From 1f94d76856bc7e473e300134e092eb231cba83fe Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Mon, 5 Oct 2020 13:15:39 -0400 Subject: [PATCH] Fix two latent(?) bugs in equivclass.c. get_eclass_for_sort_expr() computes expr_relids and nullable_relids early on, even though they won't be needed unless we make a new EquivalenceClass, which we often don't. Aside from the probably-minor inefficiency, there's a memory management problem: these bitmapsets will be built in the caller's context, leading to dangling pointers if that is shorter-lived than root->planner_cxt. This would be a live bug if get_eclass_for_sort_expr() could be called with create_it = true during GEQO join planning. So far as I can find, the core code never does that, but it's hard to be sure that no extensions do, especially since the 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_cxt to build the new EquivalenceClass. generate_join_implied_equalities() uses inner_rel->relids to look up relevant eclasses, but it ought to be using nominal_inner_relids. This is presently harmless because a child RelOptInfo will always have exactly the same eclass_indexes as its topmost parent; but that might not be true forever, and anyway it makes the code confusing. The first of these is old (introduced by me in f3b3b8d5b), so back-patch to all supported branches. The second only dates to v13, but we might as well back-patch it to keep the code looking similar across branches. Discussion: https://postgr.es/m/1508010.1601832581@sss.pgh.pa.us --- src/backend/optimizer/path/equivclass.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c index 85a0105e0e..e50a5d44af 100644 --- a/src/backend/optimizer/path/equivclass.c +++ b/src/backend/optimizer/path/equivclass.c @@ -629,12 +629,6 @@ get_eclass_for_sort_expr(PlannerInfo *root, */ expr = canonicalize_ec_expression(expr, opcintype, collation); - /* - * Get the precise set of nullable relids appearing in the expression. - */ - expr_relids = pull_varnos((Node *) expr); - nullable_relids = bms_intersect(nullable_relids, expr_relids); - /* * Scan through the existing EquivalenceClasses for a match */ @@ -711,6 +705,12 @@ get_eclass_for_sort_expr(PlannerInfo *root, if (newec->ec_has_volatile && sortref == 0) /* should not happen */ elog(ERROR, "volatile EquivalenceClass has no sortref"); + /* + * Get the precise set of nullable relids appearing in the expression. + */ + expr_relids = pull_varnos((Node *) expr); + nullable_relids = bms_intersect(nullable_relids, expr_relids); + newem = add_eq_member(newec, copyObject(expr), expr_relids, nullable_relids, false, opcintype);