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605 lines
18 KiB
C
605 lines
18 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) 1996-2005, 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 1.76 2005/10/15 02:49:20 momjian 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 is_inside_IN(PlannerInfo *root, RelOptInfo *rel);
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/*
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* make_rels_by_joins
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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 make_one_rel_by_joins.) 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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make_rels_by_joins(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)
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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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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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* An exception occurs when there is a clauseless join inside an
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* IN (sub-SELECT) construct. Here, the members of the subselect
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* all have join clauses (against the stuff outside the IN), but
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* they *must* be joined to each other before we can make use of
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* those join clauses. So do the clauseless join bit.
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*
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* See also the last-ditch case below.
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*/
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if (new_rels == NIL && is_inside_IN(root, old_rel))
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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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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. 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, in order to avoid unreasonable growth of planning
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* 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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if (old_rel->joininfo == NIL)
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continue; /* we ignore clauseless joins here */
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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.
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*/
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if (have_relevant_joinclause(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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JOIN_INNER);
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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 IN clauses are involved, there may be no legal way to make
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* 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 make_join_rel() 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 IN clauses then make_join_rel() 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->in_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 are mentioned within old_rel's joininfo list (i.e., relations
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* that participate in join clauses that 'old_rel' also participates in).
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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(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, JOIN_INNER);
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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, JOIN_INNER);
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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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* is_inside_IN
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* Detect whether the specified relation is inside an IN (sub-SELECT).
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*
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* Note that we are actually only interested in rels that have been pulled up
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* out of an IN, so the routine name is a slight misnomer.
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*/
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static bool
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is_inside_IN(PlannerInfo *root, RelOptInfo *rel)
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{
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ListCell *l;
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foreach(l, root->in_info_list)
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{
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InClauseInfo *ininfo = (InClauseInfo *) lfirst(l);
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if (bms_is_subset(rel->relids, ininfo->righthand))
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return true;
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}
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return false;
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}
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/*
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* make_jointree_rel
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* Find or build a RelOptInfo join rel representing a specific
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* jointree item. For JoinExprs, we only consider the construction
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* path that corresponds exactly to what the user wrote.
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*/
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RelOptInfo *
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make_jointree_rel(PlannerInfo *root, Node *jtnode)
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{
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if (IsA(jtnode, RangeTblRef))
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{
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int varno = ((RangeTblRef *) jtnode)->rtindex;
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return find_base_rel(root, varno);
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}
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else if (IsA(jtnode, FromExpr))
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{
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FromExpr *f = (FromExpr *) jtnode;
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/* Recurse back to multi-way-join planner */
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return make_fromexpr_rel(root, f);
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}
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else if (IsA(jtnode, JoinExpr))
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{
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JoinExpr *j = (JoinExpr *) jtnode;
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RelOptInfo *rel,
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*lrel,
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*rrel;
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/* Recurse */
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lrel = make_jointree_rel(root, j->larg);
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rrel = make_jointree_rel(root, j->rarg);
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/* Make this join rel */
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rel = make_join_rel(root, lrel, rrel, j->jointype);
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if (rel == NULL) /* oops */
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elog(ERROR, "invalid join order");
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/*
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* Since we are only going to consider this one way to do it, we're
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* done generating Paths for this joinrel and can now select the
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* cheapest. In fact we *must* do so now, since next level up will
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* need it!
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*/
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set_cheapest(rel);
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#ifdef OPTIMIZER_DEBUG
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debug_print_rel(root, rel);
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#endif
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return rel;
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}
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else
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elog(ERROR, "unrecognized node type: %d",
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(int) nodeTag(jtnode));
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return NULL; /* keep compiler quiet */
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}
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/*
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* make_join_rel
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* Find or create a join RelOptInfo that represents the join of
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* the two given rels, and add to it path information for paths
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* created with the two rels as outer and inner rel.
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* (The join rel may already contain paths generated from other
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* pairs of rels that add up to the same set of base rels.)
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*
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* NB: will return NULL if attempted join is not valid. This can only
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* happen when working with IN clauses that have been turned into joins.
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*/
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RelOptInfo *
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make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
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JoinType jointype)
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{
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Relids joinrelids;
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RelOptInfo *joinrel;
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List *restrictlist;
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/* We should never try to join two overlapping sets of rels. */
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Assert(!bms_overlap(rel1->relids, rel2->relids));
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/* Construct Relids set that identifies the joinrel. */
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joinrelids = bms_union(rel1->relids, rel2->relids);
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/*
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* If we are implementing IN clauses as joins, there are some joins that
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* are illegal. Check to see if the proposed join is trouble. We can skip
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* the work if looking at an outer join, however, because only top-level
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* joins might be affected.
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*/
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if (jointype == JOIN_INNER)
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{
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ListCell *l;
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foreach(l, root->in_info_list)
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{
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InClauseInfo *ininfo = (InClauseInfo *) lfirst(l);
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/*
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* This IN clause 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 INs quickly.)
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*/
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if (!bms_overlap(ininfo->righthand, joinrelids))
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continue;
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/*
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* If we are still building the IN clause's RHS, then this IN
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* clause isn't relevant yet.
