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Commit53c6daf

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Fix two latent(?) bugs in equivclass.c.
get_eclass_for_sort_expr() computes expr_relids and nullable_relidsearly on, even though they won't be needed unless we make a newEquivalenceClass, which we often don't. Aside from the probably-minorinefficiency, there's a memory management problem: these bitmapsets willbe built in the caller's context, leading to dangling pointers if thatis shorter-lived than root->planner_cxt. This would be a live bug ifget_eclass_for_sort_expr() could be called with create_it = true duringGEQO join planning. So far as I can find, the core code never doesthat, but it's hard to be sure that no extensions do, especially sincethe comments make it clear that that's supposed to be a supported case.Fix by not computing these values until we've switched into planner_cxtto build the new EquivalenceClass.generate_join_implied_equalities() uses inner_rel->relids to look uprelevant eclasses, but it ought to be using nominal_inner_relids.This is presently harmless because a child RelOptInfo will always haveexactly the same eclass_indexes as its topmost parent; but that mightnot be true forever, and anyway it makes the code confusing.The first of these is old (introduced by me inf3b3b8d), so back-patchto all supported branches. The second only dates to v13, but we mightas well back-patch it to keep the code looking similar across branches.Discussion:https://postgr.es/m/1508010.1601832581@sss.pgh.pa.us
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‎src/backend/optimizer/path/equivclass.c

Lines changed: 8 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -634,12 +634,6 @@ get_eclass_for_sort_expr(PlannerInfo *root,
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*/
635635
expr=canonicalize_ec_expression(expr,opcintype,collation);
636636

637-
/*
638-
* Get the precise set of nullable relids appearing in the expression.
639-
*/
640-
expr_relids=pull_varnos((Node*)expr);
641-
nullable_relids=bms_intersect(nullable_relids,expr_relids);
642-
643637
/*
644638
* Scan through the existing EquivalenceClasses for a match
645639
*/
@@ -716,6 +710,12 @@ get_eclass_for_sort_expr(PlannerInfo *root,
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if (newec->ec_has_volatile&&sortref==0)/* should not happen */
717711
elog(ERROR,"volatile EquivalenceClass has no sortref");
718712

713+
/*
714+
* Get the precise set of nullable relids appearing in the expression.
715+
*/
716+
expr_relids=pull_varnos((Node*)expr);
717+
nullable_relids=bms_intersect(nullable_relids,expr_relids);
718+
719719
newem=add_eq_member(newec,copyObject(expr),expr_relids,
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nullable_relids, false,opcintype);
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@@ -1171,9 +1171,9 @@ generate_join_implied_equalities(PlannerInfo *root,
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}
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/*
1174-
* Get all eclassesin common between inner_rel's relidsandouter_relids
1174+
* Get all eclassesthat mention both innerandouter sides of the join
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*/
1176-
matching_ecs=get_common_eclass_indexes(root,inner_rel->relids,
1176+
matching_ecs=get_common_eclass_indexes(root,nominal_inner_relids,
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outer_relids);
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i=-1;

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