indexRelationId, RelationRelationId, 0,
                       stmt->idxcomment);

    if (!stmt->concurrent)
    {
        /* Close the heap and we're done, in the non-concurrent case */
        heap_close(rel, NoLock);
        return indexRelationId;
    }

    /* save lockrelid and locktag for below, then close rel */
    heaprelid = rel->rd_lockInfo.lockRelId;
    SET_LOCKTAG_RELATION(heaplocktag, heaprelid.dbId, heaprelid.relId);
    heap_close(rel, NoLock);

    /*
     * For a concurrent build, it's important to make the catalog entries
     * visible to other transactions before we start to build the index. That
     * will prevent them from making incompatible HOT updates.  The new index
     * will be marked not indisready and not indisvalid, so that no one else
     * tries to either insert into it or use it for queries.
     *
     * We must commit our current transaction so that the index becomes
     * visible; then start another.  Note that all the data structures we just
     * built are lost in the commit.  The only data we keep past here are the
     * relation IDs.
     *
     * Before committing, get a session-level lock on the table, to ensure
     * that neither it nor the index can be dropped before we finish. This
     * cannot block, even if someone else is waiting for access, because we
     * already have the same lock within our transaction.
     *
     * Note: we don't currently bother with a session lock on the index,
     * because there are no operations that could change its state while we
     * hold lock on the parent table.  This might need to change later.
     */
    LockRelationIdForSession(&heaprelid, ShareUpdateExclusiveLock);

    PopActiveSnapshot();
    CommitTransactionCommand();
    StartTransactionCommand();

    /*
     * Phase 2 of concurrent index build (see comments for validate_index()
     * for an overview of how this works)
     *
     * Now we must wait until no running transaction could have the table open
     * with the old list of indexes.  To do this, inquire which xacts
     * currently would conflict with ShareLock on the table -- ie, which ones
     * have a lock that permits writing the table.  Then wait for each of
     * these xacts to commit or abort.  Note we do not need to worry about
     * xacts that open the table for writing after this point; they will see
     * the new index when they open it.
     *
     * Note: the reason we use actual lock acquisition here, rather than just
     * checking the ProcArray and sleeping, is that deadlock is possible if
     * one of the transactions in question is blocked trying to acquire an
     * exclusive lock on our table.  The lock code will detect deadlock and
     * error out properly.
     *
     * Note: GetLockConflicts() never reports our own xid, hence we need not
     * check for that.  Also, prepared xacts are not reported, which is fine
     * since they certainly aren't going to do anything more.
     */
    old_lockholders = GetLockConflicts(&heaplocktag, ShareLock);

    while (VirtualTransactionIdIsValid(*old_lockholders))
    {
        VirtualXactLock(*old_lockholders, true);
        old_lockholders++;
    }

    /*
     * At this moment we are sure that there are no transactions with the
     * table open for write that don't have this new index in their list of
     * indexes.  We have waited out all the existing transactions and any new
     * transaction will have the new index in its list, but the index is still
     * marked as "not-ready-for-inserts".  The index is consulted while
     * deciding HOT-safety though.  This arrangement ensures that no new HOT
     * chains can be created where the new tuple and the old tuple in the
     * chain have different index keys.
     *
     * We now take a new snapshot, and build the index using all tuples that
     * are visible in this snapshot.  We can be sure that any HOT updates to
     * these tuples will be compatible with the index, since any updates made
     * by transactions that didn't know about the index are now committed or
     * rolled back.  Thus, each visible tuple is either the end of its
     * HOT-chain or the extension of the chain is HOT-safe for this index.
     */

    /* Open and lock the parent heap relation */
    rel = heap_openrv(stmt->relation, ShareUpdateExclusiveLock);

    /* And the target index relation */
    indexRelation = index_open(indexRelationId, RowExclusiveLock);

    /* Set ActiveSnapshot since functions in the indexes may need it */
    PushActiveSnapshot(GetTransactionSnapshot());

    /* We have to re-build the IndexInfo struct, since it was lost in commit */
    indexInfo = BuildIndexInfo(indexRelation);
    Assert(!indexInfo->ii_ReadyForInserts);
    indexInfo->ii_Concurrent = true;
    indexInfo->ii_BrokenHotChain = false;

    /* Now build the index */
    index_build(rel, indexRelation, indexInfo, stmt->primary, false);

    /* Close both the relations, but keep the locks */
    heap_close(rel, NoLock);
    index_close(indexRelation, NoLock);

    /*
     * Update the pg_index row to mark the index as ready for inserts. Once we
     * commit this transaction, any new transactions that open the table must
     * insert new entries into the index for insertions and non-HOT updates.
     */
    index_set_state_flags(indexRelationId, INDEX_CREATE_SET_READY);

    /* we can do away with our snapshot */
    PopActiveSnapshot();

    /*
     * Commit this transaction to make the indisready update visible.
     */
    CommitTransactionCommand();
    StartTransactionCommand();

    /*
     * Phase 3 of concurrent index build
     *
     * We once again wait until no transaction can have the table open with
     * the index marked as read-only for updates.
     */
    old_lockholders = GetLockConflicts(&heaplocktag, ShareLock);

    while (VirtualTransactionIdIsValid(*old_lockholders))
    {
        VirtualXactLock(*old_lockholders, true);
        old_lockholders++;
    }

