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RHS that can't be unique-ified --- join_is_legal has to check that before deciding to build a join, else we'll have an unimplementable joinrel. Per report from Greg Stark.
970 lines
29 KiB
C
970 lines
29 KiB
C
/*-------------------------------------------------------------------------
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*
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* joinrels.c
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* Routines to determine which relations should be joined
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*
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* Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/optimizer/path/joinrels.c,v 1.96 2008/11/28 19:29:07 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "optimizer/joininfo.h"
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#include "optimizer/pathnode.h"
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#include "optimizer/paths.h"
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static List *make_rels_by_clause_joins(PlannerInfo *root,
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RelOptInfo *old_rel,
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ListCell *other_rels);
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static List *make_rels_by_clauseless_joins(PlannerInfo *root,
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RelOptInfo *old_rel,
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ListCell *other_rels);
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static bool has_join_restriction(PlannerInfo *root, RelOptInfo *rel);
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static bool has_legal_joinclause(PlannerInfo *root, RelOptInfo *rel);
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static bool is_dummy_rel(RelOptInfo *rel);
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static void mark_dummy_rel(RelOptInfo *rel);
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static bool restriction_is_constant_false(List *restrictlist);
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/*
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* join_search_one_level
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* Consider ways to produce join relations containing exactly 'level'
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* jointree items. (This is one step of the dynamic-programming method
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* embodied in standard_join_search.) Join rel nodes for each feasible
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* combination of lower-level rels are created and returned in a list.
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* Implementation paths are created for each such joinrel, too.
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*
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* level: level of rels we want to make this time.
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* joinrels[j], 1 <= j < level, is a list of rels containing j items.
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*/
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List *
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join_search_one_level(PlannerInfo *root, int level, List **joinrels)
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{
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List *result_rels = NIL;
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List *new_rels;
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ListCell *r;
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int k;
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/*
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* First, consider left-sided and right-sided plans, in which rels of
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* exactly level-1 member relations are joined against initial relations.
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* We prefer to join using join clauses, but if we find a rel of level-1
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* members that has no join clauses, we will generate Cartesian-product
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* joins against all initial rels not already contained in it.
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*
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* In the first pass (level == 2), we try to join each initial rel to each
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* initial rel that appears later in joinrels[1]. (The mirror-image joins
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* are handled automatically by make_join_rel.) In later passes, we try
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* to join rels of size level-1 from joinrels[level-1] to each initial rel
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* in joinrels[1].
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*/
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foreach(r, joinrels[level - 1])
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{
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RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
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ListCell *other_rels;
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if (level == 2)
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other_rels = lnext(r); /* only consider remaining initial
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* rels */
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else
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other_rels = list_head(joinrels[1]); /* consider all initial
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* rels */
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if (old_rel->joininfo != NIL || old_rel->has_eclass_joins ||
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has_join_restriction(root, old_rel))
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{
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/*
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* Note that if all available join clauses for this rel require
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* more than one other rel, we will fail to make any joins against
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* it here. In most cases that's OK; it'll be considered by
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* "bushy plan" join code in a higher-level pass where we have
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* those other rels collected into a join rel.
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*
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* See also the last-ditch case below.
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*/
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new_rels = make_rels_by_clause_joins(root,
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old_rel,
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other_rels);
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}
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else
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{
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/*
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* Oops, we have a relation that is not joined to any other
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* relation, either directly or by join-order restrictions.
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* Cartesian product time.
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*/
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new_rels = make_rels_by_clauseless_joins(root,
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old_rel,
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other_rels);
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}
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/*
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* At levels above 2 we will generate the same joined relation in
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* multiple ways --- for example (a join b) join c is the same
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* RelOptInfo as (b join c) join a, though the second case will add a
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* different set of Paths to it. To avoid making extra work for
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* subsequent passes, do not enter the same RelOptInfo into our output
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* list multiple times.
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*/
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result_rels = list_concat_unique_ptr(result_rels, new_rels);
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}
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/*
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* Now, consider "bushy plans" in which relations of k initial rels are
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* joined to relations of level-k initial rels, for 2 <= k <= level-2.
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*
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* We only consider bushy-plan joins for pairs of rels where there is a
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* suitable join clause (or join order restriction), in order to avoid
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* unreasonable growth of planning time.
