Trivial fix: change the reference to further documentation of pathkeys to

[postgresql] / src / include / nodes / relation.h

/*-------------------------------------------------------------------------
 *
 * relation.h
 *        Definitions for planner's internal data structures.
 *
 *
 * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * $PostgreSQL: pgsql/src/include/nodes/relation.h,v 1.103 2005/02/21 06:43:04 neilc Exp $
 *
 *-------------------------------------------------------------------------
 */
#ifndef RELATION_H
#define RELATION_H

#include "access/sdir.h"
#include "nodes/bitmapset.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;

/*----------
 * 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 Query's
 * base_rel_list 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 stored
 * in other_rel_list not base_rel_list.
 *
 * Currently the only kind of otherrels are those made for child relations
 * of an inheritance scan (SELECT FROM foo*).  The parent table's RTE and
 * corresponding baserel represent the whole result of the inheritance scan.
 * The planner creates separate RTEs and associated RelOptInfos for each child
 * table (including the parent table, in its capacity as a member of the
 * inheritance set).  These RelOptInfos are physically identical to baserels,
 * but are otherrels because they are not in the main join tree.  These added
 * RTEs and otherrels are used to plan the scans of the individual tables in
 * the inheritance set; then the parent baserel is given an Append plan
 * comprising the best plans for the individual child tables.
 *
 * 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)
 *              reltargetlist - List of Var nodes for the attributes we need to
 *                                              output from this relation (in no particular order)
 *                                              NOTE: in a child relation, may contain RowExprs
 *              pathlist - List of Path nodes, one for each potentially useful
 *                                 method of generating the relation
 *              cheapest_startup_path - the pathlist member with lowest startup cost
 *                                                              (regardless of its ordering)
 *              cheapest_total_path - the pathlist member with lowest total cost
 *                                                        (regardless of its ordering)
 *              cheapest_unique_path - for caching cheapest path to produce unique
 *                                                         (no duplicates) output from relation
 *
 * 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
 *              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)
 *              subplan - plan for subquery (NULL if it's not a subquery)
 *
 *              Note: for a subquery, tuples and subplan are not set immediately
 *              upon creation of the RelOptInfo object; they are filled in when
 *              set_base_rel_pathlist processes the object.
 *
 *              For otherrels that are inheritance children, 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 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)
 *              outerjoinset - For a base rel: if the rel appears within the nullable
 *                                      side of an outer join, the set of all relids
 *                                      participating in the highest such outer join; else NULL.
 *                                      Otherwise, unused.
 *              joininfo  - List of JoinInfo nodes, containing info about each join
 *                                      clause in which this relation participates
 *              index_outer_relids - only used for base rels; set of outer relids
 *                                      that participate in indexable joinclauses for this rel
 *              index_inner_paths - only used for base rels; list of InnerIndexscanInfo
 *                                      nodes showing best indexpaths for various subsets of
 *                                      index_outer_relids.
 *
 * 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 lists, because those are 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.
 *
 * outerjoinset is used to ensure correct placement of WHERE clauses that
 * apply to outer-joined relations; we must not apply such WHERE clauses
 * until after the outer join is performed.
 *----------
 */
typedef enum RelOptKind
{
        RELOPT_BASEREL,
        RELOPT_JOINREL,
        RELOPT_OTHER_CHILD_REL
} 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 */

        /* materialization information */
        List       *reltargetlist;      /* needed Vars */
        List       *pathlist;           /* Path structures */
        struct Path *cheapest_startup_path;
        struct Path *cheapest_total_path;
        struct Path *cheapest_unique_path;

        /* information about a base rel (not set for join rels!) */
        Index           relid;
        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       *indexlist;
        BlockNumber     pages;
        double          tuples;
        struct Plan *subplan;           /* if subquery */