    /*
     * Now take the "reference snapshot" that will be used by validate_index()
     * to filter candidate tuples.  Beware!  There might still be snapshots in
     * use that treat some transaction as in-progress that our reference
     * snapshot treats as committed.  If such a recently-committed transaction
     * deleted tuples in the table, we will not include them in the index; yet
     * those transactions which see the deleting one as still-in-progress will
     * expect such tuples to be there once we mark the index as valid.
     *
     * We solve this by waiting for all endangered transactions to exit before
     * we mark the index as valid.
     *
     * We also set ActiveSnapshot to this snap, since functions in indexes may
     * need a snapshot.
     */
    snapshot = RegisterSnapshot(GetTransactionSnapshot());
    PushActiveSnapshot(snapshot);

    /*
     * Scan the index and the heap, insert any missing index entries.
     */
    validate_index(relationId, indexRelationId, snapshot);

    /*
     * Drop the reference snapshot.  We must do this before waiting out other
     * snapshot holders, else we will deadlock against other processes also
     * doing CREATE INDEX CONCURRENTLY, which would see our snapshot as one
     * they must wait for.  But first, save the snapshot's xmin to use as
     * limitXmin for GetCurrentVirtualXIDs().
     */
    limitXmin = snapshot->xmin;

    PopActiveSnapshot();
    UnregisterSnapshot(snapshot);

    /*
     * The index is now valid in the sense that it contains all currently
     * interesting tuples.  But since it might not contain tuples deleted just
     * before the reference snap was taken, we have to wait out any
     * transactions that might have older snapshots.  Obtain a list of VXIDs
     * of such transactions, and wait for them individually.
     *
     * We can exclude any running transactions that have xmin > the xmin of
     * our reference snapshot; their oldest snapshot must be newer than ours.
     * We can also exclude any transactions that have xmin = zero, since they
     * evidently have no live snapshot at all (and any one they might be in
     * process of taking is certainly newer than ours).  Transactions in other
     * DBs can be ignored too, since they'll never even be able to see this
     * index.
     *
     * We can also exclude autovacuum processes and processes running manual
     * lazy VACUUMs, because they won't be fazed by missing index entries
     * either.  (Manual ANALYZEs, however, can't be excluded because they
     * might be within transactions that are going to do arbitrary operations
     * later.)
     *
     * Also, GetCurrentVirtualXIDs never reports our own vxid, so we need not
     * check for that.
     *
     * If a process goes idle-in-transaction with xmin zero, we do not need to
     * wait for it anymore, per the above argument.  We do not have the
     * infrastructure right now to stop waiting if that happens, but we can at
     * least avoid the folly of waiting when it is idle at the time we would
     * begin to wait.  We do this by repeatedly rechecking the output of
     * GetCurrentVirtualXIDs.  If, during any iteration, a particular vxid
     * doesn't show up in the output, we know we can forget about it.
     */
    old_snapshots = GetCurrentVirtualXIDs(limitXmin, true, false,
                                          PROC_IS_AUTOVACUUM | PROC_IN_VACUUM,
                                          &n_old_snapshots);

    for (i = 0; i < n_old_snapshots; i++)
    {
        if (!VirtualTransactionIdIsValid(old_snapshots[i]))
            continue;           /* found uninteresting in previous cycle */

        if (i > 0)
        {
            /* see if anything's changed ... */
            VirtualTransactionId *newer_snapshots;
            int         n_newer_snapshots;
            int         j;
            int         k;

            newer_snapshots = GetCurrentVirtualXIDs(limitXmin,
                                                    true, false,
                                         PROC_IS_AUTOVACUUM | PROC_IN_VACUUM,
                                                    &n_newer_snapshots);
            for (j = i; j < n_old_snapshots; j++)
            {
                if (!VirtualTransactionIdIsValid(old_snapshots[j]))
                    continue;   /* found uninteresting in previous cycle */
                for (k = 0; k < n_newer_snapshots; k++)
                {
                    if (VirtualTransactionIdEquals(old_snapshots[j],
                                                   newer_snapshots[k]))
                        break;
                }
                if (k >= n_newer_snapshots)     /* not there anymore */
                    SetInvalidVirtualTransactionId(old_snapshots[j]);
            }
            pfree(newer_snapshots);
        }

        if (VirtualTransactionIdIsValid(old_snapshots[i]))
            VirtualXactLock(old_snapshots[i], true);
    }

    /*
     * Index can now be marked valid -- update its pg_index entry
     */
    index_set_state_flags(indexRelationId, INDEX_CREATE_SET_VALID);

    /*
     * The pg_index update will cause backends (including this one) to update
     * relcache entries for the index itself, but we should also send a
     * relcache inval on the parent table to force replanning of cached plans.
     * Otherwise existing sessions might fail to use the new index where it
     * would be useful.  (Note that our earlier commits did not create reasons
     * to replan; so relcache flush on the index itself was sufficient.)
     */
    CacheInvalidateRelcacheByRelid(heaprelid.relId);

