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Speed up match_eclasses_to_foreign_key_col() when there are many ECs.

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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
This commit is contained in:
Tom Lane 2019-02-20 20:53:08 -05:00
parent d26a810ebf
commit fa86238f1e
1 changed files with 8 additions and 0 deletions
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8
src/backend/optimizer/path/equivclass.c
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@ -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);