relation.h

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * relation.h
 *    Definitions for planner's internal data structures.
 *
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * src/include/nodes/relation.h
 *
 *-------------------------------------------------------------------------
 */
#ifndef RELATION_H
#define RELATION_H

#include "access/sdir.h"
#include "nodes/params.h"
#include "nodes/parsenodes.h"
#include "storage/block.h"


/*
 * Relids
 *      Set of relation identifiers (indexes into the rangetable).
 */
typedef Bitmapset *Relids;

/*
 * When looking for a "cheapest path", this enum specifies whether we want
 * cheapest startup cost or cheapest total cost.
 */
typedef enum CostSelector
{
    STARTUP_COST, TOTAL_COST
} CostSelector;

/*
 * The cost estimate produced by cost_qual_eval() includes both a one-time
 * (startup) cost, and a per-tuple cost.
 */
typedef struct QualCost
{
    Cost        startup;        /* one-time cost */
    Cost        per_tuple;      /* per-evaluation cost */
} QualCost;

/*
 * Costing aggregate function execution requires these statistics about
 * the aggregates to be executed by a given Agg node.  Note that transCost
 * includes the execution costs of the aggregates' input expressions.
 */
typedef struct AggClauseCosts
{
    int         numAggs;        /* total number of aggregate functions */
    int         numOrderedAggs; /* number that use DISTINCT or ORDER BY */
    QualCost    transCost;      /* total per-input-row execution costs */
    Cost        finalCost;      /* total costs of agg final functions */
    Size        transitionSpace;    /* space for pass-by-ref transition data */
} AggClauseCosts;


/*----------
 * PlannerGlobal
 *      Global information for planning/optimization
 *
 * PlannerGlobal holds state for an entire planner invocation; this state
 * is shared across all levels of sub-Queries that exist in the command being
 * planned.
 *----------
 */
typedef struct PlannerGlobal
{
    NodeTag     type;

    ParamListInfo boundParams;  /* Param values provided to planner() */

    List       *subplans;       /* Plans for SubPlan nodes */

    List       *subroots;       /* PlannerInfos for SubPlan nodes */

    Bitmapset  *rewindPlanIDs;  /* indices of subplans that require REWIND */

    List       *finalrtable;    /* "flat" rangetable for executor */

    List       *finalrowmarks;  /* "flat" list of PlanRowMarks */

    List       *resultRelations;    /* "flat" list of integer RT indexes */

    List       *relationOids;   /* OIDs of relations the plan depends on */

    List       *invalItems;     /* other dependencies, as PlanInvalItems */

    int         nParamExec;     /* number of PARAM_EXEC Params used */

    Index       lastPHId;       /* highest PlaceHolderVar ID assigned */

    Index       lastRowMarkId;  /* highest PlanRowMark ID assigned */

    bool        transientPlan;  /* redo plan when TransactionXmin changes? */
} PlannerGlobal;

/* macro for fetching the Plan associated with a SubPlan node */
#define planner_subplan_get_plan(root, subplan) \
    ((Plan *) list_nth((root)->glob->subplans, (subplan)->plan_id - 1))


/*----------
 * PlannerInfo
 *      Per-query information for planning/optimization
 *
 * This struct is conventionally called "root" in all the planner routines.
 * It holds links to all of the planner's working state, in addition to the
 * original Query.  Note that at present the planner extensively modifies
 * the passed-in Query data structure; someday that should stop.
 *----------
 */
typedef struct PlannerInfo
{
    NodeTag     type;

    Query      *parse;          /* the Query being planned */

    PlannerGlobal *glob;        /* global info for current planner run */

    Index       query_level;    /* 1 at the outermost Query */

    struct PlannerInfo *parent_root;    /* NULL at outermost Query */

    List       *plan_params;    /* list of PlannerParamItems, see below */

    /*
     * simple_rel_array holds pointers to "base rels" and "other rels" (see
     * comments for RelOptInfo for more info).  It is indexed by rangetable
     * index (so entry 0 is always wasted).  Entries can be NULL when an RTE
     * does not correspond to a base relation, such as a join RTE or an
     * unreferenced view RTE; or if the RelOptInfo hasn't been made yet.
     */
    struct RelOptInfo **simple_rel_array;       /* All 1-rel RelOptInfos */
    int         simple_rel_array_size;  /* allocated size of array */

    /*
     * simple_rte_array is the same length as simple_rel_array and holds
     * pointers to the associated rangetable entries.  This lets us avoid
     * rt_fetch(), which can be a bit slow once large inheritance sets have
     * been expanded.
     */
    RangeTblEntry **simple_rte_array;   /* rangetable as an array */

    /*
     * all_baserels is a Relids set of all base relids (but not "other"
     * relids) in the query; that is, the Relids identifier of the final join
     * we need to form.
     */
    Relids      all_baserels;

    /*
     * join_rel_list is a list of all join-relation RelOptInfos we have
     * considered in this planning run.  For small problems we just scan the
     * list to do lookups, but when there are many join relations we build a
     * hash table for faster lookups.  The hash table is present and valid
     * when join_rel_hash is not NULL.  Note that we still maintain the list
     * even when using the hash table for lookups; this simplifies life for
     * GEQO.
     */
    List       *join_rel_list;  /* list of join-relation RelOptInfos */
    struct HTAB *join_rel_hash; /* optional hashtable for join relations */

    /*
     * When doing a dynamic-programming-style join search, join_rel_level[k]
     * is a list of all join-relation RelOptInfos of level k, and
     * join_cur_level is the current level.  New join-relation RelOptInfos are
     * automatically added to the join_rel_level[join_cur_level] list.
     * join_rel_level is NULL if not in use.
     */
    List      **join_rel_level; /* lists of join-relation RelOptInfos */
    int         join_cur_level; /* index of list being extended */

    List       *init_plans;     /* init SubPlans for query */

    List       *cte_plan_ids;   /* per-CTE-item list of subplan IDs */

    List       *eq_classes;     /* list of active EquivalenceClasses */

    List       *canon_pathkeys; /* list of "canonical" PathKeys */

    List       *left_join_clauses;      /* list of RestrictInfos for
                                         * mergejoinable outer join clauses
                                         * w/nonnullable var on left */

    List       *right_join_clauses;     /* list of RestrictInfos for
                                         * mergejoinable outer join clauses
                                         * w/nonnullable var on right */

    List       *full_join_clauses;      /* list of RestrictInfos for
                                         * mergejoinable full join clauses */

    List       *join_info_list;     /* list of SpecialJoinInfos */

    List       *lateral_info_list;  /* list of LateralJoinInfos */

    List       *append_rel_list;    /* list of AppendRelInfos */

    List       *rowMarks;       /* list of PlanRowMarks */

    List       *placeholder_list;       /* list of PlaceHolderInfos */

    List       *query_pathkeys; /* desired pathkeys for query_planner(), and
                                 * actual pathkeys after planning */

    List       *group_pathkeys; /* groupClause pathkeys, if any */
    List       *window_pathkeys;    /* pathkeys of bottom window, if any */
    List       *distinct_pathkeys;      /* distinctClause pathkeys, if any */
    List       *sort_pathkeys;  /* sortClause pathkeys, if any */

    List       *minmax_aggs;    /* List of MinMaxAggInfos */

    List       *initial_rels;   /* RelOptInfos we are now trying to join */

    MemoryContext planner_cxt;  /* context holding PlannerInfo */

    double      total_table_pages;      /* # of pages in all tables of query */

    double      tuple_fraction; /* tuple_fraction passed to query_planner */
    double      limit_tuples;   /* limit_tuples passed to query_planner */

    bool        hasInheritedTarget;     /* true if parse->resultRelation is an
                                         * inheritance child rel */
    bool        hasJoinRTEs;    /* true if any RTEs are RTE_JOIN kind */
    bool        hasLateralRTEs; /* true if any RTEs are marked LATERAL */
    bool        hasHavingQual;  /* true if havingQual was non-null */
    bool        hasPseudoConstantQuals; /* true if any RestrictInfo has
                                         * pseudoconstant = true */
    bool        hasRecursion;   /* true if planning a recursive WITH item */

    /* These fields are used only when hasRecursion is true: */
    int         wt_param_id;    /* PARAM_EXEC ID for the work table */
    struct Plan *non_recursive_plan;    /* plan for non-recursive term */

    /* These fields are workspace for createplan.c */
    Relids      curOuterRels;   /* outer rels above current node */
    List       *curOuterParams; /* not-yet-assigned NestLoopParams */

    /* optional private data for join_search_hook, e.g., GEQO */
    void       *join_search_private;
} PlannerInfo;