    /*
     * Last thing to do is release the session-level lock on the parent table.
     */
    UnlockRelationIdForSession(&heaprelid, ShareUpdateExclusiveLock);

    return indexRelationId;
}


/*
 * CheckMutability
 *      Test whether given expression is mutable
 */
static bool
CheckMutability(Expr *expr)
{
    /*
     * First run the expression through the planner.  This has a couple of
     * important consequences.  First, function default arguments will get
     * inserted, which may affect volatility (consider "default now()").
     * Second, inline-able functions will get inlined, which may allow us to
     * conclude that the function is really less volatile than it's marked. As
     * an example, polymorphic functions must be marked with the most volatile
     * behavior that they have for any input type, but once we inline the
     * function we may be able to conclude that it's not so volatile for the
     * particular input type we're dealing with.
     *
     * We assume here that expression_planner() won't scribble on its input.
     */
    expr = expression_planner(expr);

    /* Now we can search for non-immutable functions */
    return contain_mutable_functions((Node *) expr);
}


/*
 * CheckPredicate
 *      Checks that the given partial-index predicate is valid.
 *
 * This used to also constrain the form of the predicate to forms that
 * indxpath.c could do something with.  However, that seems overly
 * restrictive.  One useful application of partial indexes is to apply
 * a UNIQUE constraint across a subset of a table, and in that scenario
 * any evaluatable predicate will work.  So accept any predicate here
 * (except ones requiring a plan), and let indxpath.c fend for itself.
 */
static void
CheckPredicate(Expr *predicate)
{
    /*
     * transformExpr() should have already rejected subqueries, aggregates,
     * and window functions, based on the EXPR_KIND_ for a predicate.
     */

    /*
     * A predicate using mutable functions is probably wrong, for the same
     * reasons that we don't allow an index expression to use one.
     */
    if (CheckMutability(predicate))
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
           errmsg("functions in index predicate must be marked IMMUTABLE")));
}

/*
 * Compute per-index-column information, including indexed column numbers
 * or index expressions, opclasses, and indoptions.
 */
static void
ComputeIndexAttrs(IndexInfo *indexInfo,
                  Oid *typeOidP,
                  Oid *collationOidP,
                  Oid *classOidP,
                  int16 *colOptionP,
                  List *attList,    /* list of IndexElem's */
                  List *exclusionOpNames,
                  Oid relId,
                  char *accessMethodName,
                  Oid accessMethodId,
                  bool amcanorder,
                  bool isconstraint)
{
    ListCell   *nextExclOp;
    ListCell   *lc;
    int         attn;

    /* Allocate space for exclusion operator info, if needed */
    if (exclusionOpNames)
    {
        int         ncols = list_length(attList);

        Assert(list_length(exclusionOpNames) == ncols);
        indexInfo->ii_ExclusionOps = (Oid *) palloc(sizeof(Oid) * ncols);
        indexInfo->ii_ExclusionProcs = (Oid *) palloc(sizeof(Oid) * ncols);
        indexInfo->ii_ExclusionStrats = (uint16 *) palloc(sizeof(uint16) * ncols);
        nextExclOp = list_head(exclusionOpNames);
    }
    else
        nextExclOp = NULL;

    /*
     * process attributeList
     */
    attn = 0;
    foreach(lc, attList)
    {
        IndexElem  *attribute = (IndexElem *) lfirst(lc);
        Oid         atttype;
        Oid         attcollation;

        /*
         * Process the column-or-expression to be indexed.
         */
        if (attribute->name != NULL)
        {
            /* Simple index attribute */
            HeapTuple   atttuple;
            Form_pg_attribute attform;

            Assert(attribute->expr == NULL);
            atttuple = SearchSysCacheAttName(relId, attribute->name);
            if (!HeapTupleIsValid(atttuple))
            {
                /* difference in error message spellings is historical */
                if (isconstraint)
                    ereport(ERROR,
                            (errcode(ERRCODE_UNDEFINED_COLUMN),
                          errmsg("column \"%s\" named in key does not exist",
                                 attribute->name)));
                else
                    ereport(ERROR,
                            (errcode(ERRCODE_UNDEFINED_COLUMN),
                             errmsg("column \"%s\" does not exist",
                                    attribute->name)));
            }
            attform = (Form_pg_attribute) GETSTRUCT(atttuple);
            indexInfo->ii_KeyAttrNumbers[attn] = attform->attnum;
            atttype = attform->atttypid;
            attcollation = attform->attcollation;
            ReleaseSysCache(atttuple);
        }
        else
        {
            /* Index expression */
            Node       *expr = attribute->expr;

            Assert(expr != NULL);
            atttype = exprType(expr);
            attcollation = exprCollation(expr);

            /*
             * Strip any top-level COLLATE clause.  This ensures that we treat
             * "x COLLATE y" and "(x COLLATE y)" alike.
             */
            while (IsA(expr, CollateExpr))
                expr = (Node *) ((CollateExpr *) expr)->arg;

            if (IsA(expr, Var) &&
                ((Var *) expr)->varattno != InvalidAttrNumber)
            {
                /*
                 * User wrote "(column)" or "(column COLLATE something)".
                 * Treat it like simple attribute anyway.
                 */
                indexInfo->ii_KeyAttrNumbers[attn] = ((Var *) expr)->varattno;
            }
            else
            {
                indexInfo->ii_KeyAttrNumbers[attn] = 0; /* marks expression */
                indexInfo->ii_Expressions = lappend(indexInfo->ii_Expressions,
                                                    expr);