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*/
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for (k = 2;; k++)
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{
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int other_level = level - k;
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/*
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* Since make_join_rel(x, y) handles both x,y and y,x cases, we only
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* need to go as far as the halfway point.
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*/
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if (k > other_level)
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break;
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foreach(r, joinrels[k])
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{
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RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
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ListCell *other_rels;
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ListCell *r2;
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/*
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* We can ignore clauseless joins here, *except* when they
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* participate in join-order restrictions --- then we might have
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* to force a bushy join plan.
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*/
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if (old_rel->joininfo == NIL && !old_rel->has_eclass_joins &&
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!has_join_restriction(root, old_rel))
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continue;
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if (k == other_level)
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other_rels = lnext(r); /* only consider remaining rels */
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else
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other_rels = list_head(joinrels[other_level]);
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for_each_cell(r2, other_rels)
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{
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RelOptInfo *new_rel = (RelOptInfo *) lfirst(r2);
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if (!bms_overlap(old_rel->relids, new_rel->relids))
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{
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/*
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* OK, we can build a rel of the right level from this
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* pair of rels. Do so if there is at least one usable
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* join clause or a relevant join restriction.
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*/
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if (have_relevant_joinclause(root, old_rel, new_rel) ||
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have_join_order_restriction(root, old_rel, new_rel))
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{
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RelOptInfo *jrel;
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jrel = make_join_rel(root, old_rel, new_rel);
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/* Avoid making duplicate entries ... */
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if (jrel)
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result_rels = list_append_unique_ptr(result_rels,
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jrel);
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}
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}
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}
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}
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}
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/*
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* Last-ditch effort: if we failed to find any usable joins so far, force
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* a set of cartesian-product joins to be generated. This handles the
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* special case where all the available rels have join clauses but we
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* cannot use any of the joins yet. An example is
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*
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* SELECT * FROM a,b,c WHERE (a.f1 + b.f2 + c.f3) = 0;
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*
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* The join clause will be usable at level 3, but at level 2 we have no
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* choice but to make cartesian joins. We consider only left-sided and
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* right-sided cartesian joins in this case (no bushy).
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*/
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if (result_rels == NIL)
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{
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/*
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* This loop is just like the first one, except we always call
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* make_rels_by_clauseless_joins().
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*/
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foreach(r, joinrels[level - 1])
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{
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RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
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ListCell *other_rels;
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if (level == 2)
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other_rels = lnext(r); /* only consider remaining initial
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* rels */
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else
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other_rels = list_head(joinrels[1]); /* consider all initial
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* rels */
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new_rels = make_rels_by_clauseless_joins(root,
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old_rel,
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other_rels);
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result_rels = list_concat_unique_ptr(result_rels, new_rels);
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}
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/*----------
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* When special joins are involved, there may be no legal way
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* to make an N-way join for some values of N. For example consider
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*
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* SELECT ... FROM t1 WHERE
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* x IN (SELECT ... FROM t2,t3 WHERE ...) AND
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* y IN (SELECT ... FROM t4,t5 WHERE ...)
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*
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* We will flatten this query to a 5-way join problem, but there are
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* no 4-way joins that join_is_legal() will consider legal. We have
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* to accept failure at level 4 and go on to discover a workable
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* bushy plan at level 5.
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*
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* However, if there are no special joins then join_is_legal() should
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* never fail, and so the following sanity check is useful.
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*----------
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*/
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if (result_rels == NIL && root->join_info_list == NIL)
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elog(ERROR, "failed to build any %d-way joins", level);
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}
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return result_rels;
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}
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/*
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* make_rels_by_clause_joins
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* Build joins between the given relation 'old_rel' and other relations
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* that participate in join clauses that 'old_rel' also participates in
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* (or participate in join-order restrictions with it).
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* The join rel nodes are returned in a list.
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*
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* 'old_rel' is the relation entry for the relation to be joined
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* 'other_rels': the first cell in a linked list containing the other
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* rels to be considered for joining
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*
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* Currently, this is only used with initial rels in other_rels, but it
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* will work for joining to joinrels too.
