Remove wal_[sync|write][_time] from pg_stat_wal and track_wal_io_timing

From 7b2492de4fbf30ab971e0e1637accee5f7f6e67b Mon Sep 17 00:00:00 2001
From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Date: Tue, 18 Feb 2025 07:14:05 +0000
Subject: [PATCH v2 1/2] Add details in the pg_stat_io doc about the wal object

Adding details about writes, fsyncs, write_time and sync_time when linked
to the wal object.
---
 doc/src/sgml/monitoring.sgml | 9 +++++++++
 1 file changed, 9 insertions(+)
 100.0% doc/src/sgml/

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 928a6eb64b0..151d69cd0b3 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -2959,6 +2959,15 @@ description | Waiting for a newly initialized WAL file to reach durable storage
       linkend="wal-configuration"/>.
      </para>
     </listitem>
+    <listitem>
+     <para>
+      For the WAL <structfield>object</structfield>, <varname>fsyncs</varname>
+      and <varname>sync_time</varname> track the sync activity of WAL files via
+      issue_xlog_fsync(). <varname>writes</varname> and <varname>write_time</varname>
+      track the write activity of WAL files via XLogWrite().
+      See <xref linkend="wal-configuration"/> for more information.
+     </para>
+    </listitem>
    </itemizedlist>
   </para>
 
-- 
2.34.1

From f36afdf6630c7eb116284a5932c9b9e0b565ecba Mon Sep 17 00:00:00 2001
From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Date: Tue, 18 Feb 2025 07:58:24 +0000
Subject: [PATCH v2 2/2] Remove wal_[sync|write][_time] from pg_stat_wal and
 track_wal_io_timing

a051e71e28a added this information into pg_stat_io (with more details and
granularity), so there is no need to keep it in pg_stat_wal. This also
allows to remove PendingWalStats and simplifies up coming commits related
to per backend WAL statistics. Once done, track_wal_io_timing becomes useless
so it is also removed.

In passing remove the pgstat_prepare_io_time() parameter now that
track_wal_io_timing is gone.
---
 doc/src/sgml/config.sgml                      | 22 -------
 doc/src/sgml/monitoring.sgml                  | 62 -------------------
 doc/src/sgml/wal.sgml                         | 12 ++--
 src/backend/access/transam/xlog.c             | 42 ++-----------
 src/backend/access/transam/xlogreader.c       |  2 +-
 src/backend/access/transam/xlogrecovery.c     |  2 +-
 src/backend/catalog/system_views.sql          |  4 --
 src/backend/storage/buffer/bufmgr.c           | 10 +--
 src/backend/storage/buffer/localbuf.c         |  4 +-
 src/backend/storage/smgr/md.c                 |  4 +-
 src/backend/utils/activity/pgstat_io.c        |  7 +--
 src/backend/utils/activity/pgstat_wal.c       | 24 +------
 src/backend/utils/adt/pgstatfuncs.c           | 20 +-----
 src/backend/utils/misc/guc_tables.c           |  9 ---
 src/backend/utils/misc/postgresql.conf.sample |  1 -
 src/include/access/xlog.h                     |  1 -
 src/include/catalog/pg_proc.dat               |  6 +-
 src/include/pgstat.h                          | 30 +--------
 src/test/regress/expected/rules.out           |  6 +-
 src/tools/pgindent/typedefs.list              |  1 -
 20 files changed, 36 insertions(+), 233 deletions(-)
  41.6% doc/src/sgml/
  14.0% src/backend/access/transam/
   6.0% src/backend/storage/buffer/
  11.9% src/backend/utils/activity/
   9.0% src/backend/utils/adt/
   4.6% src/backend/
  10.6% src/include/

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 9eedcf6f0f4..6d7b15d9f1e 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -8367,28 +8367,6 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
       </listitem>
      </varlistentry>
 
-     <varlistentry id="guc-track-wal-io-timing" xreflabel="track_wal_io_timing">
-      <term><varname>track_wal_io_timing</varname> (<type>boolean</type>)
-      <indexterm>
-       <primary><varname>track_wal_io_timing</varname> configuration parameter</primary>
-      </indexterm>
-      </term>
-      <listitem>
-       <para>
-        Enables timing of WAL I/O calls. This parameter is off by default,
-        as it will repeatedly query the operating system for the current time,
-        which may cause significant overhead on some platforms.
-        You can use the <application>pg_test_timing</application> tool to
-        measure the overhead of timing on your system.
-        I/O timing information is
-        displayed in <link linkend="monitoring-pg-stat-wal-view">
-        <structname>pg_stat_wal</structname></link>.
-        Only superusers and users with the appropriate <literal>SET</literal>
-        privilege can change this setting.
-       </para>
-      </listitem>
-     </varlistentry>
-
      <varlistentry id="guc-track-functions" xreflabel="track_functions">
       <term><varname>track_functions</varname> (<type>enum</type>)
       <indexterm>
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 151d69cd0b3..0a0f2a56ea4 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -183,11 +183,6 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
    of block read, write, extend, and fsync times.
   </para>
 
-  <para>
-   The parameter <xref linkend="guc-track-wal-io-timing"/> enables monitoring
-   of WAL write and fsync times.
-  </para>
-
   <para>
    Normally these parameters are set in <filename>postgresql.conf</filename> so
    that they apply to all server processes, but it is possible to turn
@@ -3264,63 +3259,6 @@ description | Waiting for a newly initialized WAL file to reach durable storage
       </para></entry>
      </row>
 
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>wal_write</structfield> <type>bigint</type>
-      </para>
-      <para>
-       Number of times WAL buffers were written out to disk via
-       <function>XLogWrite</function> request.
-       See <xref linkend="wal-configuration"/> for more information about
-       the internal WAL function <function>XLogWrite</function>.
-      </para></entry>
-     </row>
-
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>wal_sync</structfield> <type>bigint</type>
-      </para>
-      <para>
-       Number of times WAL files were synced to disk via
-       <function>issue_xlog_fsync</function> request
-       (if <xref linkend="guc-fsync"/> is <literal>on</literal> and
-       <xref linkend="guc-wal-sync-method"/> is either
-       <literal>fdatasync</literal>, <literal>fsync</literal> or
-       <literal>fsync_writethrough</literal>, otherwise zero).
-       See <xref linkend="wal-configuration"/> for more information about
-       the internal WAL function <function>issue_xlog_fsync</function>.
-      </para></entry>
-     </row>
-
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>wal_write_time</structfield> <type>double precision</type>
-      </para>
-      <para>
-       Total amount of time spent writing WAL buffers to disk via
-       <function>XLogWrite</function> request, in milliseconds
-       (if <xref linkend="guc-track-wal-io-timing"/> is enabled,
-       otherwise zero).  This includes the sync time when
-       <varname>wal_sync_method</varname> is either
-       <literal>open_datasync</literal> or <literal>open_sync</literal>.
-      </para></entry>
-     </row>
-
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>wal_sync_time</structfield> <type>double precision</type>
-      </para>
-      <para>
-       Total amount of time spent syncing WAL files to disk via
-       <function>issue_xlog_fsync</function> request, in milliseconds
-       (if <varname>track_wal_io_timing</varname> is enabled,
-       <varname>fsync</varname> is <literal>on</literal>, and
-       <varname>wal_sync_method</varname> is either
-       <literal>fdatasync</literal>, <literal>fsync</literal> or
-       <literal>fsync_writethrough</literal>, otherwise zero).
-      </para></entry>
-     </row>
-
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
diff --git a/doc/src/sgml/wal.sgml b/doc/src/sgml/wal.sgml
index b908720adea..8a5ef49c1b5 100644
--- a/doc/src/sgml/wal.sgml
+++ b/doc/src/sgml/wal.sgml
@@ -810,11 +810,11 @@
   <para>
    There are two internal functions to write WAL data to disk:
    <function>XLogWrite</function> and <function>issue_xlog_fsync</function>.
-   When <xref linkend="guc-track-wal-io-timing"/> is enabled, the total
+   When <xref linkend="guc-track-io-timing"/> is enabled, the total
    amounts of time <function>XLogWrite</function> writes and
    <function>issue_xlog_fsync</function> syncs WAL data to disk are counted as
-   <literal>wal_write_time</literal> and <literal>wal_sync_time</literal> in
-   <xref linkend="pg-stat-wal-view"/>, respectively.
+   <literal>write_time</literal> and <literal>sync_time</literal> in
+   <xref linkend="pg-stat-io-view"/> for the WAL <literal>object</literal>, respectively.
    <function>XLogWrite</function> is normally called by
    <function>XLogInsertRecord</function> (when there is no space for the new
    record in WAL buffers), <function>XLogFlush</function> and the WAL writer,
@@ -829,11 +829,11 @@
    <literal>fsync</literal>, or <literal>fsync_writethrough</literal>,
    the write operation moves WAL buffers to kernel cache and
    <function>issue_xlog_fsync</function> syncs them to disk. Regardless
-   of the setting of <varname>track_wal_io_timing</varname>, the number
+   of the setting of <varname>track_io_timing</varname>, the number
    of times <function>XLogWrite</function> writes and
    <function>issue_xlog_fsync</function> syncs WAL data to disk are also
-   counted as <literal>wal_write</literal> and <literal>wal_sync</literal>
-   in <structname>pg_stat_wal</structname>, respectively.
+   counted as <literal>writes</literal> and <literal>fsyncs</literal>
+   in <structname>pg_stat_io</structname> for the WAL <literal>object</literal>, respectively.
   </para>
 