                /*
                 * transformExpr() should have already rejected subqueries,
                 * aggregates, and window functions, based on the EXPR_KIND_
                 * for an index expression.
                 */

                /*
                 * A expression using mutable functions is probably wrong,
                 * since if you aren't going to get the same result for the
                 * same data every time, it's not clear what the index entries
                 * mean at all.
                 */
                if (CheckMutability((Expr *) expr))
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
                             errmsg("functions in index expression must be marked IMMUTABLE")));
            }
        }

        typeOidP[attn] = atttype;

        /*
         * Apply collation override if any
         */
        if (attribute->collation)
            attcollation = get_collation_oid(attribute->collation, false);

        /*
         * Check we have a collation iff it's a collatable type.  The only
         * expected failures here are (1) COLLATE applied to a noncollatable
         * type, or (2) index expression had an unresolved collation.  But we
         * might as well code this to be a complete consistency check.
         */
        if (type_is_collatable(atttype))
        {
            if (!OidIsValid(attcollation))
                ereport(ERROR,
                        (errcode(ERRCODE_INDETERMINATE_COLLATION),
                         errmsg("could not determine which collation to use for index expression"),
                         errhint("Use the COLLATE clause to set the collation explicitly.")));
        }
        else
        {
            if (OidIsValid(attcollation))
                ereport(ERROR,
                        (errcode(ERRCODE_DATATYPE_MISMATCH),
                         errmsg("collations are not supported by type %s",
                                format_type_be(atttype))));
        }

        collationOidP[attn] = attcollation;

        /*
         * Identify the opclass to use.
         */
        classOidP[attn] = GetIndexOpClass(attribute->opclass,
                                          atttype,
                                          accessMethodName,
                                          accessMethodId);

        /*
         * Identify the exclusion operator, if any.
         */
        if (nextExclOp)
        {
            List       *opname = (List *) lfirst(nextExclOp);
            Oid         opid;
            Oid         opfamily;
            int         strat;

            /*
             * Find the operator --- it must accept the column datatype
             * without runtime coercion (but binary compatibility is OK)
             */
            opid = compatible_oper_opid(opname, atttype, atttype, false);

            /*
             * Only allow commutative operators to be used in exclusion
             * constraints. If X conflicts with Y, but Y does not conflict
             * with X, bad things will happen.
             */
            if (get_commutator(opid) != opid)
                ereport(ERROR,
                        (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                         errmsg("operator %s is not commutative",
                                format_operator(opid)),
                         errdetail("Only commutative operators can be used in exclusion constraints.")));

            /*
             * Operator must be a member of the right opfamily, too
             */
            opfamily = get_opclass_family(classOidP[attn]);
            strat = get_op_opfamily_strategy(opid, opfamily);
            if (strat == 0)
            {
                HeapTuple   opftuple;
                Form_pg_opfamily opfform;

                /*
                 * attribute->opclass might not explicitly name the opfamily,
                 * so fetch the name of the selected opfamily for use in the
                 * error message.
                 */
                opftuple = SearchSysCache1(OPFAMILYOID,
                                           ObjectIdGetDatum(opfamily));
                if (!HeapTupleIsValid(opftuple))
                    elog(ERROR, "cache lookup failed for opfamily %u",
                         opfamily);
                opfform = (Form_pg_opfamily) GETSTRUCT(opftuple);

                ereport(ERROR,
                        (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                         errmsg("operator %s is not a member of operator family \"%s\"",
                                format_operator(opid),
                                NameStr(opfform->opfname)),
                         errdetail("The exclusion operator must be related to the index operator class for the constraint.")));
            }

            indexInfo->ii_ExclusionOps[attn] = opid;
            indexInfo->ii_ExclusionProcs[attn] = get_opcode(opid);
            indexInfo->ii_ExclusionStrats[attn] = strat;
            nextExclOp = lnext(nextExclOp);
        }

        /*
         * Set up the per-column options (indoption field).  For now, this is
         * zero for any un-ordered index, while ordered indexes have DESC and
         * NULLS FIRST/LAST options.
         */
        colOptionP[attn] = 0;
        if (amcanorder)
        {
            /* default ordering is ASC */
            if (attribute->ordering == SORTBY_DESC)
                colOptionP[attn] |= INDOPTION_DESC;
            /* default null ordering is LAST for ASC, FIRST for DESC */
            if (attribute->nulls_ordering == SORTBY_NULLS_DEFAULT)
            {
                if (attribute->ordering == SORTBY_DESC)
                    colOptionP[attn] |= INDOPTION_NULLS_FIRST;
            }
            else if (attribute->nulls_ordering == SORTBY_NULLS_FIRST)
                colOptionP[attn] |= INDOPTION_NULLS_FIRST;
        }
        else
        {
            /* index AM does not support ordering */
            if (attribute->ordering != SORTBY_DEFAULT)
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("access method \"%s\" does not support ASC/DESC options",
                                accessMethodName)));
            if (attribute->nulls_ordering != SORTBY_NULLS_DEFAULT)
                ereport(ERROR,
                        (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                         errmsg("access method \"%s\" does not support NULLS FIRST/LAST options",
                                accessMethodName)));
        }

        attn++;
    }
}

/*
 * Resolve possibly-defaulted operator class specification
 */
static Oid
GetIndexOpClass(List *opclass, Oid attrType,
                char *accessMethodName, Oid accessMethodId)
{
    char       *schemaname;
    char       *opcname;
    HeapTuple   tuple;
    Oid         opClassId,
                opInputType;