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*/
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static List *
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make_rels_by_clause_joins(PlannerInfo *root,
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RelOptInfo *old_rel,
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ListCell *other_rels)
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{
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List *result = NIL;
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ListCell *l;
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for_each_cell(l, other_rels)
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{
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RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
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if (!bms_overlap(old_rel->relids, other_rel->relids) &&
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(have_relevant_joinclause(root, old_rel, other_rel) ||
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have_join_order_restriction(root, old_rel, other_rel)))
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{
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RelOptInfo *jrel;
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jrel = make_join_rel(root, old_rel, other_rel);
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if (jrel)
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result = lcons(jrel, result);
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}
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}
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return result;
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}
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/*
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* make_rels_by_clauseless_joins
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* Given a relation 'old_rel' and a list of other relations
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* 'other_rels', create a join relation between 'old_rel' and each
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* member of 'other_rels' that isn't already included in 'old_rel'.
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* The join rel nodes are returned in a list.
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*
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* 'old_rel' is the relation entry for the relation to be joined
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* 'other_rels': the first cell of a linked list containing the
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* other rels to be considered for joining
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*
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* Currently, this is only used with initial rels in other_rels, but it would
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* work for joining to joinrels too.
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*/
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static List *
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make_rels_by_clauseless_joins(PlannerInfo *root,
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RelOptInfo *old_rel,
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ListCell *other_rels)
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{
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List *result = NIL;
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ListCell *i;
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for_each_cell(i, other_rels)
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{
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RelOptInfo *other_rel = (RelOptInfo *) lfirst(i);
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if (!bms_overlap(other_rel->relids, old_rel->relids))
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{
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RelOptInfo *jrel;
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jrel = make_join_rel(root, old_rel, other_rel);
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/*
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* As long as given other_rels are distinct, don't need to test to
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* see if jrel is already part of output list.
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*/
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if (jrel)
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result = lcons(jrel, result);
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}
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}
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return result;
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}
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/*
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* join_is_legal
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* Determine whether a proposed join is legal given the query's
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* join order constraints; and if it is, determine the join type.
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*
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* Caller must supply not only the two rels, but the union of their relids.
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* (We could simplify the API by computing joinrelids locally, but this
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* would be redundant work in the normal path through make_join_rel.)
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*
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* On success, *sjinfo_p is set to NULL if this is to be a plain inner join,
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* else it's set to point to the associated SpecialJoinInfo node. Also,
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* *reversed_p is set TRUE if the given relations need to be swapped to
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* match the SpecialJoinInfo node.
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*/
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static bool
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join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
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Relids joinrelids,
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SpecialJoinInfo **sjinfo_p, bool *reversed_p)
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{
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SpecialJoinInfo *match_sjinfo;
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bool reversed;
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bool is_valid_inner;
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ListCell *l;
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/*
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* Ensure output params are set on failure return. This is just to
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* suppress uninitialized-variable warnings from overly anal compilers.
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*/
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*sjinfo_p = NULL;
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*reversed_p = false;
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/*
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* If we have any special joins, the proposed join might be illegal; and
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* in any case we have to determine its join type. Scan the join info
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* list for conflicts.
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*/
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match_sjinfo = NULL;
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reversed = false;
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is_valid_inner = true;
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foreach(l, root->join_info_list)
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{
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SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
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/*
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* This special join is not relevant unless its RHS overlaps the
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* proposed join. (Check this first as a fast path for dismissing
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* most irrelevant SJs quickly.)
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*/
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if (!bms_overlap(sjinfo->min_righthand, joinrelids))
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continue;
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/*
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* Also, not relevant if proposed join is fully contained within RHS
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* (ie, we're still building up the RHS).
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*/
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if (bms_is_subset(joinrelids, sjinfo->min_righthand))
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continue;
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/*
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* Also, not relevant if SJ is already done within either input.
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*/
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if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
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bms_is_subset(sjinfo->min_righthand, rel1->relids))
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continue;
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if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
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bms_is_subset(sjinfo->min_righthand, rel2->relids))
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continue;
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/*
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* If one input contains min_lefthand and the other contains
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* min_righthand, then we can perform the SJ at this join.
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*
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* Barf if we get matches to more than one SJ (is that possible?)