   <para>
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f9bf5ba7509..f1516664f5f 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -134,7 +134,6 @@ int			CommitSiblings = 5; /* # concurrent xacts needed to sleep */
 int			wal_retrieve_retry_interval = 5000;
 int			max_slot_wal_keep_size_mb = -1;
 int			wal_decode_buffer_size = 512 * 1024;
-bool		track_wal_io_timing = false;
 
 #ifdef WAL_DEBUG
 bool		XLOG_DEBUG = false;
@@ -2436,10 +2435,9 @@ XLogWrite(XLogwrtRqst WriteRqst, TimeLineID tli, bool flexible)
 				errno = 0;
 
 				/*
-				 * Measure I/O timing to write WAL data, for pg_stat_io and/or
-				 * pg_stat_wal.
+				 * Measure I/O timing to write WAL data, for pg_stat_io.
 				 */
-				start = pgstat_prepare_io_time(track_io_timing || track_wal_io_timing);
+				start = pgstat_prepare_io_time();
 
 				pgstat_report_wait_start(WAIT_EVENT_WAL_WRITE);
 				written = pg_pwrite(openLogFile, from, nleft, startoffset);
@@ -2448,20 +2446,6 @@ XLogWrite(XLogwrtRqst WriteRqst, TimeLineID tli, bool flexible)
 				pgstat_count_io_op_time(IOOBJECT_WAL, IOCONTEXT_NORMAL,
 										IOOP_WRITE, start, 1, written);
 
-				/*
-				 * Increment the I/O timing and the number of times WAL data
-				 * were written out to disk.
-				 */
-				if (track_wal_io_timing)
-				{
-					instr_time	end;
-
-					INSTR_TIME_SET_CURRENT(end);
-					INSTR_TIME_ACCUM_DIFF(PendingWalStats.wal_write_time, end, start);
-				}
-
-				PendingWalStats.wal_write++;
-
 				if (written <= 0)
 				{
 					char		xlogfname[MAXFNAMELEN];
@@ -3264,7 +3248,7 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
 				 errmsg("could not create file \"%s\": %m", tmppath)));
 
 	/* Measure I/O timing when initializing segment */
-	io_start = pgstat_prepare_io_time(track_io_timing);
+	io_start = pgstat_prepare_io_time();
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_WRITE);
 	save_errno = 0;
@@ -3326,7 +3310,7 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
 	}
 
 	/* Measure I/O timing when flushing segment */
-	io_start = pgstat_prepare_io_time(track_io_timing);
+	io_start = pgstat_prepare_io_time();
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_SYNC);
 	if (pg_fsync(fd) != 0)
@@ -8718,10 +8702,9 @@ issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
 		return;
 
 	/*
-	 * Measure I/O timing to sync the WAL file for pg_stat_io and/or
-	 * pg_stat_wal.
+	 * Measure I/O timing to sync the WAL file for pg_stat_io.
 	 */
-	start = pgstat_prepare_io_time(track_io_timing || track_wal_io_timing);
+	start = pgstat_prepare_io_time();
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_SYNC);
 	switch (wal_sync_method)
@@ -8767,21 +8750,8 @@ issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
 
 	pgstat_report_wait_end();
 
-	/*
-	 * Increment the I/O timing and the number of times WAL files were synced.
-	 */
-	if (track_wal_io_timing)
-	{
-		instr_time	end;
-
-		INSTR_TIME_SET_CURRENT(end);
-		INSTR_TIME_ACCUM_DIFF(PendingWalStats.wal_sync_time, end, start);
-	}
-
 	pgstat_count_io_op_time(IOOBJECT_WAL, IOCONTEXT_NORMAL, IOOP_FSYNC,
 							start, 1, 0);
-
-	PendingWalStats.wal_sync++;
 }
 
 /*
diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
index 31bffc6f501..995e4f7c26f 100644
--- a/src/backend/access/transam/xlogreader.c
+++ b/src/backend/access/transam/xlogreader.c
@@ -1557,7 +1557,7 @@ WALRead(XLogReaderState *state,
 
 #ifndef FRONTEND
 		/* Measure I/O timing when reading segment */
-		io_start = pgstat_prepare_io_time(track_io_timing);
+		io_start = pgstat_prepare_io_time();
 
 		pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
 #endif
diff --git a/src/backend/access/transam/xlogrecovery.c b/src/backend/access/transam/xlogrecovery.c
index 473de6710d7..ac70b73749c 100644
--- a/src/backend/access/transam/xlogrecovery.c
+++ b/src/backend/access/transam/xlogrecovery.c
@@ -3401,7 +3401,7 @@ retry:
 	readOff = targetPageOff;
 
 	/* Measure I/O timing when reading segment */
-	io_start = pgstat_prepare_io_time(track_io_timing);
+	io_start = pgstat_prepare_io_time();
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
 	r = pg_pread(readFile, readBuf, XLOG_BLCKSZ, (off_t) readOff);
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index eff0990957e..a4d2cfdcaf5 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1189,10 +1189,6 @@ CREATE VIEW pg_stat_wal AS
         w.wal_fpi,
         w.wal_bytes,
         w.wal_buffers_full,
-        w.wal_write,
-        w.wal_sync,
-        w.wal_write_time,
-        w.wal_sync_time,
         w.stats_reset
     FROM pg_stat_get_wal() w;
 
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 75cfc2b6fe9..d3216ef6ba7 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -1509,7 +1509,7 @@ WaitReadBuffers(ReadBuffersOperation *operation)
 			io_pages[io_buffers_len++] = BufferGetBlock(buffers[i]);
 		}
 
-		io_start = pgstat_prepare_io_time(track_io_timing);
+		io_start = pgstat_prepare_io_time();
 		smgrreadv(operation->smgr, forknum, io_first_block, io_pages, io_buffers_len);
 		pgstat_count_io_op_time(io_object, io_context, IOOP_READ, io_start,
 								1, io_buffers_len * BLCKSZ);
@@ -2401,7 +2401,7 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
 		}
 	}
 