    /*
     * Release 7.0 removed network_ops, timespan_ops, and datetime_ops, so we
     * ignore those opclass names so the default *_ops is used.  This can be
     * removed in some later release.  bjm 2000/02/07
     *
     * Release 7.1 removes lztext_ops, so suppress that too for a while.  tgl
     * 2000/07/30
     *
     * Release 7.2 renames timestamp_ops to timestamptz_ops, so suppress that
     * too for awhile.  I'm starting to think we need a better approach. tgl
     * 2000/10/01
     *
     * Release 8.0 removes bigbox_ops (which was dead code for a long while
     * anyway).  tgl 2003/11/11
     */
    if (list_length(opclass) == 1)
    {
        char       *claname = strVal(linitial(opclass));

        if (strcmp(claname, "network_ops") == 0 ||
            strcmp(claname, "timespan_ops") == 0 ||
            strcmp(claname, "datetime_ops") == 0 ||
            strcmp(claname, "lztext_ops") == 0 ||
            strcmp(claname, "timestamp_ops") == 0 ||
            strcmp(claname, "bigbox_ops") == 0)
            opclass = NIL;
    }

    if (opclass == NIL)
    {
        /* no operator class specified, so find the default */
        opClassId = GetDefaultOpClass(attrType, accessMethodId);
        if (!OidIsValid(opClassId))
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_OBJECT),
                     errmsg("data type %s has no default operator class for access method \"%s\"",
                            format_type_be(attrType), accessMethodName),
                     errhint("You must specify an operator class for the index or define a default operator class for the data type.")));
        return opClassId;
    }

    /*
     * Specific opclass name given, so look up the opclass.
     */

    /* deconstruct the name list */
    DeconstructQualifiedName(opclass, &schemaname, &opcname);

    if (schemaname)
    {
        /* Look in specific schema only */
        Oid         namespaceId;

        namespaceId = LookupExplicitNamespace(schemaname, false);
        tuple = SearchSysCache3(CLAAMNAMENSP,
                                ObjectIdGetDatum(accessMethodId),
                                PointerGetDatum(opcname),
                                ObjectIdGetDatum(namespaceId));
    }
    else
    {
        /* Unqualified opclass name, so search the search path */
        opClassId = OpclassnameGetOpcid(accessMethodId, opcname);
        if (!OidIsValid(opClassId))
            ereport(ERROR,
                    (errcode(ERRCODE_UNDEFINED_OBJECT),
                     errmsg("operator class \"%s\" does not exist for access method \"%s\"",
                            opcname, accessMethodName)));
        tuple = SearchSysCache1(CLAOID, ObjectIdGetDatum(opClassId));
    }

    if (!HeapTupleIsValid(tuple))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_OBJECT),
                 errmsg("operator class \"%s\" does not exist for access method \"%s\"",
                        NameListToString(opclass), accessMethodName)));

    /*
     * Verify that the index operator class accepts this datatype.  Note we
     * will accept binary compatibility.
     */
    opClassId = HeapTupleGetOid(tuple);
    opInputType = ((Form_pg_opclass) GETSTRUCT(tuple))->opcintype;

    if (!IsBinaryCoercible(attrType, opInputType))
        ereport(ERROR,
                (errcode(ERRCODE_DATATYPE_MISMATCH),
                 errmsg("operator class \"%s\" does not accept data type %s",
                      NameListToString(opclass), format_type_be(attrType))));

    ReleaseSysCache(tuple);

    return opClassId;
}

/*
 * GetDefaultOpClass
 *
 * Given the OIDs of a datatype and an access method, find the default
 * operator class, if any.  Returns InvalidOid if there is none.
 */
Oid
GetDefaultOpClass(Oid type_id, Oid am_id)
{
    Oid         result = InvalidOid;
    int         nexact = 0;
    int         ncompatible = 0;
    int         ncompatiblepreferred = 0;
    Relation    rel;
    ScanKeyData skey[1];
    SysScanDesc scan;
    HeapTuple   tup;
    TYPCATEGORY tcategory;

    /* If it's a domain, look at the base type instead */
    type_id = getBaseType(type_id);

    tcategory = TypeCategory(type_id);

    /*
     * We scan through all the opclasses available for the access method,
     * looking for one that is marked default and matches the target type
     * (either exactly or binary-compatibly, but prefer an exact match).
     *
     * We could find more than one binary-compatible match.  If just one is
     * for a preferred type, use that one; otherwise we fail, forcing the user
     * to specify which one he wants.  (The preferred-type special case is a
     * kluge for varchar: it's binary-compatible to both text and bpchar, so
     * we need a tiebreaker.)  If we find more than one exact match, then
     * someone put bogus entries in pg_opclass.
     */
    rel = heap_open(OperatorClassRelationId, AccessShareLock);