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*/
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if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
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bms_is_subset(sjinfo->min_righthand, rel2->relids))
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{
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if (match_sjinfo)
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return false; /* invalid join path */
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match_sjinfo = sjinfo;
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reversed = false;
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}
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else if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
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bms_is_subset(sjinfo->min_righthand, rel1->relids))
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{
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if (match_sjinfo)
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return false; /* invalid join path */
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match_sjinfo = sjinfo;
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reversed = true;
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}
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else if (sjinfo->jointype == JOIN_SEMI &&
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bms_equal(sjinfo->syn_righthand, rel2->relids) &&
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create_unique_path(root, rel2, rel2->cheapest_total_path,
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sjinfo) != NULL)
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{
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/*
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* For a semijoin, we can join the RHS to anything else by
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* unique-ifying the RHS (if the RHS can be unique-ified).
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*/
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if (match_sjinfo)
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return false; /* invalid join path */
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match_sjinfo = sjinfo;
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reversed = false;
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}
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else if (sjinfo->jointype == JOIN_SEMI &&
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bms_equal(sjinfo->syn_righthand, rel1->relids) &&
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create_unique_path(root, rel1, rel1->cheapest_total_path,
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sjinfo) != NULL)
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{
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/* Reversed semijoin case */
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if (match_sjinfo)
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return false; /* invalid join path */
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match_sjinfo = sjinfo;
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reversed = true;
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}
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else
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{
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/*----------
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* Otherwise, the proposed join overlaps the RHS but isn't
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* a valid implementation of this SJ. It might still be
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* a legal join, however. If both inputs overlap the RHS,
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* assume that it's OK. Since the inputs presumably got past
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* this function's checks previously, they can't overlap the
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* LHS and their violations of the RHS boundary must represent
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* SJs that have been determined to commute with this one.
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* We have to allow this to work correctly in cases like
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* (a LEFT JOIN (b JOIN (c LEFT JOIN d)))
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* when the c/d join has been determined to commute with the join
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* to a, and hence d is not part of min_righthand for the upper
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* join. It should be legal to join b to c/d but this will appear
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* as a violation of the upper join's RHS.
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* Furthermore, if one input overlaps the RHS and the other does
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* not, we should still allow the join if it is a valid
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* implementation of some other SJ. We have to allow this to
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* support the associative identity
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* (a LJ b on Pab) LJ c ON Pbc = a LJ (b LJ c ON Pbc) on Pab
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* since joining B directly to C violates the lower SJ's RHS.
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* We assume that make_outerjoininfo() set things up correctly
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* so that we'll only match to some SJ if the join is valid.
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* Set flag here to check at bottom of loop.
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*
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* For a semijoin, assume it's okay if either side fully contains
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* the RHS (per the unique-ification case above).
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*----------
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*/
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if (sjinfo->jointype != JOIN_SEMI &&
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bms_overlap(rel1->relids, sjinfo->min_righthand) &&
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bms_overlap(rel2->relids, sjinfo->min_righthand))
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{
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/* seems OK */
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Assert(!bms_overlap(joinrelids, sjinfo->min_lefthand));
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}
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else if (sjinfo->jointype == JOIN_SEMI &&
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(bms_is_subset(sjinfo->syn_righthand, rel1->relids) ||
|
|
bms_is_subset(sjinfo->syn_righthand, rel2->relids)))
|
|
{
|
|
/* seems OK */
|
|
}
|
|
else
|
|
is_valid_inner = false;
|
|
}
|
|
}
|
|
|
|
/* Fail if violated some SJ's RHS and didn't match to another SJ */
|
|
if (match_sjinfo == NULL && !is_valid_inner)
|
|
return false; /* invalid join path */
|
|
|
|
/* Otherwise, it's a valid join */
|
|
*sjinfo_p = match_sjinfo;
|
|
*reversed_p = reversed;
|
|
return true;
|
|
}
|
|
|
|
|
|
/*
|
|
* make_join_rel
|
|
* Find or create a join RelOptInfo that represents the join of
|
|
* the two given rels, and add to it path information for paths
|
|
* created with the two rels as outer and inner rel.
|
|
* (The join rel may already contain paths generated from other
|
|
* pairs of rels that add up to the same set of base rels.)
|
|
*
|
|
* NB: will return NULL if attempted join is not valid. This can happen
|
|
* when working with outer joins, or with IN or EXISTS clauses that have been
|
|
* turned into joins.
