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Commit1f03630

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Adjust join_search_one_level's handling of clauseless joins.
For an initial relation that lacks any join clauses (that is, it has to becartesian-product-joined to the rest of the query), we considered onlycartesian joins with initial rels appearing later in the initial-relationslist. This creates an undesirable dependency on FROM-list order. We wouldnever fail to find a plan, but perhaps we might not find the best availableplan. Noted while discussing the logic with Amit Kapila.Improve the comments a bit in this area, too.Arguably this is a bug fix, but given the lack of complaints from thefield I'll refrain from back-patching.
1 parent5b7b551 commit1f03630

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‎src/backend/optimizer/path/joinrels.c

Lines changed: 27 additions & 19 deletions
Original file line numberDiff line numberDiff line change
@@ -65,33 +65,34 @@ join_search_one_level(PlannerInfo *root, int level)
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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
71-
* 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
73-
* 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);
78-
ListCell*other_rels;
79-
80-
if (level==2)
81-
other_rels=lnext(r);/* only consider remaining initial
82-
* rels */
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else
84-
other_rels=list_head(joinrels[1]);/* consider all initial
85-
* rels */
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8773
if (old_rel->joininfo!=NIL||old_rel->has_eclass_joins||
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has_join_restriction(root,old_rel))
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{
9076
/*
91-
* There are relevant join clauses or join order restrictions,
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* so consider joins between this rel and (only) those rels it is
93-
* linked to by a clause or restriction.
77+
* There are join clauses or join order restrictions relevant to
78+
* this rel, so consider joins between this rel and (only) those
79+
* initial rels it is linked to by a clause or restriction.
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*
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* At level 2 this condition is symmetric, so there is no need to
82+
* look at initial rels before this one in the list; we already
83+
* considered such joins when we were at the earlier rel. (The
84+
* mirror-image joins are handled automatically by make_join_rel.)
85+
* In later passes (level > 2), we join rels of the previous level
86+
* to each initial rel they don't already include but have a join
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* clause or restriction with.
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*/
89+
ListCell*other_rels;
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91+
if (level==2)/* consider remaining initial rels */
92+
other_rels=lnext(r);
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else/* consider all initial rels */
94+
other_rels=list_head(joinrels[1]);
95+
9596
make_rels_by_clause_joins(root,
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old_rel,
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other_rels);
@@ -102,10 +103,17 @@ join_search_one_level(PlannerInfo *root, int level)
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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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* We consider a cartesian product with each not-already-included
108+
* initial rel, whether it has other join clauses or not. At
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* level 2, if there are two or more clauseless initial rels, we
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* will redundantly consider joining them in both directions; but
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* such cases aren't common enough to justify adding complexity to
112+
* avoid the duplicated effort.
105113
*/
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make_rels_by_clauseless_joins(root,
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old_rel,
108-
other_rels);
116+
list_head(joinrels[1]));
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}
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}
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@@ -135,7 +143,7 @@ join_search_one_level(PlannerInfo *root, int level)
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ListCell*r2;
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/*
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* We can ignoreclauseless joinshere,*except* when they
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* We can ignorerelations without join clauseshere,unless they
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* participate in join-order restrictions --- then we might have
140148
* to force a bushy join plan.
141149
*/

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