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Wake up for latches in CheckpointWriteDelay().

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The checkpointer shouldn't ignore its latch.  Other backends may be
waiting for it to drain the request queue.  Hopefully real systems don't
have a full queue often, but the condition is reached easily when
shared_buffers is small.

This involves defining a new wait event, which will appear in the
pg_stat_activity view often due to spread checkpoints.

Back-patch only to 14.  Even though the problem exists in earlier
branches too, it's hard to hit there.  In 14 we stopped using signal
handlers for latches on Linux, *BSD and macOS, which were previously
hiding this problem by interrupting the sleep (though not reliably, as
the signal could arrive before the sleep begins; precisely the problem
latches address).

Reported-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/20220226213942.nb7uvb2pamyu26dj%40alap3.anarazel.de
This commit is contained in:
Thomas Munro
2022-03-16 13:37:58 +13:00
parent a56e7b6601
commit 5e6368b42e
4 changed files with 15 additions and 1 deletions
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doc/src/sgml/monitoring.sgml
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@ -2235,6 +2235,10 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry><literal>BaseBackupThrottle</literal></entry>
<entry>Waiting during base backup when throttling activity.</entry>
</row>
<row>
<entry><literal>CheckpointerWriteDelay</literal></entry>
<entry>Waiting between writes while performing a checkpoint.</entry>
</row>
<row>
<entry><literal>PgSleep</literal></entry>
<entry>Waiting due to a call to <function>pg_sleep</function> or