From b7f166efade004ba293f52b672961ae064d202cd Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Tue, 6 Oct 2020 11:43:53 -0400 Subject: [PATCH] Build EC members for child join rels in the right memory context. This patch prevents crashes or wrong plans when partition-wise joins are considered during GEQO planning, as a consequence of the EquivalenceClass data structures becoming corrupt after a GEQO context reset. A remaining problem is that successive GEQO cycles will make multiple copies of the required EC members, since add_child_join_rel_equivalences has no idea that such members might exist already. For now we'll just live with that. The lack of field complaints of crashes suggests that this is a mighty little-used situation. Back-patch to v12 where this code was introduced. Discussion: https://postgr.es/m/1683100.1601860653@sss.pgh.pa.us --- src/backend/optimizer/path/equivclass.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c index d3d826b790e..823422edad0 100644 --- a/src/backend/optimizer/path/equivclass.c +++ b/src/backend/optimizer/path/equivclass.c @@ -2380,6 +2380,7 @@ add_child_join_rel_equivalences(PlannerInfo *root, Relids top_parent_relids = child_joinrel->top_parent_relids; Relids child_relids = child_joinrel->relids; Bitmapset *matching_ecs; + MemoryContext oldcontext; int i; Assert(IS_JOIN_REL(child_joinrel) && IS_JOIN_REL(parent_joinrel)); @@ -2387,6 +2388,16 @@ add_child_join_rel_equivalences(PlannerInfo *root, /* We need consider only ECs that mention the parent joinrel */ matching_ecs = get_eclass_indexes_for_relids(root, top_parent_relids); + /* + * If we're being called during GEQO join planning, we still have to + * create any new EC members in the main planner context, to avoid having + * a corrupt EC data structure after the GEQO context is reset. This is + * problematic since we'll leak memory across repeated GEQO cycles. For + * now, though, bloat is better than crash. If it becomes a real issue + * we'll have to do something to avoid generating duplicate EC members. + */ + oldcontext = MemoryContextSwitchTo(root->planner_cxt); + i = -1; while ((i = bms_next_member(matching_ecs, i)) >= 0) { @@ -2486,6 +2497,8 @@ add_child_join_rel_equivalences(PlannerInfo *root, } } } + + MemoryContextSwitchTo(oldcontext); }