|
|
*/
|
|
RelOptInfo *
|
|
make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2)
|
|
{
|
|
Relids joinrelids;
|
|
SpecialJoinInfo *sjinfo;
|
|
bool reversed;
|
|
SpecialJoinInfo sjinfo_data;
|
|
RelOptInfo *joinrel;
|
|
List *restrictlist;
|
|
|
|
/* We should never try to join two overlapping sets of rels. */
|
|
Assert(!bms_overlap(rel1->relids, rel2->relids));
|
|
|
|
/* Construct Relids set that identifies the joinrel. */
|
|
joinrelids = bms_union(rel1->relids, rel2->relids);
|
|
|
|
/* Check validity and determine join type. */
|
|
if (!join_is_legal(root, rel1, rel2, joinrelids,
|
|
&sjinfo, &reversed))
|
|
{
|
|
/* invalid join path */
|
|
bms_free(joinrelids);
|
|
return NULL;
|
|
}
|
|
|
|
/* Swap rels if needed to match the join info. */
|
|
if (reversed)
|
|
{
|
|
RelOptInfo *trel = rel1;
|
|
|
|
rel1 = rel2;
|
|
rel2 = trel;
|
|
}
|
|
|
|
/*
|
|
* If it's a plain inner join, then we won't have found anything in
|
|
* join_info_list. Make up a SpecialJoinInfo so that selectivity
|
|
* estimation functions will know what's being joined.
|
|
*/
|
|
if (sjinfo == NULL)
|
|
{
|
|
sjinfo = &sjinfo_data;
|
|
sjinfo->type = T_SpecialJoinInfo;
|
|
sjinfo->min_lefthand = rel1->relids;
|
|
sjinfo->min_righthand = rel2->relids;
|
|
sjinfo->syn_lefthand = rel1->relids;
|
|
sjinfo->syn_righthand = rel2->relids;
|
|
sjinfo->jointype = JOIN_INNER;
|
|
/* we don't bother trying to make the remaining fields valid */
|
|
sjinfo->lhs_strict = false;
|
|
sjinfo->delay_upper_joins = false;
|
|
sjinfo->join_quals = NIL;
|
|
}
|
|
|
|
/*
|
|
* Find or build the join RelOptInfo, and compute the restrictlist that
|
|
* goes with this particular joining.
|
|
*/
|
|
joinrel = build_join_rel(root, joinrelids, rel1, rel2, sjinfo,
|
|
&restrictlist);
|
|
|
|
/*
|
|
* If we've already proven this join is empty, we needn't consider
|
|
* any more paths for it.
|
|
*/
|
|
if (is_dummy_rel(joinrel))
|
|
{
|
|
bms_free(joinrelids);
|
|
return joinrel;
|
|
}
|
|
|
|
/*
|
|
* Consider paths using each rel as both outer and inner. Depending
|
|
* on the join type, a provably empty outer or inner rel might mean
|
|
* the join is provably empty too; in which case throw away any
|
|
* previously computed paths and mark the join as dummy. (We do it
|
|
* this way since it's conceivable that dummy-ness of a multi-element
|
|
* join might only be noticeable for certain construction paths.)
|
|
*
|
|
* Also, a provably constant-false join restriction typically means that
|
|
* we can skip evaluating one or both sides of the join. We do this
|
|
* by marking the appropriate rel as dummy.
|
|
*
|
|
* We need only consider the jointypes that appear in join_info_list,
|
|
* plus JOIN_INNER.
|
|
*/
|
|
switch (sjinfo->jointype)
|
|
{
|
|
case JOIN_INNER:
|
|
if (is_dummy_rel(rel1) || is_dummy_rel(rel2) ||
|
|
restriction_is_constant_false(restrictlist))
|
|
{
|
|
mark_dummy_rel(joinrel);
|
|
break;
|
|
}
|
|
add_paths_to_joinrel(root, joinrel, rel1, rel2,
|
|
JOIN_INNER, sjinfo,
|
|
restrictlist);
|
|
add_paths_to_joinrel(root, joinrel, rel2, rel1,
|
|
JOIN_INNER, sjinfo,
|
|
restrictlist);
|
|
break;
|
|
case JOIN_LEFT:
|
|
if (is_dummy_rel(rel1))
|
|
{
|
|
mark_dummy_rel(joinrel);
|
|
break;
|
|
}
|
|
if (restriction_is_constant_false(restrictlist) &&
|
|
bms_is_subset(rel2->relids, sjinfo->syn_righthand))
|
|
mark_dummy_rel(rel2);
|
|
add_paths_to_joinrel(root, joinrel, rel1, rel2,
|
|
JOIN_LEFT, sjinfo,
|
|
restrictlist);
|
|
add_paths_to_joinrel(root, joinrel, rel2, rel1,
|
|
JOIN_RIGHT, sjinfo,
|
|
restrictlist);
|
|
break;
|
|
case JOIN_FULL:
|
|
if (is_dummy_rel(rel1) && is_dummy_rel(rel2))
|
|
{
|
|
mark_dummy_rel(joinrel);
|
|
break;
|
|
}
|
|
add_paths_to_joinrel(root, joinrel, rel1, rel2,
|
|
JOIN_FULL, sjinfo,
|
|
restrictlist);
|
|
add_paths_to_joinrel(root, joinrel, rel2, rel1,
|
|
JOIN_FULL, sjinfo,
|
|
restrictlist);
|
|
break;
|
|
case JOIN_SEMI:
|
|
/*
|
|
* Do these steps only if we actually have a regular semijoin,
|
|
* as opposed to a case where we should unique-ify the RHS.
