database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-09-02 04:21:28 +03:00
Code Activity

Re-add GUC track_wal_io_timing

Browse Source 
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
Download Patch File Download Diff File Expand all files Collapse all files

4
doc/src/sgml/wal.sgml
View File

@@ -808,7 +808,7 @@
<para>
There are two internal functions to write WAL data to disk:
<function>XLogWrite</function> and <function>issue_xlog_fsync</function>.
When <xref linkend="guc-track-io-timing"/> is enabled, the total
When <xref linkend="guc-track-wal-io-timing"/> is enabled, the total
amounts of time <function>XLogWrite</function> writes and
<function>issue_xlog_fsync</function> syncs WAL data to disk are counted as
<varname>write_time</varname> and <varname>fsync_time</varname> in
@@ -828,7 +828,7 @@
<literal>fsync</literal>, or <literal>fsync_writethrough</literal>,
the write operation moves WAL buffers to kernel cache and
<function>issue_xlog_fsync</function> syncs them to disk. Regardless
of the setting of <varname>track_io_timing</varname>, the number
of the setting of <varname>track_wal_io_timing</varname>, the number
of times <function>XLogWrite</function> writes and
<function>issue_xlog_fsync</function> syncs WAL data to disk are also
counted as <varname>writes</varname> and <varname>fsyncs</varname>