        /* used by various scans and joins: */
        List       *baserestrictinfo;           /* RestrictInfo structures (if
                                                                                 * base rel) */
        QualCost        baserestrictcost;               /* cost of evaluating the above */
        Relids          outerjoinset;   /* set of base relids */
        List       *joininfo;           /* JoinInfo structures */

        /* cached info about inner indexscan paths for relation: */
        Relids          index_outer_relids;             /* other relids in indexable join
                                                                                 * clauses */
        List       *index_inner_paths;          /* InnerIndexscanInfo nodes */

        /*
         * Inner indexscans are not in the main pathlist because they are not
         * usable except in specific join contexts.  We use the
         * index_inner_paths list just to avoid recomputing the best inner
         * indexscan repeatedly for similar outer relations.  See comments for
         * InnerIndexscanInfo.
         */
} RelOptInfo;

/*
 * IndexOptInfo
 *              Per-index information for planning/optimization
 *
 *              Prior to Postgres 7.0, RelOptInfo was used to describe both relations
 *              and indexes, but that created confusion without actually doing anything
 *              useful.  So now we have a separate IndexOptInfo struct for indexes.
 *
 *              classlist[], indexkeys[], and ordering[] have ncolumns entries.
 *              Zeroes in the indexkeys[] array indicate index columns that are
 *              expressions; there is one element in indexprs for each such column.
 *
 *              Note: for historical reasons, the classlist and ordering arrays have
 *              an extra entry that is always zero.  Some code scans until it sees a
 *              zero entry, rather than looking at ncolumns.
 *
 *              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.
 */

typedef struct IndexOptInfo
{
        NodeTag         type;

        Oid                     indexoid;               /* OID of the index relation */

        /* statistics from pg_class */
        BlockNumber     pages;                  /* number of disk pages in index */
        double          tuples;                 /* number of index tuples in index */

        /* index descriptor information */
        int                     ncolumns;               /* number of columns in index */
        Oid                *classlist;          /* OIDs of operator classes for columns */
        int                *indexkeys;          /* column numbers of index's keys, or 0 */
        Oid                *ordering;           /* OIDs of sort operators for each column */
        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 */

        bool            predOK;                 /* true if predicate matches query */
        bool            unique;                 /* true if a unique index */

        /* cached info about inner indexscan paths for index */
        Relids          outer_relids;   /* other relids in usable join clauses */
        List       *inner_paths;        /* List of InnerIndexscanInfo nodes */
} IndexOptInfo;


/*
 * PathKeys
 *
 *      The sort ordering of a path is represented by a list of sublists of
 *      PathKeyItem nodes.      An empty list implies no known ordering.  Otherwise
 *      the first sublist represents the primary sort key, the second the
 *      first secondary sort key, etc.  Each sublist contains one or more
 *      PathKeyItem nodes, each of which can be taken as the attribute that
 *      appears at that sort position.  (See optimizer/README for more
 *      information.)
 */

typedef struct PathKeyItem
{
        NodeTag         type;

        Node       *key;                        /* the item that is ordered */
        Oid                     sortop;                 /* the ordering operator ('<' op) */

        /*
         * key typically points to a Var node, ie a relation attribute, but it
         * can also point to an arbitrary expression representing the value
         * indexed by an index expression.
         */
} PathKeyItem;

/*
 * Type "Path" is used as-is for sequential-scan paths.  For other
 * path types it is the first component of a larger struct.
 *
 * Note: "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 where there is no need
 * to distinguish the Plan type during path processing.
 */

typedef struct Path
{
        NodeTag         type;

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

        RelOptInfo *parent;                     /* the relation this path can build */

        /* estimated execution costs for path (see costsize.c for more info) */
        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 Lists of PathKeyItem nodes; see above */
} Path;

