Hi,
I added xlogreader cache stats (hits/misses) to pg_stat_wal in
ReadPageInternal() for some of my work and ran some tests with logical
replication subscribers. I had expected that the new stats generated
by walsenders serving the subscribers would be accumulated and shown
via pg_stat_wal view in another session, but that didn't happen. Upon
looking around, I thought adding
pgstat_flush_wal()/pgstat_report_wal() around proc_exit() in
walsener.c might work, but that didn't help either. Can anyone please
let me know why the stats that I added aren't shown via pg_stat_wal
view despite the walsender doing pgstat_initialize() ->
pgstat_init_wal()? Am I missing something?
I'm attaching here with the patch that I was using.
--
Bharath Rupireddy
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
From 6bee81b6284d1619d6828e521d1d210ae5505034 Mon Sep 17 00:00:00 2001
From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Date: Mon, 19 Sep 2022 13:11:31 +0000
Subject: [PATCH v1] Add xlogreader cache stats
---
src/backend/access/transam/xlogreader.c | 9 +++++++++
src/backend/catalog/system_views.sql | 4 +++-
src/backend/utils/activity/pgstat_wal.c | 2 ++
src/backend/utils/adt/pgstatfuncs.c | 9 +++++++--
src/include/catalog/pg_proc.dat | 6 +++---
src/include/pgstat.h | 2 ++
src/test/regress/expected/rules.out | 6 ++++--
7 files changed, 30 insertions(+), 8 deletions(-)
diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
index 050d2f424e..9a5b3d7893 100644
--- a/src/backend/access/transam/xlogreader.c
+++ b/src/backend/access/transam/xlogreader.c
@@ -1000,7 +1000,16 @@ ReadPageInternal(XLogReaderState *state, XLogRecPtr pageptr, int reqLen)
/* check whether we have all the requested data already */
if (targetSegNo == state->seg.ws_segno &&
targetPageOff == state->segoff && reqLen <= state->readLen)
+ {
+#ifndef FRONTEND
+ PendingWalStats.xlogreader_cache_hits++;
+#endif
return state->readLen;
+ }
+
+#ifndef FRONTEND
+ PendingWalStats.xlogreader_cache_misses++;
+#endif
/*
* Invalidate contents of internal buffer before read attempt. Just set
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 55f7ec79e0..0baab55e6b 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1124,7 +1124,9 @@ CREATE VIEW pg_stat_wal AS
w.wal_sync,
w.wal_write_time,
w.wal_sync_time,
- w.stats_reset
+ w.stats_reset,
+ w.xlogreader_cache_hits,
+ w.xlogreader_cache_misses
FROM pg_stat_get_wal() w;
CREATE VIEW pg_stat_progress_analyze AS
diff --git a/src/backend/utils/activity/pgstat_wal.c b/src/backend/utils/activity/pgstat_wal.c
index 5a878bd115..ba97d71471 100644
--- a/src/backend/utils/activity/pgstat_wal.c
+++ b/src/backend/utils/activity/pgstat_wal.c
@@ -105,6 +105,8 @@ pgstat_flush_wal(bool nowait)
WALSTAT_ACC(wal_sync);
WALSTAT_ACC(wal_write_time);
WALSTAT_ACC(wal_sync_time);
+ WALSTAT_ACC(xlogreader_cache_hits);
+ WALSTAT_ACC(xlogreader_cache_misses);
#undef WALSTAT_ACC
LWLockRelease(&stats_shmem->lock);
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index be15b4b2e5..c65c7c08a8 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1732,7 +1732,7 @@ pg_stat_get_buf_alloc(PG_FUNCTION_ARGS)
Datum
pg_stat_get_wal(PG_FUNCTION_ARGS)
