Re-add GUC track_wal_io_timing

This commit is a rework of 2421e9a51d20, 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 <[email protected]>
Author: Bertrand Drouvot <[email protected]>
Co-authored-by: Michael Paquier <[email protected]>
Discussion: https://postgr.es/m/3opf2wh2oljco6ldyqf7ukabw3jijnnhno6fjb4mlu6civ5h24@fcwmhsgmlmzu

2 files changed, 2 insertions, 1 deletions

diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index 0a50d160bba..d313099c027 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -54,6 +54,7 @@ extern PGDLLIMPORT char *wal_consistency_checking_string;
 extern PGDLLIMPORT bool log_checkpoints;
 extern PGDLLIMPORT int CommitDelay;
 extern PGDLLIMPORT int CommitSiblings;
+extern PGDLLIMPORT bool track_wal_io_timing;
 extern PGDLLIMPORT int wal_decode_buffer_size;
 
 extern PGDLLIMPORT int CheckPointSegments;
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index fc651d03cf9..e64c527265b 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -564,7 +564,7 @@ extern bool pgstat_bktype_io_stats_valid(PgStat_BktypeIO *backend_io,
 										 BackendType bktype);
 extern void pgstat_count_io_op(IOObject io_object, IOContext io_context,
 							   IOOp io_op, uint32 cnt, uint64 bytes);
-extern instr_time pgstat_prepare_io_time(void);
+extern instr_time pgstat_prepare_io_time(bool track_io_guc);
 extern void pgstat_count_io_op_time(IOObject io_object, IOContext io_context,
 									IOOp io_op, instr_time start_time,
 									uint32 cnt, uint64 bytes);