/*----------
 * IndexPath represents an index scan.  Although an indexscan can only read
 * a single relation, it can scan it more than once, potentially using a
 * different index during each scan.  The result is the union (OR) of all the
 * tuples matched during any scan.      (The executor is smart enough not to return
 * the same tuple more than once, even if it is matched in multiple scans.)
 *
 * 'indexinfo' is a list of IndexOptInfo nodes, one per scan to be performed.
 *
 * 'indexclauses' is a list of index qualifications, also one per scan.
 * Each entry in 'indexclauses' is a sublist of qualification clauses to be
 * used for that scan, with implicit AND semantics across the sublist items.
 * NOTE that the semantics of the top-level list in 'indexclauses' is OR
 * combination, while the sublists are implicitly AND combinations!
 *
 * 'indexquals' has the same structure as 'indexclauses', but it contains
 * the actual indexqual conditions that can be used with the index(es).
 * 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'.
 *
 * Both 'indexclauses' and 'indexquals' are lists of sublists of RestrictInfo
 * nodes.  (Before 8.0, we kept bare operator expressions in these lists, but
 * storing RestrictInfos is more efficient since selectivities can be cached.)
 *
 * 'isjoininner' is TRUE if the path is a nestloop inner scan (that is,
 * some of the index conditions are join rather than restriction clauses).
 *
 * '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.)
 *
 * 'rows' is the estimated result tuple count for the indexscan.  This
 * is the same as path.parent->rows for a simple indexscan, but it is
 * different for a nestloop inner scan, because the additional indexquals
 * coming from join clauses make the scan more selective than the parent
 * rel's restrict clauses alone would do.
 *----------
 */
typedef struct IndexPath
{
        Path            path;
        List       *indexinfo;
        List       *indexclauses;
        List       *indexquals;
        bool            isjoininner;
        ScanDirection indexscandir;
        double          rows;                   /* estimated number of result tuples */
} IndexPath;

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

/*
 * AppendPath represents an Append plan, ie, successive execution of
 * several member plans.  Currently it is only used to handle expansion
 * of inheritance trees.
 */
typedef struct AppendPath
{
        Path            path;
        List       *subpaths;           /* list of component Paths */
} AppendPath;

/*
 * ResultPath represents use of a Result plan node, either to compute a
 * variable-free targetlist or to gate execution of a subplan with a
 * one-time (variable-free) qual condition.  Note that in the former case
 * path.parent will be NULL; in the latter case it is copied from the subpath.
 *
 * Note that constantqual is a list of bare clauses, not RestrictInfos.
 */
typedef struct ResultPath
{
        Path            path;
        Path       *subpath;
        List       *constantqual;
} 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;
        double          rows;                   /* estimated number of result tuples */
} 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 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.
 *
 * 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 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 */
} 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 */
} 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 lists 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.
 *
 * 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, and any quals appearing in WHERE or
 * in a JOIN above the outer join cannot be pushed down below the outer join.
 * Otherwise the outer join will produce wrong results because it will see the
 * wrong sets of input rows.  All quals are stored as RestrictInfo nodes
 * during planning, but there's 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 the qual will appear in JoinInfo lists
 * that reference more than just the base rels it actually uses.  By
 * pretending that the qual references all the rels appearing in 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 higher 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 came from a point above the join of the
 * specific set of base rels that it uses (or that the JoinInfo structures
 * claim it uses).      A clause that originally came from WHERE will *always*
 * have its is_pushed_down flag set; a clause that came from an INNER JOIN
 * condition, but doesn't use all the rels being joined, will also have
 * is_pushed_down set because it will get attached to some lower joinrel.
 *
 * We also store a valid_everywhere flag, which says that the clause is not
 * affected by any lower-level outer join, and therefore any conditions it
 * asserts can be presumed true throughout the plan tree.
 *
 * 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 fairly limited --- 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.
 */

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            valid_everywhere;               /* TRUE if valid on every level */

        /*
         * This 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.)
         */
        bool            can_join;

        /* The set of relids (varnos) referenced in the clause: */
        Relids          clause_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 */

        /* cache space for cost and selectivity */
        QualCost        eval_cost;              /* eval cost of clause; -1 if not yet set */
        Selectivity this_selec;         /* selectivity; -1 if not yet set */

