From 5843659d091bfb6f2c60e010ea1fd00e55ee6ada Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sun, 20 Jun 2021 11:48:44 -0400
Subject: Stabilize test case added by commit f61db909d.

Buildfarm members ayu and tern have sometimes shown a different
plan than expected for this query.  I'd been unable to reproduce
that before today, but I finally realized what is happening.
If there is a concurrent open transaction (probably an autovacuum
run in the buildfarm, but this can also be arranged manually),
then the index entries for the rows removed by the DELETE a few
lines up are not killed promptly, causing a change in the planner's
estimate of the extremal value of ft2.c1, which moves the rowcount
estimate for "c1 > 1100" by enough to change the join plan from
nestloop to hash.

To fix, change the query condition to "c1 > 1000", causing the
hash plan to be preferred whether or not a concurrent open
transaction exists.  Since this UPDATE is tailored to be a no-op,
nothing else changes.

Report: https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=ayu&dt=2021-06-09%2022%3A45%3A48
Report: https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=ayu&dt=2021-06-13%2022%3A38%3A18
Report: https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=tern&dt=2021-06-20%2004%3A55%3A36
---
 contrib/postgres_fdw/sql/postgres_fdw.sql | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

(limited to 'contrib/postgres_fdw/sql/postgres_fdw.sql')

diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 34a67d71605..8983209c74b 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -1259,9 +1259,9 @@ UPDATE ft2 AS target SET (c2) = (
 -- but a SET clause that can't be
 EXPLAIN (VERBOSE, COSTS OFF)
 UPDATE ft2 d SET c2 = CASE WHEN random() >= 0 THEN d.c2 ELSE 0 END
-  FROM ft2 AS t WHERE d.c1 = t.c1 AND d.c1 > 1100;
+  FROM ft2 AS t WHERE d.c1 = t.c1 AND d.c1 > 1000;
 UPDATE ft2 d SET c2 = CASE WHEN random() >= 0 THEN d.c2 ELSE 0 END
-  FROM ft2 AS t WHERE d.c1 = t.c1 AND d.c1 > 1100;
+  FROM ft2 AS t WHERE d.c1 = t.c1 AND d.c1 > 1000;
 
 -- Test UPDATE/DELETE with WHERE or JOIN/ON conditions containing
 -- user-defined operators/functions
-- 
cgit v1.2.3

