Recent "could not register background process" buildfarm failures
In the past three weeks, two different buildfarm animals have
reported failures like this in test_shm_mq [1]https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=tayra&dt=2026-07-25%2005%3A43%3A54[2]https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=akepa&dt=2026-08-17%2021%3A37%3A41[3]https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=akepa&dt=2026-08-18%2013%3A52%3A05:
# SELECT test_shm_mq(1024, 'a', 2001, 1);
# - test_shm_mq
# --------------
# -
# -(1 row)
# -
# +ERROR: could not register background process
# +HINT: You may need to increase "max_worker_processes".
test_shm_mq itself hasn't changed meaningfully in ages,
so it seems like some recent change somewhere else has increased
the probability of not being able to get a worker process.
Maybe autovacuum is eating too many workers? Any thoughts?
regards, tom lane
[1]: https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=tayra&dt=2026-07-25%2005%3A43%3A54
[2]: https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=akepa&dt=2026-08-17%2021%3A37%3A41
[3]: https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=akepa&dt=2026-08-18%2013%3A52%3A05
On 2026-Aug-18, Tom Lane wrote:
# +ERROR: could not register background process
# +HINT: You may need to increase "max_worker_processes".test_shm_mq itself hasn't changed meaningfully in ages,
so it seems like some recent change somewhere else has increased
the probability of not being able to get a worker process.
Maybe autovacuum is eating too many workers? Any thoughts?
Hm, autovacuum does not use workers from the bgworker pool AFAIK.
Repack concurrently does. However, I don't think we use repack
concurrently anywhere in the standard tests; we only run it in the
test_decoding and injection_point tests, which have separate instances.
--
Álvaro Herrera Breisgau, Deutschland — https://www.EnterpriseDB.com/
"La persona que no quería pecar / estaba obligada a sentarse
en duras y empinadas sillas / desprovistas, por cierto
de blandos atenuantes" (Patricio Vogel)
On 18 Aug 2026, at 19:44, Álvaro Herrera <alvherre@kurilemu.de> wrote:
On 2026-Aug-18, Tom Lane wrote:
# +ERROR: could not register background process
# +HINT: You may need to increase "max_worker_processes".test_shm_mq itself hasn't changed meaningfully in ages,
so it seems like some recent change somewhere else has increased
the probability of not being able to get a worker process.
Maybe autovacuum is eating too many workers? Any thoughts?Hm, autovacuum does not use workers from the bgworker pool AFAIK.
Repack concurrently does. However, I don't think we use repack
concurrently anywhere in the standard tests; we only run it in the
test_decoding and injection_point tests, which have separate instances.
Online checksums also use bgworkers but it too should not be running here, and
looking at it I didn't see evidence of it interfering. I'll have another look
in the morning with fresh eyes.
--
Daniel Gustafsson