/*
 * In places where it's known that simple_rte_array[] must have been prepared
 * already, we just index into it to fetch RTEs.  In code that might be
 * executed before or after entering query_planner(), use this macro.
 */
#define planner_rt_fetch(rti, root) \
    ((root)->simple_rte_array ? (root)->simple_rte_array[rti] : \
     rt_fetch(rti, (root)->parse->rtable))


/*----------
 * RelOptInfo
 *      Per-relation information for planning/optimization
 *
 * For planning purposes, a "base rel" is either a plain relation (a table)
 * or the output of a sub-SELECT or function that appears in the range table.
 * In either case it is uniquely identified by an RT index.  A "joinrel"
 * is the joining of two or more base rels.  A joinrel is identified by
 * the set of RT indexes for its component baserels.  We create RelOptInfo
 * nodes for each baserel and joinrel, and store them in the PlannerInfo's
 * simple_rel_array and join_rel_list respectively.
 *
 * Note that there is only one joinrel for any given set of component
 * baserels, no matter what order we assemble them in; so an unordered
 * set is the right datatype to identify it with.
 *
 * We also have "other rels", which are like base rels in that they refer to
 * single RT indexes; but they are not part of the join tree, and are given
 * a different RelOptKind to identify them.  Lastly, there is a RelOptKind
 * for "dead" relations, which are base rels that we have proven we don't
 * need to join after all.
 *
 * Currently the only kind of otherrels are those made for member relations
 * of an "append relation", that is an inheritance set or UNION ALL subquery.
 * An append relation has a parent RTE that is a base rel, which represents
 * the entire append relation.  The member RTEs are otherrels.  The parent
 * is present in the query join tree but the members are not.  The member
 * RTEs and otherrels are used to plan the scans of the individual tables or
 * subqueries of the append set; then the parent baserel is given Append
 * and/or MergeAppend paths comprising the best paths for the individual
 * member rels.  (See comments for AppendRelInfo for more information.)
 *
 * At one time we also made otherrels to represent join RTEs, for use in
 * handling join alias Vars.  Currently this is not needed because all join
 * alias Vars are expanded to non-aliased form during preprocess_expression.
 *
 * Parts of this data structure are specific to various scan and join
 * mechanisms.  It didn't seem worth creating new node types for them.
 *
 *      relids - Set of base-relation identifiers; it is a base relation
 *              if there is just one, a join relation if more than one
 *      rows - estimated number of tuples in the relation after restriction
 *             clauses have been applied (ie, output rows of a plan for it)
 *      width - avg. number of bytes per tuple in the relation after the
 *              appropriate projections have been done (ie, output width)
 *      consider_startup - true if there is any value in keeping paths for
 *                         this rel on the basis of having cheap startup cost
 *      reltargetlist - List of Var and PlaceHolderVar nodes for the values
 *                      we need to output from this relation.
 *                      List is in no particular order, but all rels of an
 *                      appendrel set must use corresponding orders.
 *                      NOTE: in an appendrel child relation, may contain
 *                      arbitrary expressions pulled up from a subquery!
 *      pathlist - List of Path nodes, one for each potentially useful
 *                 method of generating the relation
 *      ppilist - ParamPathInfo nodes for parameterized Paths, if any
 *      cheapest_startup_path - the pathlist member with lowest startup cost
 *          (regardless of ordering) among the unparameterized paths;
 *          or NULL if there is no unparameterized path
 *      cheapest_total_path - the pathlist member with lowest total cost
 *          (regardless of ordering) among the unparameterized paths;
 *          or if there is no unparameterized path, the path with lowest
 *          total cost among the paths with minimum parameterization
 *      cheapest_unique_path - for caching cheapest path to produce unique
 *          (no duplicates) output from relation; NULL if not yet requested
 *      cheapest_parameterized_paths - best paths for their parameterizations;
 *          always includes cheapest_total_path, even if that's unparameterized
 *
 * If the relation is a base relation it will have these fields set:
 *
 *      relid - RTE index (this is redundant with the relids field, but
 *              is provided for convenience of access)
 *      rtekind - distinguishes plain relation, subquery, or function RTE
 *      min_attr, max_attr - range of valid AttrNumbers for rel
 *      attr_needed - array of bitmapsets indicating the highest joinrel
 *              in which each attribute is needed; if bit 0 is set then
 *              the attribute is needed as part of final targetlist
 *      attr_widths - cache space for per-attribute width estimates;
 *                    zero means not computed yet
 *      lateral_vars - lateral cross-references of rel, if any (list of
 *                     Vars and PlaceHolderVars)
 *      lateral_relids - required outer rels for LATERAL, as a Relids set
 *                       (for child rels this can be more than lateral_vars)
 *      indexlist - list of IndexOptInfo nodes for relation's indexes
 *                  (always NIL if it's not a table)
 *      pages - number of disk pages in relation (zero if not a table)
 *      tuples - number of tuples in relation (not considering restrictions)
 *      allvisfrac - fraction of disk pages that are marked all-visible
 *      subplan - plan for subquery (NULL if it's not a subquery)
 *      subroot - PlannerInfo for subquery (NULL if it's not a subquery)
 *      subplan_params - list of PlannerParamItems to be passed to subquery
 *      fdwroutine - function hooks for FDW, if foreign table (else NULL)
 *      fdw_private - private state for FDW, if foreign table (else NULL)
 *
 *      Note: for a subquery, tuples, subplan, subroot are not set immediately
 *      upon creation of the RelOptInfo object; they are filled in when
 *      set_subquery_pathlist processes the object.  Likewise, fdwroutine
 *      and fdw_private are filled during initial path creation.
 *
 *      For otherrels that are appendrel members, these fields are filled
 *      in just as for a baserel.
 *
 * The presence of the remaining fields depends on the restrictions
 * and joins that the relation participates in:
 *
 *      baserestrictinfo - List of RestrictInfo nodes, containing info about
 *                  each non-join qualification clause in which this relation
 *                  participates (only used for base rels)
 *      baserestrictcost - Estimated cost of evaluating the baserestrictinfo
 *                  clauses at a single tuple (only used for base rels)
 *      joininfo  - List of RestrictInfo nodes, containing info about each
 *                  join clause in which this relation participates (but
 *                  note this excludes clauses that might be derivable from
 *                  EquivalenceClasses)
 *      has_eclass_joins - flag that EquivalenceClass joins are possible
 *
 * Note: Keeping a restrictinfo list in the RelOptInfo is useful only for
 * base rels, because for a join rel the set of clauses that are treated as
 * restrict clauses varies depending on which sub-relations we choose to join.
 * (For example, in a 3-base-rel join, a clause relating rels 1 and 2 must be
 * treated as a restrictclause if we join {1} and {2 3} to make {1 2 3}; but
 * if we join {1 2} and {3} then that clause will be a restrictclause in {1 2}
 * and should not be processed again at the level of {1 2 3}.)  Therefore,
 * the restrictinfo list in the join case appears in individual JoinPaths
 * (field joinrestrictinfo), not in the parent relation.  But it's OK for
 * the RelOptInfo to store the joininfo list, because that is the same
 * for a given rel no matter how we form it.
 *
 * We store baserestrictcost in the RelOptInfo (for base relations) because
 * we know we will need it at least once (to price the sequential scan)
 * and may need it multiple times to price index scans.
 *----------
 */
typedef enum RelOptKind
{
    RELOPT_BASEREL,
    RELOPT_JOINREL,
    RELOPT_OTHER_MEMBER_REL,
    RELOPT_DEADREL
} RelOptKind;

typedef struct RelOptInfo
{
    NodeTag     type;

    RelOptKind  reloptkind;

    /* all relations included in this RelOptInfo */
    Relids      relids;         /* set of base relids (rangetable indexes) */

    /* size estimates generated by planner */
    double      rows;           /* estimated number of result tuples */
    int         width;          /* estimated avg width of result tuples */

    /* per-relation planner control flags */
    bool        consider_startup;   /* keep cheap-startup-cost paths? */

    /* materialization information */
    List       *reltargetlist;  /* Vars to be output by scan of relation */
    List       *pathlist;       /* Path structures */
    List       *ppilist;        /* ParamPathInfos used in pathlist */
    struct Path *cheapest_startup_path;
    struct Path *cheapest_total_path;
    struct Path *cheapest_unique_path;
    List       *cheapest_parameterized_paths;