|
|
*/
|
|
if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
|
|
bms_is_subset(sjinfo->min_righthand, rel2->relids))
|
|
{
|
|
if (is_dummy_rel(rel1) || is_dummy_rel(rel2) ||
|
|
restriction_is_constant_false(restrictlist))
|
|
{
|
|
mark_dummy_rel(joinrel);
|
|
break;
|
|
}
|
|
add_paths_to_joinrel(root, joinrel, rel1, rel2,
|
|
JOIN_SEMI, sjinfo,
|
|
restrictlist);
|
|
}
|
|
|
|
/*
|
|
* If we know how to unique-ify the RHS and one input rel is
|
|
* exactly the RHS (not a superset) we can consider unique-ifying
|
|
* it and then doing a regular join. (The create_unique_path
|
|
* check here is probably redundant with what join_is_legal did,
|
|
* but if so the check is cheap because it's cached. So test
|
|
* anyway to be sure.)
|
|
*/
|
|
if (bms_equal(sjinfo->syn_righthand, rel2->relids) &&
|
|
create_unique_path(root, rel2, rel2->cheapest_total_path,
|
|
sjinfo) != NULL)
|
|
{
|
|
add_paths_to_joinrel(root, joinrel, rel1, rel2,
|
|
JOIN_UNIQUE_INNER, sjinfo,
|
|
restrictlist);
|
|
add_paths_to_joinrel(root, joinrel, rel2, rel1,
|
|
JOIN_UNIQUE_OUTER, sjinfo,
|
|
restrictlist);
|
|
}
|
|
break;
|
|
case JOIN_ANTI:
|
|
if (is_dummy_rel(rel1))
|
|
{
|
|
mark_dummy_rel(joinrel);
|
|
break;
|
|
}
|
|
if (restriction_is_constant_false(restrictlist) &&
|
|
bms_is_subset(rel2->relids, sjinfo->syn_righthand))
|
|
mark_dummy_rel(rel2);
|
|
add_paths_to_joinrel(root, joinrel, rel1, rel2,
|
|
JOIN_ANTI, sjinfo,
|
|
restrictlist);
|
|
break;
|
|
default:
|
|
/* other values not expected here */
|
|
elog(ERROR, "unrecognized join type: %d", (int) sjinfo->jointype);
|
|
break;
|
|
}
|
|
|
|
bms_free(joinrelids);
|
|
|
|
return joinrel;
|
|
}
|
|
|
|
|
|
/*
|
|
* have_join_order_restriction
|
|
* Detect whether the two relations should be joined to satisfy
|
|
* a join-order restriction arising from special joins.
|
|
*
|
|
* In practice this is always used with have_relevant_joinclause(), and so
|
|
* could be merged with that function, but it seems clearer to separate the
|
|
* two concerns. We need these tests because there are degenerate cases where
|
|
* a clauseless join must be performed to satisfy join-order restrictions.
|
|
*
|
|
* Note: this is only a problem if one side of a degenerate outer join
|
|
* contains multiple rels, or a clauseless join is required within an
|
|
* IN/EXISTS RHS; else we will find a join path via the "last ditch" case in
|
|
* join_search_one_level(). We could dispense with this test if we were
|
|
* willing to try bushy plans in the "last ditch" case, but that seems much
|
|
* less efficient.
