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Optimize check for pending backend IO stats

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This commit changes the backend stats code so as we rely on a single
boolean rather than a repeated check based on pg_memory_is_all_zeros()
in the code, making it cheaper should PgStat_PendingIO get bigger in
size.

The frequency of backend stats reports is not a bottleneck, but there is
no reason to not make that cheaper, and the logic is simple as the only
entry points updating backend IO stats are pgstat_count_backend_io_op()
and pgstat_count_backend_io_op_time().

Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Reviewed-by: Xuneng Zhou <xunengzhou@gmail.com>
Discussion: https://postgr.es/m/Z8WYf1jyy4MwOveQ@ip-10-97-1-34.eu-west-3.compute.internal
This commit is contained in:
Michael Paquier 2025-03-19 08:03:06 +09:00
parent 7fb418f020
commit 6d3ea48ff1
1 changed files with 11 additions and 8 deletions
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19
src/backend/utils/activity/pgstat_backend.c
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@ -37,6 +37,7 @@
* memory allocation.
*/
static PgStat_BackendPending PendingBackendStats;
static bool backend_has_iostats = false;
/*
* WAL usage counters saved from pgWalUsage at the previous call to
@ -63,6 +64,8 @@ pgstat_count_backend_io_op_time(IOObject io_object, IOContext io_context,
INSTR_TIME_ADD(PendingBackendStats.pending_io.pending_times[io_object][io_context][io_op],
io_time);
backend_has_iostats = true;
}
void
@ -76,6 +79,8 @@ pgstat_count_backend_io_op(IOObject io_object, IOContext io_context,
PendingBackendStats.pending_io.counts[io_object][io_context][io_op] += cnt;
PendingBackendStats.pending_io.bytes[io_object][io_context][io_op] += bytes;
backend_has_iostats = true;
}
/*
@ -158,8 +163,7 @@ pgstat_flush_backend_entry_io(PgStat_EntryRef *entry_ref)
* statistics. In this case, avoid unnecessarily modifying the stats
* entry.
*/
if (pg_memory_is_all_zeros(&PendingBackendStats.pending_io,
sizeof(struct PgStat_PendingIO)))
if (!backend_has_iostats)
return;
shbackendent = (PgStatShared_Backend *) entry_ref->shared_stats;
@ -190,6 +194,8 @@ pgstat_flush_backend_entry_io(PgStat_EntryRef *entry_ref)
* Clear out the statistics buffer, so it can be re-used.
*/
MemSet(&PendingBackendStats.pending_io, 0, sizeof(PgStat_PendingIO));
backend_has_iostats = false;
}
/*
@ -259,9 +265,7 @@ pgstat_flush_backend(bool nowait, bits32 flags)
return false;
/* Some IO data pending? */
if ((flags & PGSTAT_BACKEND_FLUSH_IO) &&
!pg_memory_is_all_zeros(&PendingBackendStats.pending_io,
sizeof(struct PgStat_PendingIO)))
if ((flags & PGSTAT_BACKEND_FLUSH_IO) && backend_has_iostats)
has_pending_data = true;
/* Some WAL data pending? */
@ -298,9 +302,7 @@ pgstat_backend_have_pending_cb(void)
if (!pgstat_tracks_backend_bktype(MyBackendType))
return false;
return (!pg_memory_is_all_zeros(&PendingBackendStats,
sizeof(struct PgStat_BackendPending)) ||
pgstat_backend_wal_have_pending());
return (backend_has_iostats || pgstat_backend_wal_have_pending());
}
/*
@ -335,6 +337,7 @@ pgstat_create_backend(ProcNumber procnum)
pgstat_unlock_entry(entry_ref);
MemSet(&PendingBackendStats, 0, sizeof(PgStat_BackendPending));
backend_has_iostats = false;
/*
* Initialize prevBackendWalUsage with pgWalUsage so that