    /* information about a base rel (not set for join rels!) */
    Index       relid;
    Oid         reltablespace;  /* containing tablespace */
    RTEKind     rtekind;        /* RELATION, SUBQUERY, or FUNCTION */
    AttrNumber  min_attr;       /* smallest attrno of rel (often <0) */
    AttrNumber  max_attr;       /* largest attrno of rel */
    Relids     *attr_needed;    /* array indexed [min_attr .. max_attr] */
    int32      *attr_widths;    /* array indexed [min_attr .. max_attr] */
    List       *lateral_vars;   /* LATERAL Vars and PHVs referenced by rel */
    Relids      lateral_relids; /* minimum parameterization of rel */
    List       *indexlist;      /* list of IndexOptInfo */
    BlockNumber pages;          /* size estimates derived from pg_class */
    double      tuples;
    double      allvisfrac;
    /* use "struct Plan" to avoid including plannodes.h here */
    struct Plan *subplan;       /* if subquery */
    PlannerInfo *subroot;       /* if subquery */
    List       *subplan_params; /* if subquery */
    /* use "struct FdwRoutine" to avoid including fdwapi.h here */
    struct FdwRoutine *fdwroutine;      /* if foreign table */
    void       *fdw_private;    /* if foreign table */

    /* used by various scans and joins: */
    List       *baserestrictinfo;       /* RestrictInfo structures (if base
                                         * rel) */
    QualCost    baserestrictcost;       /* cost of evaluating the above */
    List       *joininfo;       /* RestrictInfo structures for join clauses
                                 * involving this rel */
    bool        has_eclass_joins;       /* T means joininfo is incomplete */
} RelOptInfo;

/*
 * IndexOptInfo
 *      Per-index information for planning/optimization
 *
 *      indexkeys[], indexcollations[], opfamily[], and opcintype[]
 *      each have ncolumns entries.
 *
 *      sortopfamily[], reverse_sort[], and nulls_first[] likewise have
 *      ncolumns entries, if the index is ordered; but if it is unordered,
 *      those pointers are NULL.
 *
 *      Zeroes in the indexkeys[] array indicate index columns that are
 *      expressions; there is one element in indexprs for each such column.
 *
 *      For an ordered index, reverse_sort[] and nulls_first[] describe the
 *      sort ordering of a forward indexscan; we can also consider a backward
 *      indexscan, which will generate the reverse ordering.
 *
 *      The indexprs and indpred expressions have been run through
 *      prepqual.c and eval_const_expressions() for ease of matching to
 *      WHERE clauses. indpred is in implicit-AND form.
 *
 *      indextlist is a TargetEntry list representing the index columns.
 *      It provides an equivalent base-relation Var for each simple column,
 *      and links to the matching indexprs element for each expression column.
 */
typedef struct IndexOptInfo
{
    NodeTag     type;

    Oid         indexoid;       /* OID of the index relation */
    Oid         reltablespace;  /* tablespace of index (not table) */
    RelOptInfo *rel;            /* back-link to index's table */

    /* index-size statistics (from pg_class and elsewhere) */
    BlockNumber pages;          /* number of disk pages in index */
    double      tuples;         /* number of index tuples in index */
    int         tree_height;    /* index tree height, or -1 if unknown */

    /* index descriptor information */
    int         ncolumns;       /* number of columns in index */
    int        *indexkeys;      /* column numbers of index's keys, or 0 */
    Oid        *indexcollations;    /* OIDs of collations of index columns */
    Oid        *opfamily;       /* OIDs of operator families for columns */
    Oid        *opcintype;      /* OIDs of opclass declared input data types */
    Oid        *sortopfamily;   /* OIDs of btree opfamilies, if orderable */
    bool       *reverse_sort;   /* is sort order descending? */
    bool       *nulls_first;    /* do NULLs come first in the sort order? */
    Oid         relam;          /* OID of the access method (in pg_am) */

    RegProcedure amcostestimate;    /* OID of the access method's cost fcn */

    List       *indexprs;       /* expressions for non-simple index columns */
    List       *indpred;        /* predicate if a partial index, else NIL */

    List       *indextlist;     /* targetlist representing index columns */

    bool        predOK;         /* true if predicate matches query */
    bool        unique;         /* true if a unique index */
    bool        immediate;      /* is uniqueness enforced immediately? */
    bool        hypothetical;   /* true if index doesn't really exist */
    bool        canreturn;      /* can index return IndexTuples? */
    bool        amcanorderbyop; /* does AM support order by operator result? */
    bool        amoptionalkey;  /* can query omit key for the first column? */
    bool        amsearcharray;  /* can AM handle ScalarArrayOpExpr quals? */
    bool        amsearchnulls;  /* can AM search for NULL/NOT NULL entries? */
    bool        amhasgettuple;  /* does AM have amgettuple interface? */
    bool        amhasgetbitmap; /* does AM have amgetbitmap interface? */
} IndexOptInfo;


/*
 * EquivalenceClasses
 *
 * Whenever we can determine that a mergejoinable equality clause A = B is
 * not delayed by any outer join, we create an EquivalenceClass containing
 * the expressions A and B to record this knowledge.  If we later find another
 * equivalence B = C, we add C to the existing EquivalenceClass; this may
 * require merging two existing EquivalenceClasses.  At the end of the qual
 * distribution process, we have sets of values that are known all transitively
 * equal to each other, where "equal" is according to the rules of the btree
 * operator family(s) shown in ec_opfamilies, as well as the collation shown
 * by ec_collation.  (We restrict an EC to contain only equalities whose
 * operators belong to the same set of opfamilies.  This could probably be
 * relaxed, but for now it's not worth the trouble, since nearly all equality
 * operators belong to only one btree opclass anyway.  Similarly, we suppose
 * that all or none of the input datatypes are collatable, so that a single
 * collation value is sufficient.)
 *
 * We also use EquivalenceClasses as the base structure for PathKeys, letting
 * us represent knowledge about different sort orderings being equivalent.
 * Since every PathKey must reference an EquivalenceClass, we will end up
 * with single-member EquivalenceClasses whenever a sort key expression has
 * not been equivalenced to anything else.  It is also possible that such an
 * EquivalenceClass will contain a volatile expression ("ORDER BY random()"),
 * which is a case that can't arise otherwise since clauses containing
 * volatile functions are never considered mergejoinable.  We mark such
 * EquivalenceClasses specially to prevent them from being merged with
 * ordinary EquivalenceClasses.  Also, for volatile expressions we have
 * to be careful to match the EquivalenceClass to the correct targetlist
 * entry: consider SELECT random() AS a, random() AS b ... ORDER BY b,a.
 * So we record the SortGroupRef of the originating sort clause.
 *
 * We allow equality clauses appearing below the nullable side of an outer join
 * to form EquivalenceClasses, but these have a slightly different meaning:
 * the included values might be all NULL rather than all the same non-null
 * values.  See src/backend/optimizer/README for more on that point.
 *
 * NB: if ec_merged isn't NULL, this class has been merged into another, and
 * should be ignored in favor of using the pointed-to class.
 */
typedef struct EquivalenceClass
{
    NodeTag     type;

    List       *ec_opfamilies;  /* btree operator family OIDs */
    Oid         ec_collation;   /* collation, if datatypes are collatable */
    List       *ec_members;     /* list of EquivalenceMembers */
    List       *ec_sources;     /* list of generating RestrictInfos */
    List       *ec_derives;     /* list of derived RestrictInfos */
    Relids      ec_relids;      /* all relids appearing in ec_members */
    bool        ec_has_const;   /* any pseudoconstants in ec_members? */
    bool        ec_has_volatile;    /* the (sole) member is a volatile expr */
    bool        ec_below_outer_join;    /* equivalence applies below an OJ */
    bool        ec_broken;      /* failed to generate needed clauses? */
    Index       ec_sortref;     /* originating sortclause label, or 0 */
    struct EquivalenceClass *ec_merged; /* set if merged into another EC */
} EquivalenceClass;

/*
 * If an EC contains a const and isn't below-outer-join, any PathKey depending
 * on it must be redundant, since there's only one possible value of the key.
 */
#define EC_MUST_BE_REDUNDANT(eclass)  \
    ((eclass)->ec_has_const && !(eclass)->ec_below_outer_join)

/*
 * EquivalenceMember - one member expression of an EquivalenceClass
 *
 * em_is_child signifies that this element was built by transposing a member
 * for an appendrel parent relation to represent the corresponding expression
 * for an appendrel child.  These members are used for determining the
 * pathkeys of scans on the child relation and for explicitly sorting the
 * child when necessary to build a MergeAppend path for the whole appendrel
 * tree.  An em_is_child member has no impact on the properties of the EC as a
 * whole; in particular the EC's ec_relids field does NOT include the child
 * relation.  An em_is_child member should never be marked em_is_const nor
 * cause ec_has_const or ec_has_volatile to be set, either.  Thus, em_is_child
 * members are not really full-fledged members of the EC, but just reflections
 * or doppelgangers of real members.  Most operations on EquivalenceClasses
 * should ignore em_is_child members, and those that don't should test
 * em_relids to make sure they only consider relevant members.
 *
 * em_datatype is usually the same as exprType(em_expr), but can be
 * different when dealing with a binary-compatible opfamily; in particular
 * anyarray_ops would never work without this.  Use em_datatype when
 * looking up a specific btree operator to work with this expression.
 */
typedef struct EquivalenceMember
{
    NodeTag     type;

