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Re-add GUC track_wal_io_timing

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This commit is a rework of 2421e9a51d, about which Andres Freund has
raised some concerns as it is valuable to have both track_io_timing and
track_wal_io_timing in some cases, as the WAL write and fsync paths can
be a major bottleneck for some workloads.  Hence, it can be relevant to
not calculate the WAL timings in environments where pg_test_timing
performs poorly while capturing some IO data under track_io_timing for
the non-WAL IO paths.  The opposite can be also true: it should be
possible to disable the non-WAL timings and enable the WAL timings (the
previous GUC setups allowed this possibility).

track_wal_io_timing is added back in this commit, controlling if WAL
timings should be calculated in pg_stat_io for the read, fsync and write
paths, as done previously with pg_stat_wal.  pg_stat_wal previously
tracked only the sync and write parts (now removed), read stats is new
data tracked in pg_stat_io, all three are aggregated if
track_wal_io_timing is enabled.  The read part matters during recovery
or if a XLogReader is used.

Extra note: more control over if the types of timings calculated in
pg_stat_io could be done with a GUC that lists pairs of (IOObject,IOOp).

Reported-by: Andres Freund <andres@anarazel.de>
Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Co-authored-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/3opf2wh2oljco6ldyqf7ukabw3jijnnhno6fjb4mlu6civ5h24@fcwmhsgmlmzu
This commit is contained in:
Michael Paquier
2025-02-26 09:49:59 +09:00
parent a5cbdeb98a
commit 6c349d83b6
15 changed files with 96 additions and 32 deletions
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31
doc/src/sgml/monitoring.sgml
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@@ -183,6 +183,11 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
of block read, write, extend, and fsync times.
</para>
<para>
The parameter <xref linkend="guc-track-wal-io-timing"/> enables monitoring
of WAL read, write and fsync times.
</para>
<para>
Normally these parameters are set in <filename>postgresql.conf</filename> so
that they apply to all server processes, but it is possible to turn
@@ -2723,7 +2728,11 @@ description | Waiting for a newly initialized WAL file to reach durable storage
</para>
<para>
Time spent in read operations in milliseconds (if
<xref linkend="guc-track-io-timing"/> is enabled, otherwise zero)
<xref linkend="guc-track-io-timing"/> is enabled and
<varname>object</varname> is not <literal>wal</literal>,
or if <xref linkend="guc-track-wal-io-timing"/> is enabled
and <varname>object</varname> is <literal>wal</literal>,
otherwise zero)
</para>
</entry>
</row>
@@ -2757,7 +2766,11 @@ description | Waiting for a newly initialized WAL file to reach durable storage
</para>
<para>
Time spent in write operations in milliseconds (if
<xref linkend="guc-track-io-timing"/> is enabled, otherwise zero)
<xref linkend="guc-track-io-timing"/> is enabled and
<varname>object</varname> is not <literal>wal</literal>,
or if <xref linkend="guc-track-wal-io-timing"/> is enabled
and <varname>object</varname> is <literal>wal</literal>,
otherwise zero)
</para>
</entry>
</row>
@@ -2816,8 +2829,12 @@ description | Waiting for a newly initialized WAL file to reach durable storage
<structfield>extend_time</structfield> <type>double precision</type>
</para>
<para>
Time spent in extend operations in milliseconds (if
<xref linkend="guc-track-io-timing"/> is enabled, otherwise zero)
Time spent in extend operations in milliseconds. (if
<xref linkend="guc-track-io-timing"/> is enabled and
<varname>object</varname> is not <literal>wal</literal>,
or if <xref linkend="guc-track-wal-io-timing"/> is enabled
and <varname>object</varname> is <literal>wal</literal>,
otherwise zero)
</para>
</entry>
</row>
@@ -2887,7 +2904,11 @@ description | Waiting for a newly initialized WAL file to reach durable storage
</para>
<para>
Time spent in fsync operations in milliseconds (if
<xref linkend="guc-track-io-timing"/> is enabled, otherwise zero)
<xref linkend="guc-track-io-timing"/> is enabled and
<varname>object</varname> is not <literal>wal</literal>,
or if <xref linkend="guc-track-wal-io-timing"/> is enabled
and <varname>object</varname> is <literal>wal</literal>,
otherwise zero)
</para>
</entry>
</row>