        /* valid if clause is mergejoinable, else InvalidOid: */
        Oid                     mergejoinoperator;              /* copy of clause operator */
        Oid                     left_sortop;    /* leftside sortop needed for mergejoin */
        Oid                     right_sortop;   /* rightside sortop needed for mergejoin */

        /* cache space for mergeclause processing; NIL if not yet set */
        List       *left_pathkey;       /* canonical pathkey for left side */
        List       *right_pathkey;      /* canonical pathkey for right side */

        /* cache space for mergeclause processing; -1 if not yet set */
        Selectivity left_mergescansel;          /* fraction of left side to scan */
        Selectivity right_mergescansel;         /* fraction of right side to scan */

        /* 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;

/*
 * Join clause info.
 *
 * We make a list of these for each RelOptInfo, containing info about
 * all the join clauses this RelOptInfo participates in.  (For this
 * purpose, a "join clause" is a WHERE clause that mentions both vars
 * belonging to this relation and vars belonging to relations not yet
 * joined to it.)  We group these clauses according to the set of
 * other base relations (unjoined relations) mentioned in them.
 * There is one JoinInfo for each distinct set of unjoined_relids,
 * and its jinfo_restrictinfo lists the clause(s) that use that set
 * of other relations.
 */

typedef struct JoinInfo
{
        NodeTag         type;
        Relids          unjoined_relids;        /* some rels not yet part of my RelOptInfo */
        List       *jinfo_restrictinfo;         /* relevant RestrictInfos */
} JoinInfo;

/*
 * Inner indexscan info.
 *
 * An inner indexscan is one that uses one or more joinclauses as index
 * conditions (perhaps in addition to plain restriction clauses).  So it
 * can only be used as the inner path of a nestloop join where the outer
 * relation includes all other relids appearing in those joinclauses.
 * The set of usable joinclauses, and thus the best inner indexscan,
 * thus varies depending on which outer relation we consider; so we have
 * to recompute the best such path for every join.      To avoid lots of
 * redundant computation, we cache the results of such searches.  For
 * each index we compute the set of possible otherrelids (all relids
 * appearing in joinquals that could become indexquals for this index).
 * Two outer relations whose relids have the same intersection with this
 * set will have the same set of available joinclauses and thus the same
 * best inner indexscan for that index.  Similarly, for each base relation,
 * we form the union of the per-index otherrelids sets.  Two outer relations
 * with the same intersection with that set will have the same best overall
 * inner indexscan for the base relation.  We use lists of InnerIndexscanInfo
 * nodes to cache the results of these searches at both the index and
 * relation level.
 *
 * The search key also includes a bool showing whether the join being
 * considered is an outer join.  Since we constrain the join order for
 * outer joins, I believe that this bool can only have one possible value
 * for any particular base relation; but store it anyway to avoid confusion.
 */

typedef struct InnerIndexscanInfo
{
        NodeTag         type;
        /* The lookup key: */
        Relids          other_relids;   /* a set of relevant other relids */
        bool            isouterjoin;    /* true if join is outer */
        /* Best path for this lookup key: */
        Path       *best_innerpath; /* best inner indexscan, or NULL if none */
} InnerIndexscanInfo;

/*
 * IN clause info.
 *
 * When we convert top-level IN quals into join operations, we must restrict
 * the order of joining and use special join methods at some join points.
 * We record information about each such IN clause in an InClauseInfo struct.
 * These structs are kept in the Query node's in_info_list.
 */

typedef struct InClauseInfo
{
        NodeTag         type;
        Relids          lefthand;               /* base relids in lefthand expressions */
        Relids          righthand;              /* base relids coming from the subselect */
        List       *sub_targetlist; /* targetlist of original RHS subquery */

        /*
         * Note: sub_targetlist is just a list of Vars or expressions; it does
         * not contain TargetEntry nodes.
         */
} InClauseInfo;

#endif   /* RELATION_H */