    ScanKeyInit(&skey[0],
                Anum_pg_opclass_opcmethod,
                BTEqualStrategyNumber, F_OIDEQ,
                ObjectIdGetDatum(am_id));

    scan = systable_beginscan(rel, OpclassAmNameNspIndexId, true,
                              SnapshotNow, 1, skey);

    while (HeapTupleIsValid(tup = systable_getnext(scan)))
    {
        Form_pg_opclass opclass = (Form_pg_opclass) GETSTRUCT(tup);

        /* ignore altogether if not a default opclass */
        if (!opclass->opcdefault)
            continue;
        if (opclass->opcintype == type_id)
        {
            nexact++;
            result = HeapTupleGetOid(tup);
        }
        else if (nexact == 0 &&
                 IsBinaryCoercible(type_id, opclass->opcintype))
        {
            if (IsPreferredType(tcategory, opclass->opcintype))
            {
                ncompatiblepreferred++;
                result = HeapTupleGetOid(tup);
            }
            else if (ncompatiblepreferred == 0)
            {
                ncompatible++;
                result = HeapTupleGetOid(tup);
            }
        }
    }

    systable_endscan(scan);

    heap_close(rel, AccessShareLock);

    /* raise error if pg_opclass contains inconsistent data */
    if (nexact > 1)
        ereport(ERROR,
                (errcode(ERRCODE_DUPLICATE_OBJECT),
        errmsg("there are multiple default operator classes for data type %s",
               format_type_be(type_id))));

    if (nexact == 1 ||
        ncompatiblepreferred == 1 ||
        (ncompatiblepreferred == 0 && ncompatible == 1))
        return result;

    return InvalidOid;
}

/*
 *  makeObjectName()
 *
 *  Create a name for an implicitly created index, sequence, constraint, etc.
 *
 *  The parameters are typically: the original table name, the original field
 *  name, and a "type" string (such as "seq" or "pkey").    The field name
 *  and/or type can be NULL if not relevant.
 *
 *  The result is a palloc'd string.
 *
 *  The basic result we want is "name1_name2_label", omitting "_name2" or
 *  "_label" when those parameters are NULL.  However, we must generate
 *  a name with less than NAMEDATALEN characters!  So, we truncate one or
 *  both names if necessary to make a short-enough string.  The label part
 *  is never truncated (so it had better be reasonably short).
 *
 *  The caller is responsible for checking uniqueness of the generated
 *  name and retrying as needed; retrying will be done by altering the
 *  "label" string (which is why we never truncate that part).
 */
char *
makeObjectName(const char *name1, const char *name2, const char *label)
{
    char       *name;
    int         overhead = 0;   /* chars needed for label and underscores */
    int         availchars;     /* chars available for name(s) */
    int         name1chars;     /* chars allocated to name1 */
    int         name2chars;     /* chars allocated to name2 */
    int         ndx;

    name1chars = strlen(name1);
    if (name2)
    {
        name2chars = strlen(name2);
        overhead++;             /* allow for separating underscore */
    }
    else
        name2chars = 0;
    if (label)
        overhead += strlen(label) + 1;

    availchars = NAMEDATALEN - 1 - overhead;
    Assert(availchars > 0);     /* else caller chose a bad label */

    /*
     * If we must truncate,  preferentially truncate the longer name. This
     * logic could be expressed without a loop, but it's simple and obvious as
     * a loop.
     */
    while (name1chars + name2chars > availchars)
    {
        if (name1chars > name2chars)
            name1chars--;
        else
            name2chars--;
    }

    name1chars = pg_mbcliplen(name1, name1chars, name1chars);
    if (name2)
        name2chars = pg_mbcliplen(name2, name2chars, name2chars);

    /* Now construct the string using the chosen lengths */
    name = palloc(name1chars + name2chars + overhead + 1);
    memcpy(name, name1, name1chars);
    ndx = name1chars;
    if (name2)
    {
        name[ndx++] = '_';
        memcpy(name + ndx, name2, name2chars);
        ndx += name2chars;
    }
    if (label)
    {
        name[ndx++] = '_';
        strcpy(name + ndx, label);
    }
    else
        name[ndx] = '\0';

    return name;
}

/*
 * Select a nonconflicting name for a new relation.  This is ordinarily
 * used to choose index names (which is why it's here) but it can also
 * be used for sequences, or any autogenerated relation kind.
 *
 * name1, name2, and label are used the same way as for makeObjectName(),
 * except that the label can't be NULL; digits will be appended to the label
 * if needed to create a name that is unique within the specified namespace.
 *
 * Note: it is theoretically possible to get a collision anyway, if someone
 * else chooses the same name concurrently.  This is fairly unlikely to be
 * a problem in practice, especially if one is holding an exclusive lock on
 * the relation identified by name1.  However, if choosing multiple names
 * within a single command, you'd better create the new object and do
 * CommandCounterIncrement before choosing the next one!
 *
 * Returns a palloc'd string.
 */
char *
ChooseRelationName(const char *name1, const char *name2,
                   const char *label, Oid namespaceid)
{
    int         pass = 0;
    char       *relname = NULL;
    char        modlabel[NAMEDATALEN];

    /* try the unmodified label first */
    StrNCpy(modlabel, label, sizeof(modlabel));

    for (;;)
    {
        relname = makeObjectName(name1, name2, modlabel);

        if (!OidIsValid(get_relname_relid(relname, namespaceid)))
            break;

