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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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9
src/backend/access/transam/xlog.c
View File

@@ -134,6 +134,7 @@ int CommitSiblings = 5; /* # concurrent xacts needed to sleep */
int wal_retrieve_retry_interval = 5000;
int max_slot_wal_keep_size_mb = -1;
int wal_decode_buffer_size = 512 * 1024;
bool track_wal_io_timing = false;
#ifdef WAL_DEBUG
bool XLOG_DEBUG = false;
@@ -2437,7 +2438,7 @@ XLogWrite(XLogwrtRqst WriteRqst, TimeLineID tli, bool flexible)
/*
* Measure I/O timing to write WAL data, for pg_stat_io.
*/
start = pgstat_prepare_io_time();
start = pgstat_prepare_io_time(track_wal_io_timing);
pgstat_report_wait_start(WAIT_EVENT_WAL_WRITE);
written = pg_pwrite(openLogFile, from, nleft, startoffset);
@@ -3248,7 +3249,7 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
errmsg("could not create file \"%s\": %m", tmppath)));
/* Measure I/O timing when initializing segment */
io_start = pgstat_prepare_io_time();
io_start = pgstat_prepare_io_time(track_wal_io_timing);
pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_WRITE);
save_errno = 0;
@@ -3310,7 +3311,7 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
}
/* Measure I/O timing when flushing segment */
io_start = pgstat_prepare_io_time();
io_start = pgstat_prepare_io_time(track_wal_io_timing);
pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_SYNC);
if (pg_fsync(fd) != 0)
@@ -8744,7 +8745,7 @@ issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
/*
* Measure I/O timing to sync the WAL file for pg_stat_io.
*/
start = pgstat_prepare_io_time();
start = pgstat_prepare_io_time(track_wal_io_timing);
pgstat_report_wait_start(WAIT_EVENT_WAL_SYNC);
switch (wal_sync_method)