-	io_start = pgstat_prepare_io_time(track_io_timing);
+	io_start = pgstat_prepare_io_time();
 
 	/*
 	 * Note: if smgrzeroextend fails, we will end up with buffers that are
@@ -3858,7 +3858,7 @@ FlushBuffer(BufferDesc *buf, SMgrRelation reln, IOObject io_object,
 	 */
 	bufToWrite = PageSetChecksumCopy((Page) bufBlock, buf->tag.blockNum);
 
-	io_start = pgstat_prepare_io_time(track_io_timing);
+	io_start = pgstat_prepare_io_time();
 
 	/*
 	 * bufToWrite is either the shared buffer or a copy, as appropriate.
@@ -4460,7 +4460,7 @@ FlushRelationBuffers(Relation rel)
 
 				PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);
 
-				io_start = pgstat_prepare_io_time(track_io_timing);
+				io_start = pgstat_prepare_io_time();
 
 				smgrwrite(srel,
 						  BufTagGetForkNum(&bufHdr->tag),
@@ -5917,7 +5917,7 @@ IssuePendingWritebacks(WritebackContext *wb_context, IOContext io_context)
 	sort_pending_writebacks(wb_context->pending_writebacks,
 							wb_context->nr_pending);
 
-	io_start = pgstat_prepare_io_time(track_io_timing);
+	io_start = pgstat_prepare_io_time();
 
 	/*
 	 * Coalesce neighbouring writes, but nothing else. For that we iterate
diff --git a/src/backend/storage/buffer/localbuf.c b/src/backend/storage/buffer/localbuf.c
index 64931efaa75..78b65fb160a 100644
--- a/src/backend/storage/buffer/localbuf.c
+++ b/src/backend/storage/buffer/localbuf.c
@@ -244,7 +244,7 @@ GetLocalVictimBuffer(void)
 
 		PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);
 
-		io_start = pgstat_prepare_io_time(track_io_timing);
+		io_start = pgstat_prepare_io_time();
 
 		/* And write... */
 		smgrwrite(oreln,
@@ -414,7 +414,7 @@ ExtendBufferedRelLocal(BufferManagerRelation bmr,
 		}
 	}
 
-	io_start = pgstat_prepare_io_time(track_io_timing);
+	io_start = pgstat_prepare_io_time();
 
 	/* actually extend relation */
 	smgrzeroextend(bmr.smgr, fork, first_block, extend_by, false);
diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
index 7bf0b45e2c3..298754d1b64 100644
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -1381,7 +1381,7 @@ register_dirty_segment(SMgrRelation reln, ForkNumber forknum, MdfdVec *seg)
 		ereport(DEBUG1,
 				(errmsg_internal("could not forward fsync request because request queue is full")));
 
-		io_start = pgstat_prepare_io_time(track_io_timing);
+		io_start = pgstat_prepare_io_time();
 
 		if (FileSync(seg->mdfd_vfd, WAIT_EVENT_DATA_FILE_SYNC) < 0)
 			ereport(data_sync_elevel(ERROR),
@@ -1786,7 +1786,7 @@ mdsyncfiletag(const FileTag *ftag, char *path)
 		need_to_close = true;
 	}
 
-	io_start = pgstat_prepare_io_time(track_io_timing);
+	io_start = pgstat_prepare_io_time();
 
 	/* Sync the file. */
 	result = FileSync(file, WAIT_EVENT_DATA_FILE_SYNC);
diff --git a/src/backend/utils/activity/pgstat_io.c b/src/backend/utils/activity/pgstat_io.c
index 28a431084b8..e7362b52a37 100644
--- a/src/backend/utils/activity/pgstat_io.c
+++ b/src/backend/utils/activity/pgstat_io.c
@@ -83,15 +83,14 @@ pgstat_count_io_op(IOObject io_object, IOContext io_context, IOOp io_op,
 }
 
 /*
- * Initialize the internal timing for an IO operation, depending on an
- * IO timing GUC.
+ * Initialize the internal timing for an IO operation.
  */
 instr_time
-pgstat_prepare_io_time(bool track_io_guc)
+pgstat_prepare_io_time(void)
 {
 	instr_time	io_start;
 
-	if (track_io_guc)
+	if (track_io_timing)
 		INSTR_TIME_SET_CURRENT(io_start);
 	else
 	{
diff --git a/src/backend/utils/activity/pgstat_wal.c b/src/backend/utils/activity/pgstat_wal.c
index c1ca65eb991..4dc41a4a590 100644
--- a/src/backend/utils/activity/pgstat_wal.c
+++ b/src/backend/utils/activity/pgstat_wal.c
@@ -21,8 +21,6 @@
 #include "utils/pgstat_internal.h"
 
 
-PgStat_PendingWalStats PendingWalStats = {0};
-
 /*
  * WAL usage counters saved from pgWalUsage at the previous call to
  * pgstat_report_wal(). This is used to calculate how much WAL usage
@@ -118,17 +116,10 @@ pgstat_wal_flush_cb(bool nowait)
 
 #define WALSTAT_ACC(fld, var_to_add) \
 	(stats_shmem->stats.fld += var_to_add.fld)
-#define WALSTAT_ACC_INSTR_TIME(fld) \
-	(stats_shmem->stats.fld += INSTR_TIME_GET_MICROSEC(PendingWalStats.fld))
 	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, wal_usage_diff);
-	WALSTAT_ACC(wal_write, PendingWalStats);
-	WALSTAT_ACC(wal_sync, PendingWalStats);
-	WALSTAT_ACC_INSTR_TIME(wal_write_time);
-	WALSTAT_ACC_INSTR_TIME(wal_sync_time);
-#undef WALSTAT_ACC_INSTR_TIME
 #undef WALSTAT_ACC
 
 	LWLockRelease(&stats_shmem->lock);
@@ -138,11 +129,6 @@ pgstat_wal_flush_cb(bool nowait)
 	 */
 	prevWalUsage = pgWalUsage;
 
-	/*
-	 * Clear out the statistics buffer, so it can be re-used.
-	 */
-	MemSet(&PendingWalStats, 0, sizeof(PendingWalStats));
-
 	return false;
 }
 
@@ -158,18 +144,12 @@ pgstat_wal_init_backend_cb(void)
 }
 
 /*
- * To determine whether any WAL activity has occurred since last time, not
- * only the number of generated WAL records but also the numbers of WAL
- * writes and syncs need to be checked. Because even transaction that
- * generates no WAL records can write or sync WAL data when flushing the
- * data pages.
+ * To determine whether WAL usage happened.
  */
 bool
 pgstat_wal_have_pending_cb(void)
 {
-	return pgWalUsage.wal_records != prevWalUsage.wal_records ||
-		PendingWalStats.wal_write != 0 ||
-		PendingWalStats.wal_sync != 0;
+	return pgWalUsage.wal_records != prevWalUsage.wal_records;
 }
 
 void
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index e9096a88492..68e16e52ab6 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1637,7 +1637,7 @@ pg_stat_get_backend_io(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_wal(PG_FUNCTION_ARGS)
 {
-#define PG_STAT_GET_WAL_COLS	9
+#define PG_STAT_GET_WAL_COLS	5
 	TupleDesc	tupdesc;
 	Datum		values[PG_STAT_GET_WAL_COLS] = {0};
 	bool		nulls[PG_STAT_GET_WAL_COLS] = {0};
@@ -1654,15 +1654,7 @@ pg_stat_get_wal(PG_FUNCTION_ARGS)
 					   NUMERICOID, -1, 0);
 	TupleDescInitEntry(tupdesc, (AttrNumber) 4, "wal_buffers_full",
 					   INT8OID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 5, "wal_write",
-					   INT8OID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 6, "wal_sync",
-					   INT8OID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 7, "wal_write_time",
-					   FLOAT8OID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 8, "wal_sync_time",
-					   FLOAT8OID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 9, "stats_reset",
+	TupleDescInitEntry(tupdesc, (AttrNumber) 5, "stats_reset",
 					   TIMESTAMPTZOID, -1, 0);
 