    Expr       *em_expr;        /* the expression represented */
    Relids      em_relids;      /* all relids appearing in em_expr */
    Relids      em_nullable_relids;     /* nullable by lower outer joins */
    bool        em_is_const;    /* expression is pseudoconstant? */
    bool        em_is_child;    /* derived version for a child relation? */
    Oid         em_datatype;    /* the "nominal type" used by the opfamily */
} EquivalenceMember;

/*
 * PathKeys
 *
 * The sort ordering of a path is represented by a list of PathKey nodes.
 * An empty list implies no known ordering.  Otherwise the first item
 * represents the primary sort key, the second the first secondary sort key,
 * etc.  The value being sorted is represented by linking to an
 * EquivalenceClass containing that value and including pk_opfamily among its
 * ec_opfamilies.  The EquivalenceClass tells which collation to use, too.
 * This is a convenient method because it makes it trivial to detect
 * equivalent and closely-related orderings. (See optimizer/README for more
 * information.)
 *
 * Note: pk_strategy is either BTLessStrategyNumber (for ASC) or
 * BTGreaterStrategyNumber (for DESC).  We assume that all ordering-capable
 * index types will use btree-compatible strategy numbers.
 */
typedef struct PathKey
{
    NodeTag     type;

    EquivalenceClass *pk_eclass;    /* the value that is ordered */
    Oid         pk_opfamily;    /* btree opfamily defining the ordering */
    int         pk_strategy;    /* sort direction (ASC or DESC) */
    bool        pk_nulls_first; /* do NULLs come before normal values? */
} PathKey;


/*
 * ParamPathInfo
 *
 * All parameterized paths for a given relation with given required outer rels
 * link to a single ParamPathInfo, which stores common information such as
 * the estimated rowcount for this parameterization.  We do this partly to
 * avoid recalculations, but mostly to ensure that the estimated rowcount
 * is in fact the same for every such path.
 *
 * Note: ppi_clauses is only used in ParamPathInfos for base relation paths;
 * in join cases it's NIL because the set of relevant clauses varies depending
 * on how the join is formed.  The relevant clauses will appear in each
 * parameterized join path's joinrestrictinfo list, instead.
 */
typedef struct ParamPathInfo
{
    NodeTag     type;

    Relids      ppi_req_outer;  /* rels supplying parameters used by path */
    double      ppi_rows;       /* estimated number of result tuples */
    List       *ppi_clauses;    /* join clauses available from outer rels */
} ParamPathInfo;


/*
 * Type "Path" is used as-is for sequential-scan paths, as well as some other
 * simple plan types that we don't need any extra information in the path for.
 * For other path types it is the first component of a larger struct.
 *
 * "pathtype" is the NodeTag of the Plan node we could build from this Path.
 * It is partially redundant with the Path's NodeTag, but allows us to use
 * the same Path type for multiple Plan types when there is no need to
 * distinguish the Plan type during path processing.
 *
 * "param_info", if not NULL, links to a ParamPathInfo that identifies outer
 * relation(s) that provide parameter values to each scan of this path.
 * That means this path can only be joined to those rels by means of nestloop
 * joins with this path on the inside.  Also note that a parameterized path
 * is responsible for testing all "movable" joinclauses involving this rel
 * and the specified outer rel(s).
 *
 * "rows" is the same as parent->rows in simple paths, but in parameterized
 * paths and UniquePaths it can be less than parent->rows, reflecting the
 * fact that we've filtered by extra join conditions or removed duplicates.
 *
 * "pathkeys" is a List of PathKey nodes (see above), describing the sort
 * ordering of the path's output rows.
 */
typedef struct Path
{
    NodeTag     type;

    NodeTag     pathtype;       /* tag identifying scan/join method */

    RelOptInfo *parent;         /* the relation this path can build */
    ParamPathInfo *param_info;  /* parameterization info, or NULL if none */

    /* estimated size/costs for path (see costsize.c for more info) */
    double      rows;           /* estimated number of result tuples */
    Cost        startup_cost;   /* cost expended before fetching any tuples */
    Cost        total_cost;     /* total cost (assuming all tuples fetched) */

    List       *pathkeys;       /* sort ordering of path's output */
    /* pathkeys is a List of PathKey nodes; see above */
} Path;

/* Macro for extracting a path's parameterization relids; beware double eval */
#define PATH_REQ_OUTER(path)  \
    ((path)->param_info ? (path)->param_info->ppi_req_outer : (Relids) NULL)

/*----------
 * IndexPath represents an index scan over a single index.
 *
 * This struct is used for both regular indexscans and index-only scans;
 * path.pathtype is T_IndexScan or T_IndexOnlyScan to show which is meant.
 *
 * 'indexinfo' is the index to be scanned.
 *
 * 'indexclauses' is a list of index qualification clauses, with implicit
 * AND semantics across the list.  Each clause is a RestrictInfo node from
 * the query's WHERE or JOIN conditions.  An empty list implies a full
 * index scan.
 *
 * 'indexquals' has the same structure as 'indexclauses', but it contains
 * the actual index qual conditions that can be used with the index.
 * In simple cases this is identical to 'indexclauses', but when special
 * indexable operators appear in 'indexclauses', they are replaced by the
 * derived indexscannable conditions in 'indexquals'.
 *
 * 'indexqualcols' is an integer list of index column numbers (zero-based)
 * of the same length as 'indexquals', showing which index column each qual
 * is meant to be used with.  'indexquals' is required to be ordered by
 * index column, so 'indexqualcols' must form a nondecreasing sequence.
 * (The order of multiple quals for the same index column is unspecified.)
 *
 * 'indexorderbys', if not NIL, is a list of ORDER BY expressions that have
 * been found to be usable as ordering operators for an amcanorderbyop index.
 * The list must match the path's pathkeys, ie, one expression per pathkey
 * in the same order.  These are not RestrictInfos, just bare expressions,
 * since they generally won't yield booleans.  Also, unlike the case for
 * quals, it's guaranteed that each expression has the index key on the left
 * side of the operator.
 *
 * 'indexorderbycols' is an integer list of index column numbers (zero-based)
 * of the same length as 'indexorderbys', showing which index column each
 * ORDER BY expression is meant to be used with.  (There is no restriction
 * on which index column each ORDER BY can be used with.)
 *
 * 'indexscandir' is one of:
 *      ForwardScanDirection: forward scan of an ordered index
 *      BackwardScanDirection: backward scan of an ordered index
 *      NoMovementScanDirection: scan of an unordered index, or don't care
 * (The executor doesn't care whether it gets ForwardScanDirection or
 * NoMovementScanDirection for an indexscan, but the planner wants to
 * distinguish ordered from unordered indexes for building pathkeys.)
 *
 * 'indextotalcost' and 'indexselectivity' are saved in the IndexPath so that
 * we need not recompute them when considering using the same index in a
 * bitmap index/heap scan (see BitmapHeapPath).  The costs of the IndexPath
 * itself represent the costs of an IndexScan or IndexOnlyScan plan type.
 *----------
 */
typedef struct IndexPath
{
    Path        path;
    IndexOptInfo *indexinfo;
    List       *indexclauses;
    List       *indexquals;
    List       *indexqualcols;
    List       *indexorderbys;
    List       *indexorderbycols;
    ScanDirection indexscandir;
    Cost        indextotalcost;
    Selectivity indexselectivity;
} IndexPath;

/*
 * BitmapHeapPath represents one or more indexscans that generate TID bitmaps
 * instead of directly accessing the heap, followed by AND/OR combinations
 * to produce a single bitmap, followed by a heap scan that uses the bitmap.
 * Note that the output is always considered unordered, since it will come
 * out in physical heap order no matter what the underlying indexes did.
 *
 * The individual indexscans are represented by IndexPath nodes, and any
 * logic on top of them is represented by a tree of BitmapAndPath and
 * BitmapOrPath nodes.  Notice that we can use the same IndexPath node both
 * to represent a regular (or index-only) index scan plan, and as the child
 * of a BitmapHeapPath that represents scanning the same index using a
 * BitmapIndexScan.  The startup_cost and total_cost figures of an IndexPath
 * always represent the costs to use it as a regular (or index-only)
 * IndexScan.  The costs of a BitmapIndexScan can be computed using the
 * IndexPath's indextotalcost and indexselectivity.
 */
typedef struct BitmapHeapPath
{
    Path        path;
    Path       *bitmapqual;     /* IndexPath, BitmapAndPath, BitmapOrPath */
} BitmapHeapPath;

