Speed up match_eclasses_to_foreign_key_col() when there are many ECs.

tglsfdc · tglsfdc · commit fa86238f1eac · 2019-02-20T20:53:17.000-05:00
Check ec_relids before bothering to iterate through the EC members. On a perhaps extreme, but still real-world, query in which match_eclasses_to_foreign_key_col() accounts for the bulk of the planner's runtime, this saves nearly 40% of the runtime. It's a bit of a stopgap fix, but it's simple enough to be back-patched to 9.6 where this code came in; so let's do that. David Rowley Discussion: https://postgr.es/m/6970.1545327857@sss.pgh.pa.us
diff --git a/src/backend/optimizer/path/equivclass.c b/src/backend/optimizer/path/equivclass.c
@@ -2052,6 +2052,14 @@ match_eclasses_to_foreign_key_col(PlannerInfo *root,
 			continue;
 		/* Note: it seems okay to match to "broken" eclasses here */
 
+		/*
+		 * If eclass visibly doesn't have members for both rels, there's no
+		 * need to grovel through the members.
+		 */
+		if (!bms_is_member(var1varno, ec->ec_relids) ||
+			!bms_is_member(var2varno, ec->ec_relids))
+			continue;
+
 		foreach(lc2, ec->ec_members)
 		{
 			EquivalenceMember *em = (EquivalenceMember *) lfirst(lc2);
