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Build EC members for child join rels in the right memory context.

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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
This commit is contained in:
Tom Lane 2020-10-06 11:43:54 -04:00
parent 9b8e6857b8
commit 3d69efc4f0
1 changed files with 13 additions and 0 deletions
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13
src/backend/optimizer/path/equivclass.c
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@ -2234,10 +2234,21 @@ add_child_join_rel_equivalences(PlannerInfo *root,
{
Relids top_parent_relids = child_joinrel->top_parent_relids;
Relids child_relids = child_joinrel->relids;
MemoryContext oldcontext;
ListCell *lc1;
Assert(IS_JOIN_REL(child_joinrel) && IS_JOIN_REL(parent_joinrel));
/*
* 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);
foreach(lc1, root->eq_classes)
{
EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc1);
@ -2334,6 +2345,8 @@ add_child_join_rel_equivalences(PlannerInfo *root,
}
}
}
MemoryContextSwitchTo(oldcontext);
}