/*
 * BitmapAndPath represents a BitmapAnd plan node; it can only appear as
 * part of the substructure of a BitmapHeapPath.  The Path structure is
 * a bit more heavyweight than we really need for this, but for simplicity
 * we make it a derivative of Path anyway.
 */
typedef struct BitmapAndPath
{
    Path        path;
    List       *bitmapquals;    /* IndexPaths and BitmapOrPaths */
    Selectivity bitmapselectivity;
} BitmapAndPath;

/*
 * BitmapOrPath represents a BitmapOr plan node; it can only appear as
 * part of the substructure of a BitmapHeapPath.  The Path structure is
 * a bit more heavyweight than we really need for this, but for simplicity
 * we make it a derivative of Path anyway.
 */
typedef struct BitmapOrPath
{
    Path        path;
    List       *bitmapquals;    /* IndexPaths and BitmapAndPaths */
    Selectivity bitmapselectivity;
} BitmapOrPath;

/*
 * TidPath represents a scan by TID
 *
 * tidquals is an implicitly OR'ed list of qual expressions of the form
 * "CTID = pseudoconstant" or "CTID = ANY(pseudoconstant_array)".
 * Note they are bare expressions, not RestrictInfos.
 */
typedef struct TidPath
{
    Path        path;
    List       *tidquals;       /* qual(s) involving CTID = something */
} TidPath;

/*
 * ForeignPath represents a potential scan of a foreign table
 *
 * fdw_private stores FDW private data about the scan.  While fdw_private is
 * not actually touched by the core code during normal operations, it's
 * generally a good idea to use a representation that can be dumped by
 * nodeToString(), so that you can examine the structure during debugging
 * with tools like pprint().
 */
typedef struct ForeignPath
{
    Path        path;
    List       *fdw_private;
} ForeignPath;

/*
 * AppendPath represents an Append plan, ie, successive execution of
 * several member plans.
 *
 * Note: it is possible for "subpaths" to contain only one, or even no,
 * elements.  These cases are optimized during create_append_plan.
 * In particular, an AppendPath with no subpaths is a "dummy" path that
 * is created to represent the case that a relation is provably empty.
 */
typedef struct AppendPath
{
    Path        path;
    List       *subpaths;       /* list of component Paths */
} AppendPath;

#define IS_DUMMY_PATH(p) \
    (IsA((p), AppendPath) && ((AppendPath *) (p))->subpaths == NIL)

/* A relation that's been proven empty will have one path that is dummy */
#define IS_DUMMY_REL(r) \
    ((r)->cheapest_total_path != NULL && \
     IS_DUMMY_PATH((r)->cheapest_total_path))

/*
 * MergeAppendPath represents a MergeAppend plan, ie, the merging of sorted
 * results from several member plans to produce similarly-sorted output.
 */
typedef struct MergeAppendPath
{
    Path        path;
    List       *subpaths;       /* list of component Paths */
    double      limit_tuples;   /* hard limit on output tuples, or -1 */
} MergeAppendPath;

/*
 * ResultPath represents use of a Result plan node to compute a variable-free
 * targetlist with no underlying tables (a "SELECT expressions" query).
 * The query could have a WHERE clause, too, represented by "quals".
 *
 * Note that quals is a list of bare clauses, not RestrictInfos.
 */
typedef struct ResultPath
{
    Path        path;
    List       *quals;
} ResultPath;

/*
 * MaterialPath represents use of a Material plan node, i.e., caching of
 * the output of its subpath.  This is used when the subpath is expensive
 * and needs to be scanned repeatedly, or when we need mark/restore ability
 * and the subpath doesn't have it.
 */
typedef struct MaterialPath
{
    Path        path;
    Path       *subpath;
} MaterialPath;

/*
 * UniquePath represents elimination of distinct rows from the output of
 * its subpath.
 *
 * This is unlike the other Path nodes in that it can actually generate
 * different plans: either hash-based or sort-based implementation, or a
 * no-op if the input path can be proven distinct already.  The decision
 * is sufficiently localized that it's not worth having separate Path node
 * types.  (Note: in the no-op case, we could eliminate the UniquePath node
 * entirely and just return the subpath; but it's convenient to have a
 * UniquePath in the path tree to signal upper-level routines that the input
 * is known distinct.)
 */
typedef enum
{
    UNIQUE_PATH_NOOP,           /* input is known unique already */
    UNIQUE_PATH_HASH,           /* use hashing */
    UNIQUE_PATH_SORT            /* use sorting */
} UniquePathMethod;

typedef struct UniquePath
{
    Path        path;
    Path       *subpath;
    UniquePathMethod umethod;
    List       *in_operators;   /* equality operators of the IN clause */
    List       *uniq_exprs;     /* expressions to be made unique */
} UniquePath;

/*
 * All join-type paths share these fields.
 */

typedef struct JoinPath
{
    Path        path;

    JoinType    jointype;

    Path       *outerjoinpath;  /* path for the outer side of the join */
    Path       *innerjoinpath;  /* path for the inner side of the join */

    List       *joinrestrictinfo;       /* RestrictInfos to apply to join */

    /*
     * See the notes for RelOptInfo and ParamPathInfo to understand why
     * joinrestrictinfo is needed in JoinPath, and can't be merged into the
     * parent RelOptInfo.
     */
} JoinPath;

/*
 * A nested-loop path needs no special fields.
 */

typedef JoinPath NestPath;

/*
 * A mergejoin path has these fields.
 *
 * Unlike other path types, a MergePath node doesn't represent just a single
 * run-time plan node: it can represent up to four.  Aside from the MergeJoin
 * node itself, there can be a Sort node for the outer input, a Sort node
 * for the inner input, and/or a Material node for the inner input.  We could
 * represent these nodes by separate path nodes, but considering how many
 * different merge paths are investigated during a complex join problem,
 * it seems better to avoid unnecessary palloc overhead.
 *
 * path_mergeclauses lists the clauses (in the form of RestrictInfos)
 * that will be used in the merge.
 *
 * Note that the mergeclauses are a subset of the parent relation's
 * restriction-clause list.  Any join clauses that are not mergejoinable
 * appear only in the parent's restrict list, and must be checked by a
 * qpqual at execution time.
 *
 * outersortkeys (resp. innersortkeys) is NIL if the outer path
 * (resp. inner path) is already ordered appropriately for the
 * mergejoin.  If it is not NIL then it is a PathKeys list describing
 * the ordering that must be created by an explicit Sort node.
 *
 * materialize_inner is TRUE if a Material node should be placed atop the
 * inner input.  This may appear with or without an inner Sort step.
 */

typedef struct MergePath
{
    JoinPath    jpath;
    List       *path_mergeclauses;      /* join clauses to be used for merge */
    List       *outersortkeys;  /* keys for explicit sort, if any */
    List       *innersortkeys;  /* keys for explicit sort, if any */
    bool        materialize_inner;      /* add Materialize to inner? */
} MergePath;

/*
 * A hashjoin path has these fields.
 *
 * The remarks above for mergeclauses apply for hashclauses as well.
 *
 * Hashjoin does not care what order its inputs appear in, so we have
 * no need for sortkeys.
 */

typedef struct HashPath
{
    JoinPath    jpath;
    List       *path_hashclauses;       /* join clauses used for hashing */
    int         num_batches;    /* number of batches expected */
} HashPath;