|
|
*/
|
|
bool
|
|
have_join_order_restriction(PlannerInfo *root,
|
|
RelOptInfo *rel1, RelOptInfo *rel2)
|
|
{
|
|
bool result = false;
|
|
ListCell *l;
|
|
|
|
/*
|
|
* It's possible that the rels correspond to the left and right sides of a
|
|
* degenerate outer join, that is, one with no joinclause mentioning the
|
|
* non-nullable side; in which case we should force the join to occur.
|
|
*
|
|
* Also, the two rels could represent a clauseless join that has to be
|
|
* completed to build up the LHS or RHS of an outer join.
|
|
*/
|
|
foreach(l, root->join_info_list)
|
|
{
|
|
SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
|
|
|
|
/* ignore full joins --- other mechanisms handle them */
|
|
if (sjinfo->jointype == JOIN_FULL)
|
|
continue;
|
|
|
|
/* Can we perform the SJ with these rels? */
|
|
if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
|
|
bms_is_subset(sjinfo->min_righthand, rel2->relids))
|
|
{
|
|
result = true;
|
|
break;
|
|
}
|
|
if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
|
|
bms_is_subset(sjinfo->min_righthand, rel1->relids))
|
|
{
|
|
result = true;
|
|
break;
|
|
}
|
|
|
|
/*
|
|
* Might we need to join these rels to complete the RHS? We have to
|
|
* use "overlap" tests since either rel might include a lower SJ that
|
|
* has been proven to commute with this one.
|
|
*/
|
|
if (bms_overlap(sjinfo->min_righthand, rel1->relids) &&
|
|
bms_overlap(sjinfo->min_righthand, rel2->relids))
|
|
{
|
|
result = true;
|
|
break;
|
|
}
|
|
|
|
/* Likewise for the LHS. */
|
|
if (bms_overlap(sjinfo->min_lefthand, rel1->relids) &&
|
|
bms_overlap(sjinfo->min_lefthand, rel2->relids))
|
|
{
|
|
result = true;
|
|
break;
|
|
}
|
|
}
|
|
|
|
/*
|
|
* We do not force the join to occur if either input rel can legally be
|
|
* joined to anything else using joinclauses. This essentially means that
|
|
* clauseless bushy joins are put off as long as possible. The reason is
|
|
* that when there is a join order restriction high up in the join tree
|
|
* (that is, with many rels inside the LHS or RHS), we would otherwise
|
|
* expend lots of effort considering very stupid join combinations within
|
|
* its LHS or RHS.
|
|
*/
|
|
if (result)
|
|
{
|
|
if (has_legal_joinclause(root, rel1) ||
|
|
has_legal_joinclause(root, rel2))
|
|
result = false;
|
|
}
|
|
|
|
return result;
|
|
}
|
|
|
|
|
|
/*
|
|
* has_join_restriction
|
|
* Detect whether the specified relation has join-order restrictions
|
|
* due to being inside an outer join or an IN (sub-SELECT).
|
|
*
|
|
* Essentially, this tests whether have_join_order_restriction() could
|
|
* succeed with this rel and some other one. It's OK if we sometimes
|
|
* say "true" incorrectly. (Therefore, we don't bother with the relatively
|
|
* expensive has_legal_joinclause test.)
|
|
*/
|
|
static bool
|
|
has_join_restriction(PlannerInfo *root, RelOptInfo *rel)
|
|
{
|
|
ListCell *l;
|
|
|
|
foreach(l, root->join_info_list)
|
|
{
|
|
SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
|
|
|
|
/* ignore full joins --- other mechanisms preserve their ordering */
|
|
if (sjinfo->jointype == JOIN_FULL)
|
|
continue;
|
|
|
|
/* ignore if SJ is already contained in rel */
|
|
if (bms_is_subset(sjinfo->min_lefthand, rel->relids) &&
|
|
bms_is_subset(sjinfo->min_righthand, rel->relids))
|
|
continue;
|
|
|
|
/* restricted if it overlaps LHS or RHS, but doesn't contain SJ */
|
|
if (bms_overlap(sjinfo->min_lefthand, rel->relids) ||
|
|
bms_overlap(sjinfo->min_righthand, rel->relids))
|
|
return true;
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
|
|
/*
|
|
* has_legal_joinclause
|
|
* Detect whether the specified relation can legally be joined
|
|
* to any other rels using join clauses.