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*/
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if (bms_is_subset(joinrelids, ininfo->righthand))
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continue;
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/*
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* Cannot join if proposed join contains rels not in the RHS *and*
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* contains only part of the RHS. We must build the complete RHS
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* (subselect's join) before it can be joined to rels outside the
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* subselect.
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*/
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if (!bms_is_subset(ininfo->righthand, joinrelids))
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{
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bms_free(joinrelids);
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return NULL;
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}
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/*
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* At this point we are considering a join of the IN's RHS to some
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* other rel(s).
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*
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* If we already joined IN's RHS to any other rels in either input
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* path, then this join is not constrained (the necessary work was
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* done at the lower level where that join occurred).
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*/
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if (bms_is_subset(ininfo->righthand, rel1->relids) &&
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!bms_equal(ininfo->righthand, rel1->relids))
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continue;
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if (bms_is_subset(ininfo->righthand, rel2->relids) &&
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!bms_equal(ininfo->righthand, rel2->relids))
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continue;
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/*
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* JOIN_IN technique will work if outerrel includes LHS and
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* innerrel is exactly RHS; conversely JOIN_REVERSE_IN handles
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* RHS/LHS.
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*
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* JOIN_UNIQUE_OUTER will work if outerrel is exactly RHS; conversely
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* JOIN_UNIQUE_INNER will work if innerrel is exactly RHS.
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*
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* But none of these will work if we already found another IN that
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* needs to trigger here.
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*/
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if (jointype != JOIN_INNER)
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{
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bms_free(joinrelids);
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return NULL;
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}
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if (bms_is_subset(ininfo->lefthand, rel1->relids) &&
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bms_equal(ininfo->righthand, rel2->relids))
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jointype = JOIN_IN;
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else if (bms_is_subset(ininfo->lefthand, rel2->relids) &&
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bms_equal(ininfo->righthand, rel1->relids))
|
|
jointype = JOIN_REVERSE_IN;
|
|
else if (bms_equal(ininfo->righthand, rel1->relids))
|
|
jointype = JOIN_UNIQUE_OUTER;
|
|
else if (bms_equal(ininfo->righthand, rel2->relids))
|
|
jointype = JOIN_UNIQUE_INNER;
|
|
else
|
|
{
|
|
/* invalid join path */
|
|
bms_free(joinrelids);
|
|
return NULL;
|
|
}
|
|
}
|
|
}
|
|
|
|
/*
|
|
* Find or build the join RelOptInfo, and compute the restrictlist that
|
|
* goes with this particular joining.
|
|
*/
|
|
joinrel = build_join_rel(root, joinrelids, rel1, rel2, jointype,
|
|
&restrictlist);
|
|
|
|
/*
|
|
* Consider paths using each rel as both outer and inner.
|
|
*/
|
|
switch (jointype)
|
|
{
|
|
case JOIN_INNER:
|
|
add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_INNER,
|
|
restrictlist);
|
|
add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_INNER,
|
|
restrictlist);
|
|
break;
|
|
case JOIN_LEFT:
|
|
add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_LEFT,
|
|
restrictlist);
|
|
add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_RIGHT,
|
|
restrictlist);
|
|
break;
|
|
case JOIN_FULL:
|
|
add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_FULL,
|
|
restrictlist);
|
|
add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_FULL,
|
|
restrictlist);
|
|
break;
|
|
case JOIN_RIGHT:
|
|
add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_RIGHT,
|
|
restrictlist);
|
|
add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_LEFT,
|
|
restrictlist);
|
|
break;
|
|
case JOIN_IN:
|
|
add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_IN,
|
|
restrictlist);
|
|
/* REVERSE_IN isn't supported by joinpath.c */
|
|
add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_UNIQUE_INNER,
|
|
restrictlist);
|
|
add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_UNIQUE_OUTER,
|
|
restrictlist);
|
|
break;
|
|
case JOIN_REVERSE_IN:
|
|
/* REVERSE_IN isn't supported by joinpath.c */
|
|
add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_IN,
|
|
restrictlist);
|
|
add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_UNIQUE_OUTER,
|
|
restrictlist);
|
|
add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_UNIQUE_INNER,
|
|
restrictlist);
|
|
break;
|
|
case JOIN_UNIQUE_OUTER:
|
|
add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_UNIQUE_OUTER,
|
|
restrictlist);
|
|
add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_UNIQUE_INNER,
|
|
restrictlist);
|
|
break;
|
|
case JOIN_UNIQUE_INNER:
|
|
add_paths_to_joinrel(root, joinrel, rel1, rel2, JOIN_UNIQUE_INNER,
|
|
restrictlist);
|
|
add_paths_to_joinrel(root, joinrel, rel2, rel1, JOIN_UNIQUE_OUTER,
|
|
restrictlist);
|
|
break;
|
|
default:
|
|
elog(ERROR, "unrecognized join type: %d",
|
|
(int) jointype);
|
|
break;
|
|
}
|
|
|
|
bms_free(joinrelids);
|
|
|
|
return joinrel;
|
|
}
|