/*
 * Restriction clause info.
 *
 * We create one of these for each AND sub-clause of a restriction condition
 * (WHERE or JOIN/ON clause).  Since the restriction clauses are logically
 * ANDed, we can use any one of them or any subset of them to filter out
 * tuples, without having to evaluate the rest.  The RestrictInfo node itself
 * stores data used by the optimizer while choosing the best query plan.
 *
 * If a restriction clause references a single base relation, it will appear
 * in the baserestrictinfo list of the RelOptInfo for that base rel.
 *
 * If a restriction clause references more than one base rel, it will
 * appear in the joininfo list of every RelOptInfo that describes a strict
 * subset of the base rels mentioned in the clause.  The joininfo lists are
 * used to drive join tree building by selecting plausible join candidates.
 * The clause cannot actually be applied until we have built a join rel
 * containing all the base rels it references, however.
 *
 * When we construct a join rel that includes all the base rels referenced
 * in a multi-relation restriction clause, we place that clause into the
 * joinrestrictinfo lists of paths for the join rel, if neither left nor
 * right sub-path includes all base rels referenced in the clause.  The clause
 * will be applied at that join level, and will not propagate any further up
 * the join tree.  (Note: the "predicate migration" code was once intended to
 * push restriction clauses up and down the plan tree based on evaluation
 * costs, but it's dead code and is unlikely to be resurrected in the
 * foreseeable future.)
 *
 * Note that in the presence of more than two rels, a multi-rel restriction
 * might reach different heights in the join tree depending on the join
 * sequence we use.  So, these clauses cannot be associated directly with
 * the join RelOptInfo, but must be kept track of on a per-join-path basis.
 *
 * RestrictInfos that represent equivalence conditions (i.e., mergejoinable
 * equalities that are not outerjoin-delayed) are handled a bit differently.
 * Initially we attach them to the EquivalenceClasses that are derived from
 * them.  When we construct a scan or join path, we look through all the
 * EquivalenceClasses and generate derived RestrictInfos representing the
 * minimal set of conditions that need to be checked for this particular scan
 * or join to enforce that all members of each EquivalenceClass are in fact
 * equal in all rows emitted by the scan or join.
 *
 * When dealing with outer joins we have to be very careful about pushing qual
 * clauses up and down the tree.  An outer join's own JOIN/ON conditions must
 * be evaluated exactly at that join node, unless they are "degenerate"
 * conditions that reference only Vars from the nullable side of the join.
 * Quals appearing in WHERE or in a JOIN above the outer join cannot be pushed
 * down below the outer join, if they reference any nullable Vars.
 * RestrictInfo nodes contain a flag to indicate whether a qual has been
 * pushed down to a lower level than its original syntactic placement in the
 * join tree would suggest.  If an outer join prevents us from pushing a qual
 * down to its "natural" semantic level (the level associated with just the
 * base rels used in the qual) then we mark the qual with a "required_relids"
 * value including more than just the base rels it actually uses.  By
 * pretending that the qual references all the rels required to form the outer
 * join, we prevent it from being evaluated below the outer join's joinrel.
 * When we do form the outer join's joinrel, we still need to distinguish
 * those quals that are actually in that join's JOIN/ON condition from those
 * that appeared elsewhere in the tree and were pushed down to the join rel
 * because they used no other rels.  That's what the is_pushed_down flag is
 * for; it tells us that a qual is not an OUTER JOIN qual for the set of base
 * rels listed in required_relids.  A clause that originally came from WHERE
 * or an INNER JOIN condition will *always* have its is_pushed_down flag set.
 * It's possible for an OUTER JOIN clause to be marked is_pushed_down too,
 * if we decide that it can be pushed down into the nullable side of the join.
 * In that case it acts as a plain filter qual for wherever it gets evaluated.
 * (In short, is_pushed_down is only false for non-degenerate outer join
 * conditions.  Possibly we should rename it to reflect that meaning?)
 *
 * RestrictInfo nodes also contain an outerjoin_delayed flag, which is true
 * if the clause's applicability must be delayed due to any outer joins
 * appearing below it (ie, it has to be postponed to some join level higher
 * than the set of relations it actually references).
 *
 * There is also an outer_relids field, which is NULL except for outer join
 * clauses; for those, it is the set of relids on the outer side of the
 * clause's outer join.  (These are rels that the clause cannot be applied to
 * in parameterized scans, since pushing it into the join's outer side would
 * lead to wrong answers.)
 *
 * There is also a nullable_relids field, which is the set of rels the clause
 * references that can be forced null by some outer join below the clause.
 *
 * outerjoin_delayed = true is subtly different from nullable_relids != NULL:
 * a clause might reference some nullable rels and yet not be
 * outerjoin_delayed because it also references all the other rels of the
 * outer join(s). A clause that is not outerjoin_delayed can be enforced
 * anywhere it is computable.
 *
 * In general, the referenced clause might be arbitrarily complex.  The
 * kinds of clauses we can handle as indexscan quals, mergejoin clauses,
 * or hashjoin clauses are limited (e.g., no volatile functions).  The code
 * for each kind of path is responsible for identifying the restrict clauses
 * it can use and ignoring the rest.  Clauses not implemented by an indexscan,
 * mergejoin, or hashjoin will be placed in the plan qual or joinqual field
 * of the finished Plan node, where they will be enforced by general-purpose
 * qual-expression-evaluation code.  (But we are still entitled to count
 * their selectivity when estimating the result tuple count, if we
 * can guess what it is...)
 *
 * When the referenced clause is an OR clause, we generate a modified copy
 * in which additional RestrictInfo nodes are inserted below the top-level
 * OR/AND structure.  This is a convenience for OR indexscan processing:
 * indexquals taken from either the top level or an OR subclause will have
 * associated RestrictInfo nodes.
 *
 * The can_join flag is set true if the clause looks potentially useful as
 * a merge or hash join clause, that is if it is a binary opclause with
 * nonoverlapping sets of relids referenced in the left and right sides.
 * (Whether the operator is actually merge or hash joinable isn't checked,
 * however.)
 *
 * The pseudoconstant flag is set true if the clause contains no Vars of
 * the current query level and no volatile functions.  Such a clause can be
 * pulled out and used as a one-time qual in a gating Result node.  We keep
 * pseudoconstant clauses in the same lists as other RestrictInfos so that
 * the regular clause-pushing machinery can assign them to the correct join
 * level, but they need to be treated specially for cost and selectivity
 * estimates.  Note that a pseudoconstant clause can never be an indexqual
 * or merge or hash join clause, so it's of no interest to large parts of
 * the planner.
 *
 * When join clauses are generated from EquivalenceClasses, there may be
 * several equally valid ways to enforce join equivalence, of which we need
 * apply only one.  We mark clauses of this kind by setting parent_ec to
 * point to the generating EquivalenceClass.  Multiple clauses with the same
 * parent_ec in the same join are redundant.
 */

typedef struct RestrictInfo
{
    NodeTag     type;

    Expr       *clause;         /* the represented clause of WHERE or JOIN */

    bool        is_pushed_down; /* TRUE if clause was pushed down in level */

    bool        outerjoin_delayed;      /* TRUE if delayed by lower outer join */

    bool        can_join;       /* see comment above */

    bool        pseudoconstant; /* see comment above */

    /* The set of relids (varnos) actually referenced in the clause: */
    Relids      clause_relids;

    /* The set of relids required to evaluate the clause: */
    Relids      required_relids;

    /* If an outer-join clause, the outer-side relations, else NULL: */
    Relids      outer_relids;

    /* The relids used in the clause that are nullable by lower outer joins: */
    Relids      nullable_relids;

    /* These fields are set for any binary opclause: */
    Relids      left_relids;    /* relids in left side of clause */
    Relids      right_relids;   /* relids in right side of clause */

    /* This field is NULL unless clause is an OR clause: */
    Expr       *orclause;       /* modified clause with RestrictInfos */

    /* This field is NULL unless clause is potentially redundant: */
    EquivalenceClass *parent_ec;    /* generating EquivalenceClass */

    /* cache space for cost and selectivity */
    QualCost    eval_cost;      /* eval cost of clause; -1 if not yet set */
    Selectivity norm_selec;     /* selectivity for "normal" (JOIN_INNER)
                                 * semantics; -1 if not yet set; >1 means a
                                 * redundant clause */
    Selectivity outer_selec;    /* selectivity for outer join semantics; -1 if
                                 * not yet set */

    /* valid if clause is mergejoinable, else NIL */
    List       *mergeopfamilies;    /* opfamilies containing clause operator */

    /* cache space for mergeclause processing; NULL if not yet set */
    EquivalenceClass *left_ec;  /* EquivalenceClass containing lefthand */
    EquivalenceClass *right_ec; /* EquivalenceClass containing righthand */
    EquivalenceMember *left_em; /* EquivalenceMember for lefthand */
    EquivalenceMember *right_em;    /* EquivalenceMember for righthand */
    List       *scansel_cache;  /* list of MergeScanSelCache structs */

    /* transient workspace for use while considering a specific join path */
    bool        outer_is_left;  /* T = outer var on left, F = on right */

    /* valid if clause is hashjoinable, else InvalidOid: */
    Oid         hashjoinoperator;       /* copy of clause operator */

    /* cache space for hashclause processing; -1 if not yet set */
    Selectivity left_bucketsize;    /* avg bucketsize of left side */
    Selectivity right_bucketsize;       /* avg bucketsize of right side */
} RestrictInfo;

