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Move wal_buffers_full from PgStat_PendingWalStats to WalUsage

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wal_buffers_full has been introduced in pg_stat_wal in 8d9a935965f, as
some information providing metrics for the tuning of the GUC
wal_buffers.  WalUsage has been introduced before that in df3b181499.

Moving this field is proving to be beneficial for several reasons:
- This information can now be made available in more layers, providing
more granularity than just pg_stat_wal, on a per-query basis: EXPLAIN,
pgss and VACUUM/ANALYZE logs.
- A patch is under discussion to provide statistics for WAL at backend
level, and this move simplifies a bit the handling of pending
statistics.  The remaining data in PgStat_PendingWalStats now relates to
write/sync counters and times, with equivalents present in pg_stat_io,
that backend statistics are able to already track.  So this should cut
all the dependencies between PgStat_PendingWalStats and WAL stats at
backend level.

As of this change, wal_buffers_full only shows in pg_stat_wal.

Author: Bertrand Drouvot
Reviewed-by: Ilia Evdokimov
Discussion: https://postgr.es/m/Z6SOha5YFFgvpwQY@ip-10-97-1-34.eu-west-3.compute.internal
This commit is contained in:
Michael Paquier 2025-02-17 13:14:28 +09:00
parent 6a2275b895
commit eaf502747b
5 changed files with 5 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
src/backend/access/transam/xlog.c
View File

@ -2093,7 +2093,7 @@ AdvanceXLInsertBuffer(XLogRecPtr upto, TimeLineID tli, bool opportunistic)
WriteRqst.Flush = 0;
XLogWrite(WriteRqst, tli, false);
LWLockRelease(WALWriteLock);
PendingWalStats.wal_buffers_full++;
pgWalUsage.wal_buffers_full++;
TRACE_POSTGRESQL_WAL_BUFFER_WRITE_DIRTY_DONE();
}
}

2
src/backend/executor/instrument.c
View File

@ -280,6 +280,7 @@ WalUsageAdd(WalUsage *dst, WalUsage *add)
dst->wal_bytes += add->wal_bytes;
dst->wal_records += add->wal_records;
dst->wal_fpi += add->wal_fpi;
dst->wal_buffers_full += add->wal_buffers_full;
}
void
@ -288,4 +289,5 @@ WalUsageAccumDiff(WalUsage *dst, const WalUsage *add, const WalUsage *sub)
dst->wal_bytes += add->wal_bytes - sub->wal_bytes;
dst->wal_records += add->wal_records - sub->wal_records;
dst->wal_fpi += add->wal_fpi - sub->wal_fpi;
dst->wal_buffers_full += add->wal_buffers_full - sub->wal_buffers_full;
}

2
src/backend/utils/activity/pgstat_wal.c
View File

@ -123,7 +123,7 @@ pgstat_wal_flush_cb(bool nowait)
WALSTAT_ACC(wal_records, wal_usage_diff);
WALSTAT_ACC(wal_fpi, wal_usage_diff);
WALSTAT_ACC(wal_bytes, wal_usage_diff);
WALSTAT_ACC(wal_buffers_full, PendingWalStats);
WALSTAT_ACC(wal_buffers_full, wal_usage_diff);
WALSTAT_ACC(wal_write, PendingWalStats);
WALSTAT_ACC(wal_sync, PendingWalStats);
WALSTAT_ACC_INSTR_TIME(wal_write_time);

1
src/include/executor/instrument.h
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@ -53,6 +53,7 @@ typedef struct WalUsage
int64 wal_records; /* # of WAL records produced */
int64 wal_fpi; /* # of WAL full page images produced */
uint64 wal_bytes; /* size of WAL records produced */
int64 wal_buffers_full; /* # of times the WAL buffers became full */
} WalUsage;
/* Flag bits included in InstrAlloc's instrument_options bitmask */

1
src/include/pgstat.h
View File

@ -495,7 +495,6 @@ typedef struct PgStat_WalStats
*/
typedef struct PgStat_PendingWalStats
{
PgStat_Counter wal_buffers_full;
PgStat_Counter wal_write;
PgStat_Counter wal_sync;
instr_time wal_write_time;