pgsql: Stabilize 019_replslot_limit

Stabilize 019_replslot_limit

The test assumed that advancing WAL would lead to a checkpoint that
invalidates the obsolete replication slot. If a checkpoint that started
before the WAL switch completes first, the following checkpoint can be
skipped as idle, so the expected walsender termination is not logged.

Force a CHECKPOINT in a background psql session after advancing WAL, so
the slot invalidation is exercised deterministically.

This has been observed on buildfarm members alligator and partridge:
https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=alligator&dt=2024-12-13%2001%3A24%3A58
https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=partridge&dt=2026-08-06%2018%3A00%3A11

Backpatch to all supported versions.

Reported-by: Alexander Lakhin <exclusion(at)gmail(dot)com>
Author: Hayato Kuroda <kuroda(dot)hayato(at)fujitsu(dot)com>
Reviewed-by: Alexander Lakhin <exclusion(at)gmail(dot)com>
Reviewed-by: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Discussion: https://postgr.es/m/0b07ead5-a5da-445e-9698-a7d340708bdf@gmail.com
Backpatch-through: 14

Branch
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REL_18_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/5bf208645b1f989f2b643155d5313f9366b479d1

Modified Files
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src/test/recovery/t/019_replslot_limit.pl | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)