        /* found a conflict, so try a new name component */
        pfree(relname);
        snprintf(modlabel, sizeof(modlabel), "%s%d", label, ++pass);
    }

    return relname;
}

/*
 * Select the name to be used for an index.
 *
 * The argument list is pretty ad-hoc :-(
 */
static char *
ChooseIndexName(const char *tabname, Oid namespaceId,
                List *colnames, List *exclusionOpNames,
                bool primary, bool isconstraint)
{
    char       *indexname;

    if (primary)
    {
        /* the primary key's name does not depend on the specific column(s) */
        indexname = ChooseRelationName(tabname,
                                       NULL,
                                       "pkey",
                                       namespaceId);
    }
    else if (exclusionOpNames != NIL)
    {
        indexname = ChooseRelationName(tabname,
                                       ChooseIndexNameAddition(colnames),
                                       "excl",
                                       namespaceId);
    }
    else if (isconstraint)
    {
        indexname = ChooseRelationName(tabname,
                                       ChooseIndexNameAddition(colnames),
                                       "key",
                                       namespaceId);
    }
    else
    {
        indexname = ChooseRelationName(tabname,
                                       ChooseIndexNameAddition(colnames),
                                       "idx",
                                       namespaceId);
    }

    return indexname;
}

/*
 * Generate "name2" for a new index given the list of column names for it
 * (as produced by ChooseIndexColumnNames).  This will be passed to
 * ChooseRelationName along with the parent table name and a suitable label.
 *
 * We know that less than NAMEDATALEN characters will actually be used,
 * so we can truncate the result once we've generated that many.
 */
static char *
ChooseIndexNameAddition(List *colnames)
{
    char        buf[NAMEDATALEN * 2];
    int         buflen = 0;
    ListCell   *lc;

    buf[0] = '\0';
    foreach(lc, colnames)
    {
        const char *name = (const char *) lfirst(lc);

        if (buflen > 0)
            buf[buflen++] = '_';    /* insert _ between names */

        /*
         * At this point we have buflen <= NAMEDATALEN.  name should be less
         * than NAMEDATALEN already, but use strlcpy for paranoia.
         */
        strlcpy(buf + buflen, name, NAMEDATALEN);
        buflen += strlen(buf + buflen);
        if (buflen >= NAMEDATALEN)
            break;
    }
    return pstrdup(buf);
}

/*
 * Select the actual names to be used for the columns of an index, given the
 * list of IndexElems for the columns.  This is mostly about ensuring the
 * names are unique so we don't get a conflicting-attribute-names error.
 *
 * Returns a List of plain strings (char *, not String nodes).
 */
static List *
ChooseIndexColumnNames(List *indexElems)
{
    List       *result = NIL;
    ListCell   *lc;

    foreach(lc, indexElems)
    {
        IndexElem  *ielem = (IndexElem *) lfirst(lc);
        const char *origname;
        const char *curname;
        int         i;
        char        buf[NAMEDATALEN];

        /* Get the preliminary name from the IndexElem */
        if (ielem->indexcolname)
            origname = ielem->indexcolname;     /* caller-specified name */
        else if (ielem->name)
            origname = ielem->name;     /* simple column reference */
        else
            origname = "expr";  /* default name for expression */

        /* If it conflicts with any previous column, tweak it */
        curname = origname;
        for (i = 1;; i++)
        {
            ListCell   *lc2;
            char        nbuf[32];
            int         nlen;

            foreach(lc2, result)
            {
                if (strcmp(curname, (char *) lfirst(lc2)) == 0)
                    break;
            }
            if (lc2 == NULL)
                break;          /* found nonconflicting name */

            sprintf(nbuf, "%d", i);

            /* Ensure generated names are shorter than NAMEDATALEN */
            nlen = pg_mbcliplen(origname, strlen(origname),
                                NAMEDATALEN - 1 - strlen(nbuf));
            memcpy(buf, origname, nlen);
            strcpy(buf + nlen, nbuf);
            curname = buf;
        }

        /* And attach to the result list */
        result = lappend(result, pstrdup(curname));
    }
    return result;
}

/*
 * ReindexIndex
 *      Recreate a specific index.
 */
Oid
ReindexIndex(RangeVar *indexRelation)
{
    Oid         indOid;
    Oid         heapOid = InvalidOid;

    /* lock level used here should match index lock reindex_index() */
    indOid = RangeVarGetRelidExtended(indexRelation, AccessExclusiveLock,
                                      false, false,
                                      RangeVarCallbackForReindexIndex,
                                      (void *) &heapOid);

    reindex_index(indOid, false);

    return indOid;
}

/*
 * Check permissions on table before acquiring relation lock; also lock
 * the heap before the RangeVarGetRelidExtended takes the index lock, to avoid
 * deadlocks.
 */
static void
RangeVarCallbackForReindexIndex(const RangeVar *relation,
                                Oid relId, Oid oldRelId, void *arg)
{
    char        relkind;
    Oid        *heapOid = (Oid *) arg;

    /*
     * 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 (relId != oldRelId && OidIsValid(oldRelId))
    {
        /* lock level here should match reindex_index() heap lock */
        UnlockRelationOid(*heapOid, ShareLock);
        *heapOid = InvalidOid;
    }

