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Fix waiting in RegisterSyncRequest().

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If we run out of space in the checkpointer sync request queue (which is
hopefully rare on real systems, but common with very small buffer pool),
we wait for it to drain.  While waiting, we should report that as a wait
event so that users know what is going on, and also handle postmaster
death, since otherwise the loop might never terminate if the
checkpointer has exited.

Back-patch to 12.  Although the problem exists in earlier releases too,
the code is structured differently before 12 so I haven't gone any
further for now, in the absence of field complaints.

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 15:35:42 +13:00
parent b61e6214cf
commit 1396b5c6ed
4 changed files with 13 additions and 2 deletions
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5
doc/src/sgml/monitoring.sgml
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@ -2242,6 +2242,11 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
<entry>Waiting during recovery when WAL data is not available from any
source (<filename>pg_wal</filename>, archive or stream).</entry>
</row>
<row>
<entry><literal>RegisterSyncRequest</literal></entry>
<entry>Waiting while sending synchronization requests to the
checkpointer, because the request queue is full.</entry>
</row>
<row>
<entry><literal>VacuumDelay</literal></entry>
<entry>Waiting in a cost-based vacuum delay point.</entry>