 	BlessTupleDesc(tupdesc);
@@ -1682,14 +1674,8 @@ pg_stat_get_wal(PG_FUNCTION_ARGS)
 									Int32GetDatum(-1));
 
 	values[3] = Int64GetDatum(wal_stats->wal_buffers_full);
-	values[4] = Int64GetDatum(wal_stats->wal_write);
-	values[5] = Int64GetDatum(wal_stats->wal_sync);
-
-	/* Convert counters from microsec to millisec for display */
-	values[6] = Float8GetDatum(((double) wal_stats->wal_write_time) / 1000.0);
-	values[7] = Float8GetDatum(((double) wal_stats->wal_sync_time) / 1000.0);
 
-	values[8] = TimestampTzGetDatum(wal_stats->stat_reset_timestamp);
+	values[4] = TimestampTzGetDatum(wal_stats->stat_reset_timestamp);
 
 	/* Returns the record as Datum */
 	PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 3cde94a1759..e323b75379a 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -1499,15 +1499,6 @@ struct config_bool ConfigureNamesBool[] =
 		false,
 		NULL, NULL, NULL
 	},
-	{
-		{"track_wal_io_timing", PGC_SUSET, STATS_CUMULATIVE,
-			gettext_noop("Collects timing statistics for WAL I/O activity."),
-			NULL
-		},
-		&track_wal_io_timing,
-		false,
-		NULL, NULL, NULL
-	},
 
 	{
 		{"update_process_title", PGC_SUSET, PROCESS_TITLE,
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 415f253096c..bd03540bcef 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -638,7 +638,6 @@
 #track_counts = on
 #track_cost_delay_timing = off
 #track_io_timing = off
-#track_wal_io_timing = off
 #track_functions = none			# none, pl, all
 #stats_fetch_consistency = cache	# cache, none, snapshot
 
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index 4411c1468ac..bd18d95a6cf 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -54,7 +54,6 @@ extern PGDLLIMPORT char *wal_consistency_checking_string;
 extern PGDLLIMPORT bool log_checkpoints;
 extern PGDLLIMPORT int CommitDelay;
 extern PGDLLIMPORT int CommitSiblings;
-extern PGDLLIMPORT bool track_wal_io_timing;
 extern PGDLLIMPORT int wal_decode_buffer_size;
 
 extern PGDLLIMPORT int CheckPointSegments;
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 9e803d610d7..1e1626964e3 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5950,9 +5950,9 @@
 { 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,timestamptz}',
+  proargmodes => '{o,o,o,o,o}',
+  proargnames => '{wal_records,wal_fpi,wal_bytes,wal_buffers_full,stats_reset}',
   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 53f2a8458e6..030b101028f 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -480,28 +480,9 @@ typedef struct PgStat_WalStats
 	PgStat_Counter wal_fpi;
 	uint64		wal_bytes;
 	PgStat_Counter wal_buffers_full;
-	PgStat_Counter wal_write;
-	PgStat_Counter wal_sync;
-	PgStat_Counter wal_write_time;
-	PgStat_Counter wal_sync_time;
 	TimestampTz stat_reset_timestamp;
 } PgStat_WalStats;
 
-/*
- * This struct stores wal-related durations as instr_time, which makes it
- * cheaper and easier to accumulate them, by not requiring type
- * conversions. During stats flush instr_time will be converted into
- * microseconds.
- */
-typedef struct PgStat_PendingWalStats
-{
-	PgStat_Counter wal_write;
-	PgStat_Counter wal_sync;
-	instr_time	wal_write_time;
-	instr_time	wal_sync_time;
-} PgStat_PendingWalStats;
-
-
 /*
  * Functions in pgstat.c
  */
@@ -583,7 +564,7 @@ extern bool pgstat_bktype_io_stats_valid(PgStat_BktypeIO *backend_io,
 										 BackendType bktype);
 extern void pgstat_count_io_op(IOObject io_object, IOContext io_context,
 							   IOOp io_op, uint32 cnt, uint64 bytes);
-extern instr_time pgstat_prepare_io_time(bool track_io_guc);
+extern instr_time pgstat_prepare_io_time(void);
 extern void pgstat_count_io_op_time(IOObject io_object, IOContext io_context,
 									IOOp io_op, instr_time start_time,
 									uint32 cnt, uint64 bytes);
@@ -834,13 +815,4 @@ extern PGDLLIMPORT PgStat_Counter pgStatTransactionIdleTime;
 /* updated by the traffic cop and in errfinish() */
 extern PGDLLIMPORT SessionEndType pgStatSessionEndCause;
 
-
-/*
- * Variables in pgstat_wal.c
- */
-
-/* updated directly by backends and background processes */
-extern PGDLLIMPORT PgStat_PendingWalStats PendingWalStats;
-
-
 #endif							/* PGSTAT_H */
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 5baba8d39ff..62f69ac20b2 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -2259,12 +2259,8 @@ pg_stat_wal| SELECT wal_records,
     wal_fpi,
     wal_bytes,
     wal_buffers_full,
-    wal_write,
-    wal_sync,
-    wal_write_time,
-    wal_sync_time,
     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);
+   FROM pg_stat_get_wal() w(wal_records, wal_fpi, wal_bytes, wal_buffers_full, stats_reset);
 pg_stat_wal_receiver| SELECT pid,
     status,
     receive_start_lsn,
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 64c6bf7a891..c86156d4718 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2164,7 +2164,6 @@ PgStat_KindInfo
 PgStat_LocalState
 PgStat_PendingDroppedStatsItem
 PgStat_PendingIO
-PgStat_PendingWalStats
 PgStat_SLRUStats
 PgStat_ShmemControl
 PgStat_Snapshot
-- 
2.34.1

From b54bfecceff1f5eda6b6cfed0fa9874c7ffa0edd Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Thu, 20 Feb 2025 14:30:40 +0900
Subject: [PATCH v3] Remove wal_[sync|write][_time] from pg_stat_wal and
 track_wal_io_timing

a051e71e28a added this information into pg_stat_io (with more details and
granularity), so there is no need to keep it in pg_stat_wal. This also
allows to remove PendingWalStats and simplifies up coming commits related
to per backend WAL statistics. Once done, track_wal_io_timing becomes useless
so it is also removed.

In passing remove the pgstat_prepare_io_time() parameter now that
track_wal_io_timing is gone.
---
 src/include/access/xlog.h                     |  1 -
 src/include/catalog/pg_proc.dat               |  6 +-
 src/include/pgstat.h                          | 30 +--------
 src/backend/access/transam/xlog.c             | 42 ++-----------
 src/backend/access/transam/xlogreader.c       |  2 +-
 src/backend/access/transam/xlogrecovery.c     |  2 +-
 src/backend/catalog/system_views.sql          |  4 --
 src/backend/storage/buffer/bufmgr.c           | 10 +--
 src/backend/storage/buffer/localbuf.c         |  4 +-
 src/backend/storage/smgr/md.c                 |  4 +-
 src/backend/utils/activity/pgstat_io.c        |  7 +--
 src/backend/utils/activity/pgstat_wal.c       | 24 +------
 src/backend/utils/adt/pgstatfuncs.c           | 20 +-----
 src/backend/utils/misc/guc_tables.c           |  9 ---
 src/backend/utils/misc/postgresql.conf.sample |  1 -
 src/test/regress/expected/rules.out           |  6 +-
 doc/src/sgml/config.sgml                      | 22 -------
 doc/src/sgml/monitoring.sgml                  | 62 -------------------
 src/tools/pgindent/typedefs.list              |  1 -
 19 files changed, 30 insertions(+), 227 deletions(-)

diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index 4411c1468aca..bd18d95a6cf8 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -54,7 +54,6 @@ extern PGDLLIMPORT char *wal_consistency_checking_string;
 extern PGDLLIMPORT bool log_checkpoints;
 extern PGDLLIMPORT int CommitDelay;
 extern PGDLLIMPORT int CommitSiblings;
-extern PGDLLIMPORT bool track_wal_io_timing;
 extern PGDLLIMPORT int wal_decode_buffer_size;
 
 extern PGDLLIMPORT int CheckPointSegments;
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 9e803d610d7b..1e1626964e3b 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5950,9 +5950,9 @@
 { 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,timestamptz}',
+  proargmodes => '{o,o,o,o,o}',
+  proargnames => '{wal_records,wal_fpi,wal_bytes,wal_buffers_full,stats_reset}',
   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 53f2a8458e6f..030b101028f7 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -480,28 +480,9 @@ typedef struct PgStat_WalStats
 	PgStat_Counter wal_fpi;
 	uint64		wal_bytes;
 	PgStat_Counter wal_buffers_full;
-	PgStat_Counter wal_write;
-	PgStat_Counter wal_sync;
-	PgStat_Counter wal_write_time;
-	PgStat_Counter wal_sync_time;
 	TimestampTz stat_reset_timestamp;
 } PgStat_WalStats;
 
-/*
- * This struct stores wal-related durations as instr_time, which makes it
- * cheaper and easier to accumulate them, by not requiring type
- * conversions. During stats flush instr_time will be converted into
- * microseconds.
- */
-typedef struct PgStat_PendingWalStats
-{
-	PgStat_Counter wal_write;
-	PgStat_Counter wal_sync;
-	instr_time	wal_write_time;
-	instr_time	wal_sync_time;
-} PgStat_PendingWalStats;
-
-
 /*
  * Functions in pgstat.c
  */
@@ -583,7 +564,7 @@ extern bool pgstat_bktype_io_stats_valid(PgStat_BktypeIO *backend_io,
 										 BackendType bktype);
 extern void pgstat_count_io_op(IOObject io_object, IOContext io_context,
 							   IOOp io_op, uint32 cnt, uint64 bytes);
-extern instr_time pgstat_prepare_io_time(bool track_io_guc);
+extern instr_time pgstat_prepare_io_time(void);
 extern void pgstat_count_io_op_time(IOObject io_object, IOContext io_context,
 									IOOp io_op, instr_time start_time,
 									uint32 cnt, uint64 bytes);
@@ -834,13 +815,4 @@ extern PGDLLIMPORT PgStat_Counter pgStatTransactionIdleTime;
 /* updated by the traffic cop and in errfinish() */
 extern PGDLLIMPORT SessionEndType pgStatSessionEndCause;
 
-
-/*
- * Variables in pgstat_wal.c
- */
-
-/* updated directly by backends and background processes */
-extern PGDLLIMPORT PgStat_PendingWalStats PendingWalStats;
-
-
 #endif							/* PGSTAT_H */
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f9bf5ba75091..f1516664f5fa 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -134,7 +134,6 @@ int			CommitSiblings = 5; /* # concurrent xacts needed to sleep */
 int			wal_retrieve_retry_interval = 5000;
 int			max_slot_wal_keep_size_mb = -1;
 int			wal_decode_buffer_size = 512 * 1024;
-bool		track_wal_io_timing = false;
 
 #ifdef WAL_DEBUG
 bool		XLOG_DEBUG = false;
@@ -2436,10 +2435,9 @@ XLogWrite(XLogwrtRqst WriteRqst, TimeLineID tli, bool flexible)
 				errno = 0;
 
 				/*
-				 * Measure I/O timing to write WAL data, for pg_stat_io and/or
-				 * pg_stat_wal.
+				 * Measure I/O timing to write WAL data, for pg_stat_io.
 				 */
-				start = pgstat_prepare_io_time(track_io_timing || track_wal_io_timing);
+				start = pgstat_prepare_io_time();
 
 				pgstat_report_wait_start(WAIT_EVENT_WAL_WRITE);
 				written = pg_pwrite(openLogFile, from, nleft, startoffset);
@@ -2448,20 +2446,6 @@ XLogWrite(XLogwrtRqst WriteRqst, TimeLineID tli, bool flexible)
 				pgstat_count_io_op_time(IOOBJECT_WAL, IOCONTEXT_NORMAL,
 										IOOP_WRITE, start, 1, written);
 
-				/*
-				 * Increment the I/O timing and the number of times WAL data
-				 * were written out to disk.
-				 */
-				if (track_wal_io_timing)
-				{
-					instr_time	end;
-
-					INSTR_TIME_SET_CURRENT(end);
-					INSTR_TIME_ACCUM_DIFF(PendingWalStats.wal_write_time, end, start);
-				}
-
-				PendingWalStats.wal_write++;
-
 				if (written <= 0)
 				{
 					char		xlogfname[MAXFNAMELEN];
@@ -3264,7 +3248,7 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
 				 errmsg("could not create file \"%s\": %m", tmppath)));
 
 	/* Measure I/O timing when initializing segment */
-	io_start = pgstat_prepare_io_time(track_io_timing);
+	io_start = pgstat_prepare_io_time();
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_WRITE);
 	save_errno = 0;
@@ -3326,7 +3310,7 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
 	}
 
 	/* Measure I/O timing when flushing segment */
-	io_start = pgstat_prepare_io_time(track_io_timing);
+	io_start = pgstat_prepare_io_time();
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_SYNC);
 	if (pg_fsync(fd) != 0)
@@ -8718,10 +8702,9 @@ issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
 		return;
 
 	/*
-	 * Measure I/O timing to sync the WAL file for pg_stat_io and/or
-	 * pg_stat_wal.
+	 * Measure I/O timing to sync the WAL file for pg_stat_io.
 	 */
-	start = pgstat_prepare_io_time(track_io_timing || track_wal_io_timing);
+	start = pgstat_prepare_io_time();
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_SYNC);
 	switch (wal_sync_method)
@@ -8767,21 +8750,8 @@ issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
 
 	pgstat_report_wait_end();
 
-	/*
-	 * Increment the I/O timing and the number of times WAL files were synced.
-	 */
-	if (track_wal_io_timing)
-	{
-		instr_time	end;
-
-		INSTR_TIME_SET_CURRENT(end);
-		INSTR_TIME_ACCUM_DIFF(PendingWalStats.wal_sync_time, end, start);
-	}
-
 	pgstat_count_io_op_time(IOOBJECT_WAL, IOCONTEXT_NORMAL, IOOP_FSYNC,
 							start, 1, 0);
-
-	PendingWalStats.wal_sync++;
 }
 
 /*
diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
index 31bffc6f5019..995e4f7c26fd 100644
--- a/src/backend/access/transam/xlogreader.c
+++ b/src/backend/access/transam/xlogreader.c
@@ -1557,7 +1557,7 @@ WALRead(XLogReaderState *state,
 
 #ifndef FRONTEND
 		/* Measure I/O timing when reading segment */
-		io_start = pgstat_prepare_io_time(track_io_timing);
+		io_start = pgstat_prepare_io_time();
 
 		pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
 #endif
diff --git a/src/backend/access/transam/xlogrecovery.c b/src/backend/access/transam/xlogrecovery.c
index f234007d3484..915cb330295c 100644
--- a/src/backend/access/transam/xlogrecovery.c
+++ b/src/backend/access/transam/xlogrecovery.c
@@ -3401,7 +3401,7 @@ retry:
 	readOff = targetPageOff;
 