    /* If the relation does not exist, there's nothing more to do. */
    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_INDEX)
        ereport(ERROR,
                (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                 errmsg("\"%s\" is not an index", relation->relname)));

    /* Check permissions */
    if (!pg_class_ownercheck(relId, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS, relation->relname);

    /* Lock heap before index to avoid deadlock. */
    if (relId != oldRelId)
    {
        /*
         * Lock level here should match reindex_index() heap lock. If the OID
         * isn't valid, it means the index as concurrently dropped, which is
         * not a problem for us; just return normally.
         */
        *heapOid = IndexGetRelation(relId, true);
        if (OidIsValid(*heapOid))
            LockRelationOid(*heapOid, ShareLock);
    }
}

/*
 * ReindexTable
 *      Recreate all indexes of a table (and of its toast table, if any)
 */
Oid
ReindexTable(RangeVar *relation)
{
    Oid         heapOid;

    /* The lock level used here should match reindex_relation(). */
    heapOid = RangeVarGetRelidExtended(relation, ShareLock, false, false,
                                       RangeVarCallbackOwnsTable, NULL);

    if (!reindex_relation(heapOid, REINDEX_REL_PROCESS_TOAST))
        ereport(NOTICE,
                (errmsg("table \"%s\" has no indexes",
                        relation->relname)));

    return heapOid;
}

/*
 * ReindexDatabase
 *      Recreate indexes of a database.
 *
 * To reduce the probability of deadlocks, each table is reindexed in a
 * separate transaction, so we can release the lock on it right away.
 * That means this must not be called within a user transaction block!
 */
Oid
ReindexDatabase(const char *databaseName, bool do_system, bool do_user)
{
    Relation    relationRelation;
    HeapScanDesc scan;
    HeapTuple   tuple;
    MemoryContext private_context;
    MemoryContext old;
    List       *relids = NIL;
    ListCell   *l;

    AssertArg(databaseName);

    if (strcmp(databaseName, get_database_name(MyDatabaseId)) != 0)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("can only reindex the currently open database")));

    if (!pg_database_ownercheck(MyDatabaseId, GetUserId()))
        aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_DATABASE,
                       databaseName);

    /*
     * Create a memory context that will survive forced transaction commits we
     * do below.  Since it is a child of PortalContext, it will go away
     * eventually even if we suffer an error; there's no need for special
     * abort cleanup logic.
     */
    private_context = AllocSetContextCreate(PortalContext,
                                            "ReindexDatabase",
                                            ALLOCSET_DEFAULT_MINSIZE,
                                            ALLOCSET_DEFAULT_INITSIZE,
                                            ALLOCSET_DEFAULT_MAXSIZE);

    /*
     * We always want to reindex pg_class first.  This ensures that if there
     * is any corruption in pg_class' indexes, they will be fixed before we
     * process any other tables.  This is critical because reindexing itself
     * will try to update pg_class.
     */
    if (do_system)
    {
        old = MemoryContextSwitchTo(private_context);
        relids = lappend_oid(relids, RelationRelationId);
        MemoryContextSwitchTo(old);
    }

    /*
     * Scan pg_class to build a list of the relations we need to reindex.
     *
     * We only consider plain relations here (toast rels will be processed
     * indirectly by reindex_relation).
     */
    relationRelation = heap_open(RelationRelationId, AccessShareLock);
    scan = heap_beginscan(relationRelation, SnapshotNow, 0, NULL);
    while ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
    {
        Form_pg_class classtuple = (Form_pg_class) GETSTRUCT(tuple);

        if (classtuple->relkind != RELKIND_RELATION &&
            classtuple->relkind != RELKIND_MATVIEW)
            continue;

        /* Skip temp tables of other backends; we can't reindex them at all */
        if (classtuple->relpersistence == RELPERSISTENCE_TEMP &&
            !isTempNamespace(classtuple->relnamespace))
            continue;

        /* Check user/system classification, and optionally skip */
        if (IsSystemClass(classtuple))
        {
            if (!do_system)
                continue;
        }
        else
        {
            if (!do_user)
                continue;
        }

        if (HeapTupleGetOid(tuple) == RelationRelationId)
            continue;           /* got it already */

        old = MemoryContextSwitchTo(private_context);
        relids = lappend_oid(relids, HeapTupleGetOid(tuple));
        MemoryContextSwitchTo(old);
    }
    heap_endscan(scan);
    heap_close(relationRelation, AccessShareLock);

    /* Now reindex each rel in a separate transaction */
    PopActiveSnapshot();
    CommitTransactionCommand();
    foreach(l, relids)
    {
        Oid         relid = lfirst_oid(l);

        StartTransactionCommand();
        /* functions in indexes may want a snapshot set */
        PushActiveSnapshot(GetTransactionSnapshot());
        if (reindex_relation(relid, REINDEX_REL_PROCESS_TOAST))
            ereport(NOTICE,
                    (errmsg("table \"%s.%s\" was reindexed",
                            get_namespace_name(get_rel_namespace(relid)),
                            get_rel_name(relid))));
        PopActiveSnapshot();
        CommitTransactionCommand();
    }
    StartTransactionCommand();

    MemoryContextDelete(private_context);

    return MyDatabaseId;
}