{
-#define PG_STAT_GET_WAL_COLS 9
+#define PG_STAT_GET_WAL_COLS 11
TupleDesc tupdesc;
Datum values[PG_STAT_GET_WAL_COLS] = {0};
bool nulls[PG_STAT_GET_WAL_COLS] = {0};
@@ -1759,7 +1759,10 @@ pg_stat_get_wal(PG_FUNCTION_ARGS)
FLOAT8OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 9, "stats_reset",
TIMESTAMPTZOID, -1, 0);
-
+ TupleDescInitEntry(tupdesc, (AttrNumber) 10, "xlogreader_cache_hits",
+ INT8OID, -1, 0);
+ TupleDescInitEntry(tupdesc, (AttrNumber) 11, "xlogreader_cache_misses",
+ INT8OID, -1, 0);
BlessTupleDesc(tupdesc);
/* Get statistics about WAL activity */
@@ -1785,6 +1788,8 @@ pg_stat_get_wal(PG_FUNCTION_ARGS)
values[7] = Float8GetDatum(((double) wal_stats->wal_sync_time) / 1000.0);
values[8] = TimestampTzGetDatum(wal_stats->stat_reset_timestamp);
+ values[9] = Int64GetDatum(wal_stats->xlogreader_cache_hits);
+ values[10] = Int64GetDatum(wal_stats->xlogreader_cache_misses);
/* Returns the record as Datum */
PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index a07e737a33..f728406061 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5649,9 +5649,9 @@
{ oid => '1136', descr => 'statistics: information about WAL activity',
proname => 'pg_stat_get_wal', proisstrict => 'f', provolatile => 's',
proparallel => 'r', prorettype => 'record', proargtypes => '',
- proallargtypes => '{int8,int8,numeric,int8,int8,int8,float8,float8,timestamptz}',
- proargmodes => '{o,o,o,o,o,o,o,o,o}',
- proargnames => '{wal_records,wal_fpi,wal_bytes,wal_buffers_full,wal_write,wal_sync,wal_write_time,wal_sync_time,stats_reset}',
+ proallargtypes => '{int8,int8,numeric,int8,int8,int8,float8,float8,timestamptz,int8,int8}',
+ proargmodes => '{o,o,o,o,o,o,o,o,o,o,o}',
+ proargnames => '{wal_records,wal_fpi,wal_bytes,wal_buffers_full,wal_write,wal_sync,wal_write_time,wal_sync_time,stats_reset,xlogreader_cache_hits,xlogreader_cache_misses}',
prosrc => 'pg_stat_get_wal' },
{ oid => '6248', descr => 'statistics: information about WAL prefetching',
proname => 'pg_stat_get_recovery_prefetch', prorows => '1', proretset => 't',
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index ac28f813b4..f8a60f8a9e 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -393,6 +393,8 @@ typedef struct PgStat_WalStats
PgStat_Counter wal_write_time;
PgStat_Counter wal_sync_time;
TimestampTz stat_reset_timestamp;
+ PgStat_Counter xlogreader_cache_hits;
+ PgStat_Counter xlogreader_cache_misses;
} PgStat_WalStats;
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 9dd137415e..b8c8c98a4c 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -2188,8 +2188,10 @@ pg_stat_wal| SELECT w.wal_records,
w.wal_sync,
w.wal_write_time,
w.wal_sync_time,
- w.stats_reset
- FROM pg_stat_get_wal() w(wal_records, wal_fpi, wal_bytes, wal_buffers_full, wal_write, wal_sync, wal_write_time, wal_sync_time, stats_reset);
+ w.stats_reset,
+ w.xlogreader_cache_hits,
+ w.xlogreader_cache_misses
+ FROM pg_stat_get_wal() w(wal_records, wal_fpi, wal_bytes, wal_buffers_full, wal_write, wal_sync, wal_write_time, wal_sync_time, stats_reset, xlogreader_cache_hits, xlogreader_cache_misses);
pg_stat_wal_receiver| SELECT s.pid,
s.status,
s.receive_start_lsn,
--
2.34.1