 	/* Measure I/O timing when reading segment */
-	io_start = pgstat_prepare_io_time(track_io_timing);
+	io_start = pgstat_prepare_io_time();
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
 	r = pg_pread(readFile, readBuf, XLOG_BLCKSZ, (off_t) readOff);
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index eff0990957eb..a4d2cfdcaf5d 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1189,10 +1189,6 @@ CREATE VIEW pg_stat_wal AS
         w.wal_fpi,
         w.wal_bytes,
         w.wal_buffers_full,
-        w.wal_write,
-        w.wal_sync,
-        w.wal_write_time,
-        w.wal_sync_time,
         w.stats_reset
     FROM pg_stat_get_wal() w;
 
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 75cfc2b6fe96..d3216ef6ba75 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -1509,7 +1509,7 @@ WaitReadBuffers(ReadBuffersOperation *operation)
 			io_pages[io_buffers_len++] = BufferGetBlock(buffers[i]);
 		}
 
-		io_start = pgstat_prepare_io_time(track_io_timing);
+		io_start = pgstat_prepare_io_time();
 		smgrreadv(operation->smgr, forknum, io_first_block, io_pages, io_buffers_len);
 		pgstat_count_io_op_time(io_object, io_context, IOOP_READ, io_start,
 								1, io_buffers_len * BLCKSZ);
@@ -2401,7 +2401,7 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
 		}
 	}
 
-	io_start = pgstat_prepare_io_time(track_io_timing);
+	io_start = pgstat_prepare_io_time();
 
 	/*
 	 * Note: if smgrzeroextend fails, we will end up with buffers that are
@@ -3858,7 +3858,7 @@ FlushBuffer(BufferDesc *buf, SMgrRelation reln, IOObject io_object,
 	 */
 	bufToWrite = PageSetChecksumCopy((Page) bufBlock, buf->tag.blockNum);
 
-	io_start = pgstat_prepare_io_time(track_io_timing);
+	io_start = pgstat_prepare_io_time();
 
 	/*
 	 * bufToWrite is either the shared buffer or a copy, as appropriate.
@@ -4460,7 +4460,7 @@ FlushRelationBuffers(Relation rel)
 
 				PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);
 
-				io_start = pgstat_prepare_io_time(track_io_timing);
+				io_start = pgstat_prepare_io_time();
 
 				smgrwrite(srel,
 						  BufTagGetForkNum(&bufHdr->tag),
@@ -5917,7 +5917,7 @@ IssuePendingWritebacks(WritebackContext *wb_context, IOContext io_context)
 	sort_pending_writebacks(wb_context->pending_writebacks,
 							wb_context->nr_pending);
 
-	io_start = pgstat_prepare_io_time(track_io_timing);
+	io_start = pgstat_prepare_io_time();
 
 	/*
 	 * Coalesce neighbouring writes, but nothing else. For that we iterate
diff --git a/src/backend/storage/buffer/localbuf.c b/src/backend/storage/buffer/localbuf.c
index 64931efaa756..78b65fb160ad 100644
--- a/src/backend/storage/buffer/localbuf.c
+++ b/src/backend/storage/buffer/localbuf.c
@@ -244,7 +244,7 @@ GetLocalVictimBuffer(void)
 
 		PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);
 
-		io_start = pgstat_prepare_io_time(track_io_timing);
+		io_start = pgstat_prepare_io_time();
 
 		/* And write... */
 		smgrwrite(oreln,
@@ -414,7 +414,7 @@ ExtendBufferedRelLocal(BufferManagerRelation bmr,
 		}
 	}
 
-	io_start = pgstat_prepare_io_time(track_io_timing);
+	io_start = pgstat_prepare_io_time();
 
 	/* actually extend relation */
 	smgrzeroextend(bmr.smgr, fork, first_block, extend_by, false);
diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
index 7bf0b45e2c34..298754d1b64a 100644
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -1381,7 +1381,7 @@ register_dirty_segment(SMgrRelation reln, ForkNumber forknum, MdfdVec *seg)
 		ereport(DEBUG1,
 				(errmsg_internal("could not forward fsync request because request queue is full")));
 
-		io_start = pgstat_prepare_io_time(track_io_timing);
+		io_start = pgstat_prepare_io_time();
 
 		if (FileSync(seg->mdfd_vfd, WAIT_EVENT_DATA_FILE_SYNC) < 0)
 			ereport(data_sync_elevel(ERROR),
@@ -1786,7 +1786,7 @@ mdsyncfiletag(const FileTag *ftag, char *path)
 		need_to_close = true;
 	}
 
-	io_start = pgstat_prepare_io_time(track_io_timing);
+	io_start = pgstat_prepare_io_time();
 
 	/* Sync the file. */
 	result = FileSync(file, WAIT_EVENT_DATA_FILE_SYNC);
diff --git a/src/backend/utils/activity/pgstat_io.c b/src/backend/utils/activity/pgstat_io.c
index 28a431084b89..e7362b52a37b 100644
--- a/src/backend/utils/activity/pgstat_io.c
+++ b/src/backend/utils/activity/pgstat_io.c
@@ -83,15 +83,14 @@ pgstat_count_io_op(IOObject io_object, IOContext io_context, IOOp io_op,
 }
 
 /*
- * Initialize the internal timing for an IO operation, depending on an
- * IO timing GUC.
+ * Initialize the internal timing for an IO operation.
  */
 instr_time
-pgstat_prepare_io_time(bool track_io_guc)
+pgstat_prepare_io_time(void)
 {
 	instr_time	io_start;
 
-	if (track_io_guc)
+	if (track_io_timing)
 		INSTR_TIME_SET_CURRENT(io_start);
 	else
 	{
diff --git a/src/backend/utils/activity/pgstat_wal.c b/src/backend/utils/activity/pgstat_wal.c
index c1ca65eb9918..4dc41a4a590e 100644
--- a/src/backend/utils/activity/pgstat_wal.c
+++ b/src/backend/utils/activity/pgstat_wal.c
@@ -21,8 +21,6 @@
 #include "utils/pgstat_internal.h"
 
 
-PgStat_PendingWalStats PendingWalStats = {0};
-
 /*
  * WAL usage counters saved from pgWalUsage at the previous call to
  * pgstat_report_wal(). This is used to calculate how much WAL usage
@@ -118,17 +116,10 @@ pgstat_wal_flush_cb(bool nowait)
 
 #define WALSTAT_ACC(fld, var_to_add) \
 	(stats_shmem->stats.fld += var_to_add.fld)
-#define WALSTAT_ACC_INSTR_TIME(fld) \
-	(stats_shmem->stats.fld += INSTR_TIME_GET_MICROSEC(PendingWalStats.fld))
 	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, wal_usage_diff);
-	WALSTAT_ACC(wal_write, PendingWalStats);
-	WALSTAT_ACC(wal_sync, PendingWalStats);
-	WALSTAT_ACC_INSTR_TIME(wal_write_time);
-	WALSTAT_ACC_INSTR_TIME(wal_sync_time);
-#undef WALSTAT_ACC_INSTR_TIME
 #undef WALSTAT_ACC
 
 	LWLockRelease(&stats_shmem->lock);
@@ -138,11 +129,6 @@ pgstat_wal_flush_cb(bool nowait)
 	 */
 	prevWalUsage = pgWalUsage;
 
-	/*
-	 * Clear out the statistics buffer, so it can be re-used.
-	 */
-	MemSet(&PendingWalStats, 0, sizeof(PendingWalStats));
-
 	return false;
 }
 
