Hello Tom,
10.02.2026 19:06, Tom Lane wrote:
Several BF animals have intermittently shown this regression diff:
diff -U3
/home/bf/bf-build/culicidae/HEAD/pgsql/contrib/postgres_fdw/expected/postgres_fdw.out
/home/bf/bf-build/culicidae/HEAD/pgsql.build/testrun/postgres_fdw-running/regress/results/postgres_fdw.out
---
/home/bf/bf-build/culicidae/HEAD/pgsql/contrib/postgres_fdw/expected/postgres_fdw.out
2025-12-29 19:48:22.661603936 +0100
+++
/home/bf/bf-build/culicidae/HEAD/pgsql.build/testrun/postgres_fdw-running/regress/results/postgres_fdw.out
2026-02-10 00:31:31.856460156 +0100
@@ -6519,6 +6519,7 @@
UPDATE ft2 SET c3 = 'bar' WHERE postgres_fdw_abs(c1) > 2000 RETURNING *;
c1 | c2 | c3 | c4 | c5 | c6 | c7 | c8
------+----+-----+----+----+----+------------+----
+ 2010 | 0 | bar | | | | ft2 |
2001 | 1 | bar | | | | ft2 |
2002 | 2 | bar | | | | ft2 |
2003 | 3 | bar | | | | ft2 |
@@ -6528,7 +6529,6 @@
2007 | 7 | bar | | | | ft2 |
2008 | 8 | bar | | | | ft2 |
2009 | 9 | bar | | | | ft2 |
- 2010 | 0 | bar | | | | ft2 |
(10 rows)
EXPLAIN (verbose, costs off)
The above is from culicidae [1], and greenfly has shown it a few times
[2], and here's one from scorpion [3], and crake on a back branch [4],
and there are a few more in the past 90 days.
FWIW, all the failures of this ilk are tracked at [1].
It's pretty clear what is happening: the rows we are looking at are
being returned by a seqscan, and they were just inserted a few lines
above into a table that has been modified multiple times already.
So the test is reliant on them being inserted in sequence at the
end of the table, yet sometimes the last row is going into free
space someplace earlier.
One's first instinct is to blame autovacuum, but the test already
goes out of its way to disable that:
-- Disable autovacuum for these tables to avoid unexpected effects of that
ALTER TABLE "S 1"."T 1" SET (autovacuum_enabled = 'false');
I reproduced and reported the failure before, please look at [2] —
probably some information there could be helpful...
[1]
https://wiki.postgresql.org/wiki/Known_Buildfarm_Test_Failures#postgres_fdw.sql_might_fail_due_to_autovacuum
[2]
https://www.postgresql.org/message-id/flat/867266ef-3dd1-44a9-a203-27cb5d2be58d%40gmail.com
Best regards,
Alexander