|
|
*
|
|
* We consider only joins to single other relations in the current
|
|
* initial_rels list. This is sufficient to get a "true" result in most real
|
|
* queries, and an occasional erroneous "false" will only cost a bit more
|
|
* planning time. The reason for this limitation is that considering joins to
|
|
* other joins would require proving that the other join rel can legally be
|
|
* formed, which seems like too much trouble for something that's only a
|
|
* heuristic to save planning time. (Note: we must look at initial_rels
|
|
* and not all of the query, since when we are planning a sub-joinlist we
|
|
* may be forced to make clauseless joins within initial_rels even though
|
|
* there are join clauses linking to other parts of the query.)
|
|
*/
|
|
static bool
|
|
has_legal_joinclause(PlannerInfo *root, RelOptInfo *rel)
|
|
{
|
|
ListCell *lc;
|
|
|
|
foreach(lc, root->initial_rels)
|
|
{
|
|
RelOptInfo *rel2 = (RelOptInfo *) lfirst(lc);
|
|
|
|
/* ignore rels that are already in "rel" */
|
|
if (bms_overlap(rel->relids, rel2->relids))
|
|
continue;
|
|
|
|
if (have_relevant_joinclause(root, rel, rel2))
|
|
{
|
|
Relids joinrelids;
|
|
SpecialJoinInfo *sjinfo;
|
|
bool reversed;
|
|
|
|
/* join_is_legal needs relids of the union */
|
|
joinrelids = bms_union(rel->relids, rel2->relids);
|
|
|
|
if (join_is_legal(root, rel, rel2, joinrelids,
|
|
&sjinfo, &reversed))
|
|
{
|
|
/* Yes, this will work */
|
|
bms_free(joinrelids);
|
|
return true;
|
|
}
|
|
|
|
bms_free(joinrelids);
|
|
}
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
|
|
/*
|
|
* is_dummy_rel --- has relation been proven empty?
|
|
*
|
|
* If so, it will have a single path that is dummy.
|
|
*/
|
|
static bool
|
|
is_dummy_rel(RelOptInfo *rel)
|
|
{
|
|
return (rel->cheapest_total_path != NULL &&
|
|
IS_DUMMY_PATH(rel->cheapest_total_path));
|
|
}
|
|
|
|
/*
|
|
* Mark a rel as proven empty.
|
|
*/
|
|
static void
|
|
mark_dummy_rel(RelOptInfo *rel)
|
|
{
|
|
/* Set dummy size estimate */
|
|
rel->rows = 0;
|
|
|
|
/* Evict any previously chosen paths */
|
|
rel->pathlist = NIL;
|
|
|
|
/* Set up the dummy path */
|
|
add_path(rel, (Path *) create_append_path(rel, NIL));
|
|
|
|
/* Set or update cheapest_total_path */
|
|
set_cheapest(rel);
|
|
}
|
|
|
|
|
|
/*
|
|
* restriction_is_constant_false --- is a restrictlist just FALSE?
|
|
*
|
|
* In cases where a qual is provably constant FALSE, eval_const_expressions
|
|
* will generally have thrown away anything that's ANDed with it. In outer
|
|
* join situations this will leave us computing cartesian products only to
|
|
* decide there's no match for an outer row, which is pretty stupid. So,
|
|
* we need to detect the case.
|
|
*/
|
|
static bool
|
|
restriction_is_constant_false(List *restrictlist)
|
|
{
|
|
ListCell *lc;
|
|
|
|
/*
|
|
* Despite the above comment, the restriction list we see here might
|
|
* possibly have other members besides the FALSE constant, since other
|
|
* quals could get "pushed down" to the outer join level. So we check
|
|
* each member of the list.
|
|
*/
|
|
foreach(lc, restrictlist)
|
|
{
|
|
RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
|
|
|
|
Assert(IsA(rinfo, RestrictInfo));
|
|
if (rinfo->clause && IsA(rinfo->clause, Const))
|
|
{
|
|
Const *con = (Const *) rinfo->clause;
|
|
|
|
/* constant NULL is as good as constant FALSE for our purposes */
|
|
if (con->constisnull)
|
|
return true;
|
|
if (!DatumGetBool(con->constvalue))
|
|
return true;
|
|
}
|
|
}
|
|
return false;
|
|
}
|