From b16a0ccada3c2acc80bf733e71935677b9ab6382 Mon Sep 17 00:00:00 2001
From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Date: Tue, 25 Feb 2025 10:18:05 +0000
Subject: [PATCH v1] Flush the IO statistics of active walsenders

The walsender does not flush its IO statistics until it exits.
The issue is there since pg_stat_io has been introduced in a9c70b46dbe.
This commits:

1. ensures it does not wait to exit to flush its IO statistics
2. adds a test
---
 src/backend/replication/walsender.c               |  7 +++++++
 .../recovery/t/035_standby_logical_decoding.pl    | 15 +++++++++++++++
 2 files changed, 22 insertions(+)
  26.2% src/backend/replication/
  73.7% src/test/recovery/t/

diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 446d10c1a7d..3664d7d0c75 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -90,6 +90,7 @@
 #include "utils/guc.h"
 #include "utils/memutils.h"
 #include "utils/pg_lsn.h"
+#include "utils/pgstat_internal.h"
 #include "utils/ps_status.h"
 #include "utils/timeout.h"
 #include "utils/timestamp.h"
@@ -2793,6 +2794,12 @@ WalSndLoop(WalSndSendDataCallback send_data)
 		if (pq_flush_if_writable() != 0)
 			WalSndShutdown();
 
+		/*
+		 * Report IO statistics
+		 */
+		pgstat_flush_io(false);
+		(void) pgstat_flush_backend(false, PGSTAT_BACKEND_FLUSH_IO);
+
 		/* If nothing remains to be sent right now ... */
 		if (WalSndCaughtUp && !pq_is_send_pending())
 		{
diff --git a/src/test/recovery/t/035_standby_logical_decoding.pl b/src/test/recovery/t/035_standby_logical_decoding.pl
index 8903177d883..ab34d290165 100644
--- a/src/test/recovery/t/035_standby_logical_decoding.pl
+++ b/src/test/recovery/t/035_standby_logical_decoding.pl
@@ -543,6 +543,9 @@ $node_subscriber->stop;
 reactive_slots_change_hfs_and_wait_for_xmins('behaves_ok_', 'vacuum_full_',
 	0, 1);
 
+# To check that an active walsender updates its IO statistics below.
+$node_standby->safe_psql('testdb', "SELECT pg_stat_reset_shared('io')");
+
 # Ensure that replication slot stats are not empty before triggering the
 # conflict.
 $node_primary->safe_psql('testdb',
@@ -552,6 +555,18 @@ $node_standby->poll_query_until('testdb',
 	qq[SELECT total_txns > 0 FROM pg_stat_replication_slots WHERE slot_name = 'vacuum_full_activeslot']
 ) or die "replication slot stats of vacuum_full_activeslot not updated";
 
+# Ensure an active walsender updates its IO statistics.
+is( $node_standby->safe_psql(
+		'testdb',
+		qq(SELECT reads > 0
+		FROM pg_catalog.pg_stat_io
+		WHERE backend_type = 'walsender'
+		AND object = 'relation'
+		AND context = 'normal')
+	),
+	qq(t),
+	"Check that an active walsender updates its IO statistics");
+
 # This should trigger the conflict
 wait_until_vacuum_can_remove(
 	'full', 'CREATE TABLE conflict_test(x integer, y text);
-- 
2.34.1