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Add wal_fpi_bytes to pg_stat_wal and pg_stat_get_backend_wal()

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This new counter, called "wal_fpi_bytes", tracks the total amount in
bytes of full page images (FPIs) generated in WAL.  This data becomes
available globally via pg_stat_wal, and for backend statistics via
pg_stat_get_backend_wal().

Previously, this information could only be retrieved with pg_waldump or
pg_walinspect, which may not be available depending on the environment,
and are expensive to execute.  It offers hints about how much FPIs
impact the WAL generated, which could be a large percentage for some
workloads, as well as the effects of wal_compression or page holes.

Bump catalog version.
Bump PGSTAT_FILE_FORMAT_ID, due to the addition of wal_fpi_bytes in
PgStat_WalCounters.

Author: Shinya Kato <shinya11.kato@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/CAOzEurQtZEAfg6P0kU3Wa-f9BWQOi0RzJEMPN56wNTOmJLmfaQ@mail.gmail.com
This commit is contained in:
Michael Paquier
2025-10-28 16:21:51 +09:00
parent 3e8e05596a
commit f9a09aa295
12 changed files with 46 additions and 15 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
src/backend/access/transam/xloginsert.c
View File

@@ -33,12 +33,14 @@
#include "access/xloginsert.h"
#include "catalog/pg_control.h"
#include "common/pg_lzcompress.h"
#include "executor/instrument.h"
#include "miscadmin.h"
#include "pg_trace.h"
#include "replication/origin.h"
#include "storage/bufmgr.h"
#include "storage/proc.h"
#include "utils/memutils.h"
#include "utils/pgstat_internal.h"
/*
* Guess the maximum buffer size required to store a compressed version of
@@ -796,6 +798,10 @@ XLogRecordAssemble(RmgrId rmid, uint8 info,
}
total_len += bimg.length;
/* Track the WAL full page images in bytes */
pgWalUsage.wal_fpi_bytes += bimg.length;
pgstat_report_fixed = true;
}
if (needs_data)

1
src/backend/catalog/system_views.sql
View File

@@ -1221,6 +1221,7 @@ CREATE VIEW pg_stat_wal AS
w.wal_records,
w.wal_fpi,
w.wal_bytes,
w.wal_fpi_bytes,
w.wal_buffers_full,
w.stats_reset
FROM pg_stat_get_wal() w;

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_fpi_bytes += add->wal_fpi_bytes;
dst->wal_buffers_full += add->wal_buffers_full;
}
@@ -289,5 +290,6 @@ 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_fpi_bytes += add->wal_fpi_bytes - sub->wal_fpi_bytes;
dst->wal_buffers_full += add->wal_buffers_full - sub->wal_buffers_full;
}

1
src/backend/utils/activity/pgstat_backend.c
View File

@@ -252,6 +252,7 @@ pgstat_flush_backend_entry_wal(PgStat_EntryRef *entry_ref)
WALSTAT_ACC(wal_records, wal_usage_diff);
WALSTAT_ACC(wal_fpi, wal_usage_diff);
WALSTAT_ACC(wal_bytes, wal_usage_diff);
WALSTAT_ACC(wal_fpi_bytes, wal_usage_diff);
#undef WALSTAT_ACC
/*

1
src/backend/utils/activity/pgstat_wal.c
View File

@@ -121,6 +121,7 @@ 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_fpi_bytes, wal_usage_diff);
WALSTAT_ACC(wal_buffers_full, wal_usage_diff);
#undef WALSTAT_ACC

20
src/backend/utils/adt/pgstatfuncs.c
View File

@@ -1637,7 +1637,7 @@ static Datum
pg_stat_wal_build_tuple(PgStat_WalCounters wal_counters,
TimestampTz stat_reset_timestamp)
{
#define PG_STAT_WAL_COLS 5
#define PG_STAT_WAL_COLS 6
TupleDesc tupdesc;
Datum values[PG_STAT_WAL_COLS] = {0};
bool nulls[PG_STAT_WAL_COLS] = {0};
@@ -1651,9 +1651,11 @@ pg_stat_wal_build_tuple(PgStat_WalCounters wal_counters,
INT8OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 3, "wal_bytes",
NUMERICOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 4, "wal_buffers_full",
TupleDescInitEntry(tupdesc, (AttrNumber) 4, "wal_fpi_bytes",
NUMERICOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 5, "wal_buffers_full",
INT8OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 5, "stats_reset",
TupleDescInitEntry(tupdesc, (AttrNumber) 6, "stats_reset",
TIMESTAMPTZOID, -1, 0);
BlessTupleDesc(tupdesc);
@@ -1669,12 +1671,18 @@ pg_stat_wal_build_tuple(PgStat_WalCounters wal_counters,
ObjectIdGetDatum(0),
Int32GetDatum(-1));
values[3] = Int64GetDatum(wal_counters.wal_buffers_full);
snprintf(buf, sizeof buf, UINT64_FORMAT, wal_counters.wal_fpi_bytes);
values[3] = DirectFunctionCall3(numeric_in,
CStringGetDatum(buf),
ObjectIdGetDatum(0),
Int32GetDatum(-1));
values[4] = Int64GetDatum(wal_counters.wal_buffers_full);
if (stat_reset_timestamp != 0)
values[4] = TimestampTzGetDatum(stat_reset_timestamp);
values[5] = TimestampTzGetDatum(stat_reset_timestamp);
else
nulls[4] = true;
nulls[5] = true;
/* Returns the record as Datum */
PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));