/*
 * Since mergejoinscansel() is a relatively expensive function, and would
 * otherwise be invoked many times while planning a large join tree,
 * we go out of our way to cache its results.  Each mergejoinable
 * RestrictInfo carries a list of the specific sort orderings that have
 * been considered for use with it, and the resulting selectivities.
 */
typedef struct MergeScanSelCache
{
    /* Ordering details (cache lookup key) */
    Oid         opfamily;       /* btree opfamily defining the ordering */
    Oid         collation;      /* collation for the ordering */
    int         strategy;       /* sort direction (ASC or DESC) */
    bool        nulls_first;    /* do NULLs come before normal values? */
    /* Results */
    Selectivity leftstartsel;   /* first-join fraction for clause left side */
    Selectivity leftendsel;     /* last-join fraction for clause left side */
    Selectivity rightstartsel;  /* first-join fraction for clause right side */
    Selectivity rightendsel;    /* last-join fraction for clause right side */
} MergeScanSelCache;

/*
 * Placeholder node for an expression to be evaluated below the top level
 * of a plan tree.  This is used during planning to represent the contained
 * expression.  At the end of the planning process it is replaced by either
 * the contained expression or a Var referring to a lower-level evaluation of
 * the contained expression.  Typically the evaluation occurs below an outer
 * join, and Var references above the outer join might thereby yield NULL
 * instead of the expression value.
 *
 * Although the planner treats this as an expression node type, it is not
 * recognized by the parser or executor, so we declare it here rather than
 * in primnodes.h.
 */

typedef struct PlaceHolderVar
{
    Expr        xpr;
    Expr       *phexpr;         /* the represented expression */
    Relids      phrels;         /* base relids syntactically within expr src */
    Index       phid;           /* ID for PHV (unique within planner run) */
    Index       phlevelsup;     /* > 0 if PHV belongs to outer query */
} PlaceHolderVar;

/*
 * "Special join" info.
 *
 * One-sided outer joins constrain the order of joining partially but not
 * completely.  We flatten such joins into the planner's top-level list of
 * relations to join, but record information about each outer join in a
 * SpecialJoinInfo struct.  These structs are kept in the PlannerInfo node's
 * join_info_list.
 *
 * Similarly, semijoins and antijoins created by flattening IN (subselect)
 * and EXISTS(subselect) clauses create partial constraints on join order.
 * These are likewise recorded in SpecialJoinInfo structs.
 *
 * We make SpecialJoinInfos for FULL JOINs even though there is no flexibility
 * of planning for them, because this simplifies make_join_rel()'s API.
 *
 * min_lefthand and min_righthand are the sets of base relids that must be
 * available on each side when performing the special join.  lhs_strict is
 * true if the special join's condition cannot succeed when the LHS variables
 * are all NULL (this means that an outer join can commute with upper-level
 * outer joins even if it appears in their RHS).  We don't bother to set
 * lhs_strict for FULL JOINs, however.
 *
 * It is not valid for either min_lefthand or min_righthand to be empty sets;
 * if they were, this would break the logic that enforces join order.
 *
 * syn_lefthand and syn_righthand are the sets of base relids that are
 * syntactically below this special join.  (These are needed to help compute
 * min_lefthand and min_righthand for higher joins.)
 *
 * delay_upper_joins is set TRUE if we detect a pushed-down clause that has
 * to be evaluated after this join is formed (because it references the RHS).
 * Any outer joins that have such a clause and this join in their RHS cannot
 * commute with this join, because that would leave noplace to check the
 * pushed-down clause.  (We don't track this for FULL JOINs, either.)
 *
 * join_quals is an implicit-AND list of the quals syntactically associated
 * with the join (they may or may not end up being applied at the join level).
 * This is just a side list and does not drive actual application of quals.
 * For JOIN_SEMI joins, this is cleared to NIL in create_unique_path() if
 * the join is found not to be suitable for a uniqueify-the-RHS plan.
 *
 * jointype is never JOIN_RIGHT; a RIGHT JOIN is handled by switching
 * the inputs to make it a LEFT JOIN.  So the allowed values of jointype
 * in a join_info_list member are only LEFT, FULL, SEMI, or ANTI.
 *
 * For purposes of join selectivity estimation, we create transient
 * SpecialJoinInfo structures for regular inner joins; so it is possible
 * to have jointype == JOIN_INNER in such a structure, even though this is
 * not allowed within join_info_list.  We also create transient
 * SpecialJoinInfos with jointype == JOIN_INNER for outer joins, since for
 * cost estimation purposes it is sometimes useful to know the join size under
 * plain innerjoin semantics.  Note that lhs_strict, delay_upper_joins, and
 * join_quals are not set meaningfully within such structs.
 */

typedef struct SpecialJoinInfo
{
    NodeTag     type;
    Relids      min_lefthand;   /* base relids in minimum LHS for join */
    Relids      min_righthand;  /* base relids in minimum RHS for join */
    Relids      syn_lefthand;   /* base relids syntactically within LHS */
    Relids      syn_righthand;  /* base relids syntactically within RHS */
    JoinType    jointype;       /* always INNER, LEFT, FULL, SEMI, or ANTI */
    bool        lhs_strict;     /* joinclause is strict for some LHS rel */
    bool        delay_upper_joins;      /* can't commute with upper RHS */
    List       *join_quals;     /* join quals, in implicit-AND list format */
} SpecialJoinInfo;

/*
 * "Lateral join" info.
 *
 * Lateral references in subqueries constrain the join order in a way that's
 * somewhat like outer joins, though different in detail.  We construct one or
 * more LateralJoinInfos for each RTE with lateral references, and add them to
 * the PlannerInfo node's lateral_info_list.
 *
 * lateral_rhs is the relid of a baserel with lateral references, and
 * lateral_lhs is a set of relids of baserels it references, all of which
 * must be present on the LHS to compute a parameter needed by the RHS.
 * Typically, lateral_lhs is a singleton, but it can include multiple rels
 * if the RHS references a PlaceHolderVar with a multi-rel ph_eval_at level.
 * We disallow joining to only part of the LHS in such cases, since that would
 * result in a join tree with no convenient place to compute the PHV.
 *
 * When an appendrel contains lateral references (eg "LATERAL (SELECT x.col1
 * UNION ALL SELECT y.col2)"), the LateralJoinInfos reference the parent
 * baserel not the member otherrels, since it is the parent relid that is
 * considered for joining purposes.
 */

typedef struct LateralJoinInfo
{
    NodeTag     type;
    Index       lateral_rhs;    /* a baserel containing lateral refs */
    Relids      lateral_lhs;    /* some base relids it references */
} LateralJoinInfo;

/*
 * Append-relation info.
 *
 * When we expand an inheritable table or a UNION-ALL subselect into an
 * "append relation" (essentially, a list of child RTEs), we build an
 * AppendRelInfo for each child RTE.  The list of AppendRelInfos indicates
 * which child RTEs must be included when expanding the parent, and each
 * node carries information needed to translate Vars referencing the parent
 * into Vars referencing that child.
 *
 * These structs are kept in the PlannerInfo node's append_rel_list.
 * Note that we just throw all the structs into one list, and scan the
 * whole list when desiring to expand any one parent.  We could have used
 * a more complex data structure (eg, one list per parent), but this would
 * be harder to update during operations such as pulling up subqueries,
 * and not really any easier to scan.  Considering that typical queries
 * will not have many different append parents, it doesn't seem worthwhile
 * to complicate things.
 *
 * Note: after completion of the planner prep phase, any given RTE is an
 * append parent having entries in append_rel_list if and only if its
 * "inh" flag is set.  We clear "inh" for plain tables that turn out not
 * to have inheritance children, and (in an abuse of the original meaning
 * of the flag) we set "inh" for subquery RTEs that turn out to be
 * flattenable UNION ALL queries.  This lets us avoid useless searches
 * of append_rel_list.
 *
 * Note: the data structure assumes that append-rel members are single
 * baserels.  This is OK for inheritance, but it prevents us from pulling
 * up a UNION ALL member subquery if it contains a join.  While that could
 * be fixed with a more complex data structure, at present there's not much
 * point because no improvement in the plan could result.
 */

typedef struct AppendRelInfo
{
    NodeTag     type;

    /*
     * These fields uniquely identify this append relationship.  There can be
     * (in fact, always should be) multiple AppendRelInfos for the same
     * parent_relid, but never more than one per child_relid, since a given
     * RTE cannot be a child of more than one append parent.
     */
    Index       parent_relid;   /* RT index of append parent rel */
    Index       child_relid;    /* RT index of append child rel */

    /*
     * For an inheritance appendrel, the parent and child are both regular
     * relations, and we store their rowtype OIDs here for use in translating
     * whole-row Vars.  For a UNION-ALL appendrel, the parent and child are
     * both subqueries with no named rowtype, and we store InvalidOid here.
     */
    Oid         parent_reltype; /* OID of parent's composite type */
    Oid         child_reltype;  /* OID of child's composite type */