@@ -158,18 +144,12 @@ pgstat_wal_init_backend_cb(void)
 }
 
 /*
- * To determine whether any WAL activity has occurred since last time, not
- * only the number of generated WAL records but also the numbers of WAL
- * writes and syncs need to be checked. Because even transaction that
- * generates no WAL records can write or sync WAL data when flushing the
- * data pages.
+ * To determine whether WAL usage happened.
  */
 bool
 pgstat_wal_have_pending_cb(void)
 {
-	return pgWalUsage.wal_records != prevWalUsage.wal_records ||
-		PendingWalStats.wal_write != 0 ||
-		PendingWalStats.wal_sync != 0;
+	return pgWalUsage.wal_records != prevWalUsage.wal_records;
 }
 
 void
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index e9096a88492c..68e16e52ab6d 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1637,7 +1637,7 @@ pg_stat_get_backend_io(PG_FUNCTION_ARGS)
 Datum
 pg_stat_get_wal(PG_FUNCTION_ARGS)
 {
-#define PG_STAT_GET_WAL_COLS	9
+#define PG_STAT_GET_WAL_COLS	5
 	TupleDesc	tupdesc;
 	Datum		values[PG_STAT_GET_WAL_COLS] = {0};
 	bool		nulls[PG_STAT_GET_WAL_COLS] = {0};
@@ -1654,15 +1654,7 @@ pg_stat_get_wal(PG_FUNCTION_ARGS)
 					   NUMERICOID, -1, 0);
 	TupleDescInitEntry(tupdesc, (AttrNumber) 4, "wal_buffers_full",
 					   INT8OID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 5, "wal_write",
-					   INT8OID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 6, "wal_sync",
-					   INT8OID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 7, "wal_write_time",
-					   FLOAT8OID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 8, "wal_sync_time",
-					   FLOAT8OID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 9, "stats_reset",
+	TupleDescInitEntry(tupdesc, (AttrNumber) 5, "stats_reset",
 					   TIMESTAMPTZOID, -1, 0);
 
 	BlessTupleDesc(tupdesc);
@@ -1682,14 +1674,8 @@ pg_stat_get_wal(PG_FUNCTION_ARGS)
 									Int32GetDatum(-1));
 
 	values[3] = Int64GetDatum(wal_stats->wal_buffers_full);
-	values[4] = Int64GetDatum(wal_stats->wal_write);
-	values[5] = Int64GetDatum(wal_stats->wal_sync);
 
-	/* Convert counters from microsec to millisec for display */
-	values[6] = Float8GetDatum(((double) wal_stats->wal_write_time) / 1000.0);
-	values[7] = Float8GetDatum(((double) wal_stats->wal_sync_time) / 1000.0);
-
-	values[8] = TimestampTzGetDatum(wal_stats->stat_reset_timestamp);
+	values[4] = TimestampTzGetDatum(wal_stats->stat_reset_timestamp);
 
 	/* Returns the record as Datum */
 	PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 3cde94a17595..e323b75379ac 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -1499,15 +1499,6 @@ struct config_bool ConfigureNamesBool[] =
 		false,
 		NULL, NULL, NULL
 	},
-	{
-		{"track_wal_io_timing", PGC_SUSET, STATS_CUMULATIVE,
-			gettext_noop("Collects timing statistics for WAL I/O activity."),
-			NULL
-		},
-		&track_wal_io_timing,
-		false,
-		NULL, NULL, NULL
-	},
 
 	{
 		{"update_process_title", PGC_SUSET, PROCESS_TITLE,
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 415f253096c1..bd03540bceff 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -638,7 +638,6 @@
 #track_counts = on
 #track_cost_delay_timing = off
 #track_io_timing = off
-#track_wal_io_timing = off
 #track_functions = none			# none, pl, all
 #stats_fetch_consistency = cache	# cache, none, snapshot
 
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 5baba8d39ff6..62f69ac20b2e 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -2259,12 +2259,8 @@ pg_stat_wal| SELECT wal_records,
     wal_fpi,
     wal_bytes,
     wal_buffers_full,
-    wal_write,
-    wal_sync,
-    wal_write_time,
-    wal_sync_time,
     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);
+   FROM pg_stat_get_wal() w(wal_records, wal_fpi, wal_bytes, wal_buffers_full, stats_reset);
 pg_stat_wal_receiver| SELECT pid,
     status,
     receive_start_lsn,
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 9eedcf6f0f41..6d7b15d9f1e4 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -8367,28 +8367,6 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
       </listitem>
      </varlistentry>
 
-     <varlistentry id="guc-track-wal-io-timing" xreflabel="track_wal_io_timing">
-      <term><varname>track_wal_io_timing</varname> (<type>boolean</type>)
-      <indexterm>
-       <primary><varname>track_wal_io_timing</varname> configuration parameter</primary>
-      </indexterm>
-      </term>
-      <listitem>
-       <para>
-        Enables timing of WAL I/O calls. This parameter is off by default,
-        as it will repeatedly query the operating system for the current time,
-        which may cause significant overhead on some platforms.
-        You can use the <application>pg_test_timing</application> tool to
-        measure the overhead of timing on your system.
-        I/O timing information is
-        displayed in <link linkend="monitoring-pg-stat-wal-view">
-        <structname>pg_stat_wal</structname></link>.
-        Only superusers and users with the appropriate <literal>SET</literal>
-        privilege can change this setting.
-       </para>
-      </listitem>
-     </varlistentry>
-
      <varlistentry id="guc-track-functions" xreflabel="track_functions">
       <term><varname>track_functions</varname> (<type>enum</type>)
       <indexterm>
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 71c4f96d0544..b8b6311f1467 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -183,11 +183,6 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
    of block read, write, extend, and fsync times.
   </para>
 
-  <para>
-   The parameter <xref linkend="guc-track-wal-io-timing"/> enables monitoring
-   of WAL write and fsync times.
-  </para>
-
   <para>
    Normally these parameters are set in <filename>postgresql.conf</filename> so
    that they apply to all server processes, but it is possible to turn
@@ -3265,63 +3260,6 @@ description | Waiting for a newly initialized WAL file to reach durable storage
       </para></entry>
      </row>
 
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>wal_write</structfield> <type>bigint</type>
-      </para>
-      <para>
-       Number of times WAL buffers were written out to disk via
-       <function>XLogWrite</function> request.
-       See <xref linkend="wal-configuration"/> for more information about
-       the internal WAL function <function>XLogWrite</function>.
-      </para></entry>
-     </row>
-
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>wal_sync</structfield> <type>bigint</type>
-      </para>
-      <para>
-       Number of times WAL files were synced to disk via
-       <function>issue_xlog_fsync</function> request
-       (if <xref linkend="guc-fsync"/> is <literal>on</literal> and
-       <xref linkend="guc-wal-sync-method"/> is either
-       <literal>fdatasync</literal>, <literal>fsync</literal> or
-       <literal>fsync_writethrough</literal>, otherwise zero).
-       See <xref linkend="wal-configuration"/> for more information about
-       the internal WAL function <function>issue_xlog_fsync</function>.
-      </para></entry>
-     </row>
-
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>wal_write_time</structfield> <type>double precision</type>
-      </para>
-      <para>
-       Total amount of time spent writing WAL buffers to disk via
-       <function>XLogWrite</function> request, in milliseconds
-       (if <xref linkend="guc-track-wal-io-timing"/> is enabled,
-       otherwise zero).  This includes the sync time when
-       <varname>wal_sync_method</varname> is either
-       <literal>open_datasync</literal> or <literal>open_sync</literal>.
-      </para></entry>
-     </row>
-
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>wal_sync_time</structfield> <type>double precision</type>
-      </para>
-      <para>
-       Total amount of time spent syncing WAL files to disk via
-       <function>issue_xlog_fsync</function> request, in milliseconds
-       (if <varname>track_wal_io_timing</varname> is enabled,
-       <varname>fsync</varname> is <literal>on</literal>, and
-       <varname>wal_sync_method</varname> is either
-       <literal>fdatasync</literal>, <literal>fsync</literal> or
-       <literal>fsync_writethrough</literal>, otherwise zero).
-      </para></entry>
-     </row>
-
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index fb39c915d76a..f87f304d6fc2 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2165,7 +2165,6 @@ PgStat_KindInfo
 PgStat_LocalState
 PgStat_PendingDroppedStatsItem
 PgStat_PendingIO
-PgStat_PendingWalStats
 PgStat_SLRUStats
 PgStat_ShmemControl
 PgStat_Snapshot
-- 
2.47.2

From 4f1190bbb4e37319be37f69fe1682ec5ef7eb971 Mon Sep 17 00:00:00 2001
From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Date: Mon, 24 Feb 2025 11:29:35 +0000
Subject: [PATCH v1] re-introduce track_wal_io_timing

a051e71e28a added the "timing tracking" in the WAL code path with "only"
track_io_timing enabled (and track_wal_io_timing still false). Then it made
sense for 2421e9a51d2 to get rid of the track_wal_io_timing GUC.

