postgres.git / summary / log / commit / refs

commit    3d69efc4f07d773329dfbd39d6ec67a025cf7339
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Tue Oct 06 15:43:54 2020 +0000
First released in: 14.0, 12.5, 13.1

    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 e50a5d44afc..b62b954e880 100644
--- a/src/backend/optimizer/path/equivclass.c
+++ b/src/backend/optimizer/path/equivclass.c
@@ -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);
 }
 
 


[parent: 9b8e6857b817]