    /*
     * The N'th element of this list is a Var or expression representing the
     * child column corresponding to the N'th column of the parent. This is
     * used to translate Vars referencing the parent rel into references to
     * the child.  A list element is NULL if it corresponds to a dropped
     * column of the parent (this is only possible for inheritance cases, not
     * UNION ALL).  The list elements are always simple Vars for inheritance
     * cases, but can be arbitrary expressions in UNION ALL cases.
     *
     * Notice we only store entries for user columns (attno > 0).  Whole-row
     * Vars are special-cased, and system columns (attno < 0) need no special
     * translation since their attnos are the same for all tables.
     *
     * Caution: the Vars have varlevelsup = 0.  Be careful to adjust as needed
     * when copying into a subquery.
     */
    List       *translated_vars;    /* Expressions in the child's Vars */

    /*
     * We store the parent table's OID here for inheritance, or InvalidOid for
     * UNION ALL.  This is only needed to help in generating error messages if
     * an attempt is made to reference a dropped parent column.
     */
    Oid         parent_reloid;  /* OID of parent relation */
} AppendRelInfo;

/*
 * For each distinct placeholder expression generated during planning, we
 * store a PlaceHolderInfo node in the PlannerInfo node's placeholder_list.
 * This stores info that is needed centrally rather than in each copy of the
 * PlaceHolderVar.  The phid fields identify which PlaceHolderInfo goes with
 * each PlaceHolderVar.  Note that phid is unique throughout a planner run,
 * not just within a query level --- this is so that we need not reassign ID's
 * when pulling a subquery into its parent.
 *
 * The idea is to evaluate the expression at (only) the ph_eval_at join level,
 * then allow it to bubble up like a Var until the ph_needed join level.
 * ph_needed has the same definition as attr_needed for a regular Var.
 *
 * ph_may_need is an initial estimate of ph_needed, formed using the
 * syntactic locations of references to the PHV.  We need this in order to
 * determine whether the PHV reference forces a join ordering constraint:
 * if the PHV has to be evaluated below the nullable side of an outer join,
 * and then used above that outer join, we must constrain join order to ensure
 * there's a valid place to evaluate the PHV below the join.  The final
 * actual ph_needed level might be lower than ph_may_need, but we can't
 * determine that until later on.  Fortunately this doesn't matter for what
 * we need ph_may_need for: if there's a PHV reference syntactically
 * above the outer join, it's not going to be allowed to drop below the outer
 * join, so we would come to the same conclusions about join order even if
 * we had the final ph_needed value to compare to.
 *
 * We create a PlaceHolderInfo only after determining that the PlaceHolderVar
 * is actually referenced in the plan tree, so that unreferenced placeholders
 * don't result in unnecessary constraints on join order.
 */

typedef struct PlaceHolderInfo
{
    NodeTag     type;

    Index       phid;           /* ID for PH (unique within planner run) */
    PlaceHolderVar *ph_var;     /* copy of PlaceHolderVar tree */
    Relids      ph_eval_at;     /* lowest level we can evaluate value at */
    Relids      ph_needed;      /* highest level the value is needed at */
    Relids      ph_may_need;    /* highest level it might be needed at */
    int32       ph_width;       /* estimated attribute width */
} PlaceHolderInfo;

/*
 * For each potentially index-optimizable MIN/MAX aggregate function,
 * root->minmax_aggs stores a MinMaxAggInfo describing it.
 */
typedef struct MinMaxAggInfo
{
    NodeTag     type;

    Oid         aggfnoid;       /* pg_proc Oid of the aggregate */
    Oid         aggsortop;      /* Oid of its sort operator */
    Expr       *target;         /* expression we are aggregating on */
    PlannerInfo *subroot;       /* modified "root" for planning the subquery */
    Path       *path;           /* access path for subquery */
    Cost        pathcost;       /* estimated cost to fetch first row */
    Param      *param;          /* param for subplan's output */
} MinMaxAggInfo;

/*
 * At runtime, PARAM_EXEC slots are used to pass values around from one plan
 * node to another.  They can be used to pass values down into subqueries (for
 * outer references in subqueries), or up out of subqueries (for the results
 * of a subplan), or from a NestLoop plan node into its inner relation (when
 * the inner scan is parameterized with values from the outer relation).
 * The planner is responsible for assigning nonconflicting PARAM_EXEC IDs to
 * the PARAM_EXEC Params it generates.
 *
 * Outer references are managed via root->plan_params, which is a list of
 * PlannerParamItems.  While planning a subquery, each parent query level's
 * plan_params contains the values required from it by the current subquery.
 * During create_plan(), we use plan_params to track values that must be
 * passed from outer to inner sides of NestLoop plan nodes.
 *
 * The item a PlannerParamItem represents can be one of three kinds:
 *
 * A Var: the slot represents a variable of this level that must be passed
 * down because subqueries have outer references to it, or must be passed
 * from a NestLoop node to its inner scan.  The varlevelsup value in the Var
 * will always be zero.
 *
 * A PlaceHolderVar: this works much like the Var case, except that the
 * entry is a PlaceHolderVar node with a contained expression.  The PHV
 * will have phlevelsup = 0, and the contained expression is adjusted
 * to match in level.
 *
 * An Aggref (with an expression tree representing its argument): the slot
 * represents an aggregate expression that is an outer reference for some
 * subquery.  The Aggref itself has agglevelsup = 0, and its argument tree
 * is adjusted to match in level.
 *
 * Note: we detect duplicate Var and PlaceHolderVar parameters and coalesce
 * them into one slot, but we do not bother to do that for Aggrefs.
 * The scope of duplicate-elimination only extends across the set of
 * parameters passed from one query level into a single subquery, or for
 * nestloop parameters across the set of nestloop parameters used in a single
 * query level.  So there is no possibility of a PARAM_EXEC slot being used
 * for conflicting purposes.
 *
 * In addition, PARAM_EXEC slots are assigned for Params representing outputs
 * from subplans (values that are setParam items for those subplans).  These
 * IDs need not be tracked via PlannerParamItems, since we do not need any
 * duplicate-elimination nor later processing of the represented expressions.
 * Instead, we just record the assignment of the slot number by incrementing
 * root->glob->nParamExec.
 */
typedef struct PlannerParamItem
{
    NodeTag     type;

    Node       *item;           /* the Var, PlaceHolderVar, or Aggref */
    int         paramId;        /* its assigned PARAM_EXEC slot number */
} PlannerParamItem;

/*
 * When making cost estimates for a SEMI or ANTI join, there are some
 * correction factors that are needed in both nestloop and hash joins
 * to account for the fact that the executor can stop scanning inner rows
 * as soon as it finds a match to the current outer row.  These numbers
 * depend only on the selected outer and inner join relations, not on the
 * particular paths used for them, so it's worthwhile to calculate them
 * just once per relation pair not once per considered path.  This struct
 * is filled by compute_semi_anti_join_factors and must be passed along
 * to the join cost estimation functions.
 *
 * outer_match_frac is the fraction of the outer tuples that are
 *      expected to have at least one match.
 * match_count is the average number of matches expected for
 *      outer tuples that have at least one match.
 */
typedef struct SemiAntiJoinFactors
{
    Selectivity outer_match_frac;
    Selectivity match_count;
} SemiAntiJoinFactors;

/*
 * For speed reasons, cost estimation for join paths is performed in two
 * phases: the first phase tries to quickly derive a lower bound for the
 * join cost, and then we check if that's sufficient to reject the path.
 * If not, we come back for a more refined cost estimate.  The first phase
 * fills a JoinCostWorkspace struct with its preliminary cost estimates
 * and possibly additional intermediate values.  The second phase takes
 * these values as inputs to avoid repeating work.
 *
 * (Ideally we'd declare this in cost.h, but it's also needed in pathnode.h,
 * so seems best to put it here.)
 */
typedef struct JoinCostWorkspace
{
    /* Preliminary cost estimates --- must not be larger than final ones! */
    Cost        startup_cost;   /* cost expended before fetching any tuples */
    Cost        total_cost;     /* total cost (assuming all tuples fetched) */

    /* Fields below here should be treated as private to costsize.c */
    Cost        run_cost;       /* non-startup cost components */

    /* private for cost_nestloop code */
    Cost        inner_rescan_run_cost;
    double      outer_matched_rows;
    Selectivity inner_scan_frac;

    /* private for cost_mergejoin code */
    Cost        inner_run_cost;
    double      outer_rows;
    double      inner_rows;
    double      outer_skip_rows;
    double      inner_skip_rows;

    /* private for cost_hashjoin code */
    int         numbuckets;
    int         numbatches;
} JoinCostWorkspace;

#endif   /* RELATION_H */