Move wal_buffers_full from PgStat_PendingWalStats to WalUsage

michaelpq · michaelpq · commit eaf502747bac · 2025-02-17T13:14:28.000+09:00
wal_buffers_full has been introduced in pg_stat_wal in 8d9a935, as some information providing metrics for the tuning of the GUC wal_buffers. WalUsage has been introduced before that in df3b181. 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
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
@@ -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();
 				}
 			}
diff --git a/src/backend/executor/instrument.c b/src/backend/executor/instrument.c
@@ -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;
 }
diff --git a/src/backend/utils/activity/pgstat_wal.c b/src/backend/utils/activity/pgstat_wal.c
@@ -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);
diff --git a/src/include/executor/instrument.h b/src/include/executor/instrument.h
@@ -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 */
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
@@ -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;

Original file line number	Diff line number	Diff line change
`@@ -2093,7 +2093,7 @@ AdvanceXLInsertBuffer(XLogRecPtr upto, TimeLineID tli, bool opportunistic)`
`2093`	`2093`	`WriteRqst.Flush = 0;`
`2094`	`2094`	`XLogWrite(WriteRqst, tli, false);`
`2095`	`2095`	`LWLockRelease(WALWriteLock);`
`2096`		`- PendingWalStats.wal_buffers_full++;`
	`2096`	`+ pgWalUsage.wal_buffers_full++;`
`2097`	`2097`	`TRACE_POSTGRESQL_WAL_BUFFER_WRITE_DIRTY_DONE();`
`2098`	`2098`	`}`
`2099`	`2099`	`}`
Original file line number	Diff line number	Diff line change
`@@ -280,6 +280,7 @@ WalUsageAdd(WalUsage dst, WalUsage add)`
`280`	`280`	`dst->wal_bytes += add->wal_bytes;`
`281`	`281`	`dst->wal_records += add->wal_records;`
`282`	`282`	`dst->wal_fpi += add->wal_fpi;`
	`283`	`+ dst->wal_buffers_full += add->wal_buffers_full;`
`283`	`284`	`}`
`284`	`285`
`285`	`286`	`void`
`@@ -288,4 +289,5 @@ WalUsageAccumDiff(WalUsage dst, const WalUsage add, const WalUsage *sub)`
`288`	`289`	`dst->wal_bytes += add->wal_bytes - sub->wal_bytes;`
`289`	`290`	`dst->wal_records += add->wal_records - sub->wal_records;`
`290`	`291`	`dst->wal_fpi += add->wal_fpi - sub->wal_fpi;`
	`292`	`+ dst->wal_buffers_full += add->wal_buffers_full - sub->wal_buffers_full;`
`291`	`293`	`}`
Original file line number	Diff line number	Diff line change
`@@ -495,7 +495,6 @@ typedef struct PgStat_WalStats`
`495`	`495`	`*/`
`496`	`496`	`typedef struct PgStat_PendingWalStats`
`497`	`497`	`{`
`498`		`- PgStat_Counter wal_buffers_full;`
`499`	`498`	`PgStat_Counter wal_write;`
`500`	`499`	`PgStat_Counter wal_sync;`
`501`	`500`	`instr_time wal_write_time;`