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Commitf01313b

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Improve create_unique_path to not be fooled by unrelated clauses that happen
to be syntactically part of a semijoin clause. For example givenWHERE EXISTS(SELECT ... WHERE upper.var = lower.var AND some-condition)where some-condition is just a restriction on the lower relation, we canuse unique-ification on lower.var after having applied some-condition withinthe scan on lower.
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‎src/backend/optimizer/util/pathnode.c

Lines changed: 60 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.149 2009/01/01 17:23:44 momjian Exp $
11+
* $PostgreSQL: pgsql/src/backend/optimizer/util/pathnode.c,v 1.150 2009/02/27 00:06:27 tgl Exp $
1212
*
1313
*-------------------------------------------------------------------------
1414
*/
@@ -765,19 +765,34 @@ create_unique_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
765765
*/
766766
oldcontext=MemoryContextSwitchTo(root->planner_cxt);
767767

768-
/*
768+
/*----------
769769
* Look to see whether the semijoin's join quals consist of AND'ed
770770
* equality operators, with (only) RHS variables on only one side of
771771
* each one. If so, we can figure out how to enforce uniqueness for
772772
* the RHS.
773773
*
774+
* Note that the input join_quals list is the list of quals that are
775+
* *syntactically* associated with the semijoin, which in practice means
776+
* the synthesized comparison list for an IN or the WHERE of an EXISTS.
777+
* Particularly in the latter case, it might contain clauses that aren't
778+
* *semantically* associated with the join, but refer to just one side or
779+
* the other. We can ignore such clauses here, as they will just drop
780+
* down to be processed within one side or the other. (It is okay to
781+
* consider only the syntactically-associated clauses here because for a
782+
* semijoin, no higher-level quals could refer to the RHS, and so there
783+
* can be no other quals that are semantically associated with this join.
784+
* We do things this way because it is useful to be able to run this test
785+
* before we have extracted the list of quals that are actually
786+
* semantically associated with the particular join.)
787+
*
774788
* Note that the in_operators list consists of the joinqual operators
775789
* themselves (but commuted if needed to put the RHS value on the right).
776790
* These could be cross-type operators, in which case the operator
777791
* actually needed for uniqueness is a related single-type operator.
778792
* We assume here that that operator will be available from the btree
779793
* or hash opclass when the time comes ... if not, create_unique_plan()
780794
* will fail.
795+
*----------
781796
*/
782797
in_operators=NIL;
783798
uniq_exprs=NIL;
@@ -791,19 +806,52 @@ create_unique_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
791806
Node*right_expr;
792807
Relidsleft_varnos;
793808
Relidsright_varnos;
809+
Relidsall_varnos;
794810

795-
/* must be binary opclause... */
796-
if (!IsA(op,OpExpr))
797-
gotono_unique_path;
798-
if (list_length(op->args)!=2)
811+
/* Is it a binary opclause? */
812+
if (!IsA(op,OpExpr)||
813+
list_length(op->args)!=2)
814+
{
815+
/* No, but does it reference both sides? */
816+
all_varnos=pull_varnos((Node*)op);
817+
if (!bms_overlap(all_varnos,sjinfo->syn_righthand)||
818+
bms_is_subset(all_varnos,sjinfo->syn_righthand))
819+
{
820+
/*
821+
* Clause refers to only one rel, so ignore it --- unless it
822+
* contains volatile functions, in which case we'd better
823+
* punt.
824+
*/
825+
if (contain_volatile_functions((Node*)op))
826+
gotono_unique_path;
827+
continue;
828+
}
829+
/* Non-operator clause referencing both sides, must punt */
799830
gotono_unique_path;
831+
}
832+
833+
/* Extract data from binary opclause */
800834
opno=op->opno;
801835
left_expr=linitial(op->args);
802836
right_expr=lsecond(op->args);
803-
804-
/* check rel membership of arguments */
805837
left_varnos=pull_varnos(left_expr);
806838
right_varnos=pull_varnos(right_expr);
839+
all_varnos=bms_union(left_varnos,right_varnos);
840+
841+
/* Does it reference both sides? */
842+
if (!bms_overlap(all_varnos,sjinfo->syn_righthand)||
843+
bms_is_subset(all_varnos,sjinfo->syn_righthand))
844+
{
845+
/*
846+
* Clause refers to only one rel, so ignore it --- unless it
847+
* contains volatile functions, in which case we'd better punt.
848+
*/
849+
if (contain_volatile_functions((Node*)op))
850+
gotono_unique_path;
851+
continue;
852+
}
853+
854+
/* check rel membership of arguments */
807855
if (!bms_is_empty(right_varnos)&&
808856
bms_is_subset(right_varnos,sjinfo->syn_righthand)&&
809857
!bms_overlap(left_varnos,sjinfo->syn_righthand))
@@ -845,6 +893,10 @@ create_unique_path(PlannerInfo *root, RelOptInfo *rel, Path *subpath,
845893
uniq_exprs=lappend(uniq_exprs,copyObject(right_expr));
846894
}
847895

896+
/* Punt if we didn't find at least one column to unique-ify */
897+
if (uniq_exprs==NIL)
898+
gotono_unique_path;
899+
848900
/*
849901
* The expressions we'd need to unique-ify mustn't be volatile.
850902
*/

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