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cases where joinclauses were present but some joins have to be made by cartesian-product join anyway. An example is SELECT * FROM a,b,c WHERE (a.f1 + b.f2 + c.f3) = 0; Even though all the rels have joinclauses, we must join two of them in cartesian style before we can use the join clause...
328 lines
9.9 KiB
C
328 lines
9.9 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) 1996-2000, PostgreSQL, Inc
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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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* $Header: /cvsroot/pgsql/src/backend/optimizer/path/joinrels.c,v 1.45 2000/04/27 18:35:04 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/cost.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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#include "optimizer/tlist.h"
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static RelOptInfo *make_join_rel(Query *root, RelOptInfo *rel1,
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RelOptInfo *rel2);
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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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* base relations. (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 base rels are created and added to the front of the
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* query's join_rel_list. Implementation paths are created for each
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* such joinrel, too.
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*
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* Returns nothing, but adds entries to root->join_rel_list.
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*/
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void
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make_rels_by_joins(Query *root, int level)
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{
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List *first_old_rel = root->join_rel_list;
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List *r;
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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 base relations.
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* We prefer to join using join clauses, but if we find a rel of
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* level-1 members that has no join clauses, we will generate
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* Cartesian-product joins against all base rels not already contained
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* in it.
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*
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* In the first pass (level == 2), we try to join each base rel to each
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* base rel that appears later in base_rel_list. (The mirror-image
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* joins are handled automatically by make_join_rel.) In later
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* passes, we try to join rels of size level-1 from join_rel_list to
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* each base rel in base_rel_list.
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*
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* We assume that the rels already present in join_rel_list appear in
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* decreasing order of level (number of members). This should be true
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* since we always add new higher-level rels to the front of the list.
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*/
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if (level == 2)
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r = root->base_rel_list;/* level-1 is base rels */
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else
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r = root->join_rel_list;
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for (; r != NIL; r = lnext(r))
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{
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RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
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int old_level = length(old_rel->relids);
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List *other_rels;
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if (old_level != level - 1)
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break;
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if (level == 2)
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other_rels = lnext(r); /* only consider remaining base
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* rels */
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else
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other_rels = root->base_rel_list; /* consider all base 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
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* require more than one other rel, we will fail to make any
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* joins against it here. That's OK; it'll be considered by
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* "bushy plan" join code in a higher-level pass where we
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* have those other rels collected into a join rel. See also
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* the last-ditch case below.
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*/
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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. Cartesian product time.
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*/
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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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/*
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* Now, consider "bushy plans" in which relations of k base rels are
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* joined to relations of level-k base rels, for 2 <= k <= level-2.
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* The previous loop left r pointing to the first rel of level
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* 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
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* planning time.
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*/
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for (; r != NIL; r = lnext(r))
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{
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RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
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int old_level = length(old_rel->relids);
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List *r2;
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/*
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* We can quit once past the halfway point (make_join_rel took
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* care of making the opposite-direction joins)
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*/
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if (old_level * 2 < level)
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break;
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if (old_rel->joininfo == NIL)
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continue; /* we ignore clauseless joins here */
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foreach(r2, lnext(r))
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{
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RelOptInfo *new_rel = (RelOptInfo *) lfirst(r2);
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int new_level = length(new_rel->relids);
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if (old_level + new_level > level)
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continue; /* scan down to new_rels of right size */
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if (old_level + new_level < level)
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break; /* no more new_rels of right size */
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if (nonoverlap_setsi(old_rel->relids, new_rel->relids))
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{
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List *i;
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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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foreach(i, old_rel->joininfo)
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{
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JoinInfo *joininfo = (JoinInfo *) lfirst(i);
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if (is_subseti(joininfo->unjoined_relids, new_rel->relids))
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{
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make_join_rel(root, old_rel, new_rel);
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break;
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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,
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* force a set of cartesian-product joins to be generated. This
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* handles the special case where all the available rels have join
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* clauses but we 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
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* no choice but to make cartesian joins. We consider only left-sided
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* and right-sided cartesian joins in this case (no bushy).
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*/
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if (root->join_rel_list == first_old_rel)
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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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if (level == 2)
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r = root->base_rel_list; /* level-1 is base rels */
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else
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r = root->join_rel_list;
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for (; r != NIL; r = lnext(r))
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{
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RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
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int old_level = length(old_rel->relids);
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List *other_rels;
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if (old_level != level - 1)
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break;
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if (level == 2)
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other_rels = lnext(r); /* only consider remaining base
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* rels */
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else
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other_rels = root->base_rel_list; /* consider all base rels */
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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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if (root->join_rel_list == first_old_rel)
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elog(ERROR, "make_rels_by_joins: failed to build any %d-way joins",
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level);
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}
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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 nodes (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 added to root->join_rel_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': other rels to be considered for joining
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*
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* Currently, this is only used with base rels in other_rels, but it would
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* work for joining to joinrels too, if the caller ensures there is no
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* membership overlap between old_rel and the rels in other_rels. (We need
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* no extra test for overlap for base rels, since the is_subset test can
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* only succeed when other_rel is not already part of old_rel.)
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*
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* Returns NULL if no suitable joins were found, else the last suitable
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* joinrel processed. (The only caller who checks the return value is
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* geqo_eval.c, and it sets things up so there can be no more than one
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* "suitable" joinrel; so we don't bother with returning a list.)
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*/
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RelOptInfo *
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make_rels_by_clause_joins(Query *root,
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RelOptInfo *old_rel,
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List *other_rels)
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{
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RelOptInfo *result = NULL;
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List *i,
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*j;
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foreach(i, old_rel->joininfo)
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{
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JoinInfo *joininfo = (JoinInfo *) lfirst(i);
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Relids unjoined_relids = joininfo->unjoined_relids;
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foreach(j, other_rels)
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{
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RelOptInfo *other_rel = (RelOptInfo *) lfirst(j);
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if (is_subseti(unjoined_relids, other_rel->relids))
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result = make_join_rel(root, old_rel, other_rel);
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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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*
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* 'old_rel' is the relation entry for the relation to be joined
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* 'other_rels': other rels to be considered for joining
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*
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* Currently, this is only used with base 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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* Returns NULL if no suitable joins were found, else the last suitable
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* joinrel processed. (The only caller who checks the return value is
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* geqo_eval.c, and it sets things up so there can be no more than one
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* "suitable" joinrel; so we don't bother with returning a list.)
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*/
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RelOptInfo *
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make_rels_by_clauseless_joins(Query *root,
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RelOptInfo *old_rel,
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List *other_rels)
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{
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RelOptInfo *result = NULL;
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List *i;
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foreach(i, other_rels)
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{
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RelOptInfo *other_rel = (RelOptInfo *) lfirst(i);
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if (nonoverlap_setsi(other_rel->relids, old_rel->relids))
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result = make_join_rel(root, old_rel, other_rel);
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}
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return result;
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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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* The join rel is stored in the query's join_rel_list.
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*/
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static RelOptInfo *
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make_join_rel(Query *root, RelOptInfo *rel1, RelOptInfo *rel2)
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{
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RelOptInfo *joinrel;
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List *restrictlist;
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/*
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* Find or build the join RelOptInfo, and compute the restrictlist
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* that goes with this particular joining.
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*/
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joinrel = get_join_rel(root, rel1, rel2, &restrictlist);
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/*
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* We consider paths using each rel as both outer and inner.
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*/
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add_paths_to_joinrel(root, joinrel, rel1, rel2, restrictlist);
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add_paths_to_joinrel(root, joinrel, rel2, rel1, restrictlist);
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return joinrel;
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}
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