Concerns have been raised about the fact that a051e71e28a added the "timing tracking"
in the WAL code path with "only" track_io_timing enabled. So this commit re-introduces
the track_wal_io_timing GUC and ensure that WAL timing is tracked in pg_stat_io
only if track_io_timing and track_wal_io_timing are both enabled.
---
 doc/src/sgml/config.sgml                      | 25 +++++++++++++++++++
 doc/src/sgml/monitoring.sgml                  |  5 ++++
 src/backend/access/transam/xlog.c             | 21 ++++++++++------
 src/backend/access/transam/xlogreader.c       |  4 +--
 src/backend/access/transam/xlogrecovery.c     |  6 ++---
 src/backend/storage/buffer/bufmgr.c           | 21 ++++++++--------
 src/backend/storage/buffer/localbuf.c         |  8 +++---
 src/backend/storage/smgr/md.c                 |  8 +++---
 src/backend/utils/activity/pgstat_io.c        | 12 +++++----
 src/backend/utils/misc/guc_tables.c           |  9 +++++++
 src/backend/utils/misc/postgresql.conf.sample |  1 +
 src/include/access/xlog.h                     |  1 +
 src/include/pgstat.h                          |  4 +--
 13 files changed, 87 insertions(+), 38 deletions(-)
  25.8% doc/src/sgml/
  24.2% src/backend/access/transam/
  25.8% src/backend/storage/buffer/
   6.9% src/backend/storage/smgr/
   8.2% src/backend/utils/activity/
   4.2% src/backend/utils/misc/
   4.6% src/include/

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index a8354576108..7e7eae01d33 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -8393,6 +8393,31 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-track-wal-io-timing" xreflabel="track_wal_io_timing">
+      <term><varname>track_wal_io_timing</varname> (<type>boolean</type>)
+      <indexterm>
+       <primary><varname>track_wal_io_timing</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Enables timing of WAL I/O write and fsync calls. This parameter is off by
+        default, as it will repeatedly query the operating system for the current time,
+        which may cause significant overhead on some platforms.
+        You can use the <application>pg_test_timing</application> tool to
+        measure the overhead of timing on your system.
+        I/O timing information is
+        displayed in <link linkend="monitoring-pg-stat-io-view">
+        <structname>pg_stat_io</structname></link> and in the output of the
+        <link linkend="pg-stat-get-backend-io">
+        <function>pg_stat_get_backend_io()</function></link> function only if
+        <xref linkend="guc-track-io-timing"/> is also enabled.
+        Only superusers and users with the appropriate <literal>SET</literal>
+        privilege can change this setting.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-track-functions" xreflabel="track_functions">
       <term><varname>track_functions</varname> (<type>enum</type>)
       <indexterm>
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 3dfd059b7ee..6ff8a4ec929 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -183,6 +183,11 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
    of block read, write, extend, and fsync times.
   </para>
 
+  <para>
+   The parameter <xref linkend="guc-track-wal-io-timing"/> enables monitoring
+   of WAL write and fsync times.
+  </para>
+
   <para>
    Normally these parameters are set in <filename>postgresql.conf</filename> so
    that they apply to all server processes, but it is possible to turn
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 919314f8258..9054aed2242 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -134,6 +134,7 @@ int			CommitSiblings = 5; /* # concurrent xacts needed to sleep */
 int			wal_retrieve_retry_interval = 5000;
 int			max_slot_wal_keep_size_mb = -1;
 int			wal_decode_buffer_size = 512 * 1024;
+bool		track_wal_io_timing = false;
 
 #ifdef WAL_DEBUG
 bool		XLOG_DEBUG = false;
@@ -2432,19 +2433,22 @@ XLogWrite(XLogwrtRqst WriteRqst, TimeLineID tli, bool flexible)
 			nleft = nbytes;
 			do
 			{
+				bool		track_timing = track_io_timing && track_wal_io_timing;
+
 				errno = 0;
 
 				/*
 				 * Measure I/O timing to write WAL data, for pg_stat_io.
 				 */
-				start = pgstat_prepare_io_time();
+				start = pgstat_prepare_io_time(track_timing);
 
 				pgstat_report_wait_start(WAIT_EVENT_WAL_WRITE);
 				written = pg_pwrite(openLogFile, from, nleft, startoffset);
 				pgstat_report_wait_end();
 
 				pgstat_count_io_op_time(IOOBJECT_WAL, IOCONTEXT_NORMAL,
-										IOOP_WRITE, start, 1, written);
+										IOOP_WRITE, start, 1, written,
+										track_timing);
 
 				if (written <= 0)
 				{
@@ -3248,7 +3252,7 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
 				 errmsg("could not create file \"%s\": %m", tmppath)));
 
 	/* Measure I/O timing when initializing segment */
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_WRITE);
 	save_errno = 0;
@@ -3291,7 +3295,7 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
 	 */
 	pgstat_count_io_op_time(IOOBJECT_WAL, IOCONTEXT_INIT, IOOP_WRITE,
 							io_start, 1,
-							wal_init_zero ? wal_segment_size : 1);
+							wal_init_zero ? wal_segment_size : 1, track_io_timing);
 
 	if (save_errno)
 	{
@@ -3310,7 +3314,7 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
 	}
 
 	/* Measure I/O timing when flushing segment */
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_SYNC);
 	if (pg_fsync(fd) != 0)
@@ -3325,7 +3329,7 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
 	pgstat_report_wait_end();
 
 	pgstat_count_io_op_time(IOOBJECT_WAL, IOCONTEXT_INIT,
-							IOOP_FSYNC, io_start, 1, 0);
+							IOOP_FSYNC, io_start, 1, 0, track_io_timing);
 
 	if (close(fd) != 0)
 		ereport(ERROR,
@@ -8728,6 +8732,7 @@ void
 issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
 {
 	char	   *msg = NULL;
+	bool		track_timing = track_io_timing && track_wal_io_timing;
 	instr_time	start;
 
 	Assert(tli != 0);
@@ -8744,7 +8749,7 @@ issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
 	/*
 	 * Measure I/O timing to sync the WAL file for pg_stat_io.
 	 */
-	start = pgstat_prepare_io_time();
+	start = pgstat_prepare_io_time(track_timing);
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_SYNC);
 	switch (wal_sync_method)
@@ -8791,7 +8796,7 @@ issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
 	pgstat_report_wait_end();
 
 	pgstat_count_io_op_time(IOOBJECT_WAL, IOCONTEXT_NORMAL, IOOP_FSYNC,
-							start, 1, 0);
+							start, 1, 0, track_timing);
 }
 
 /*
diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
index 995e4f7c26f..d2418243a18 100644
--- a/src/backend/access/transam/xlogreader.c
+++ b/src/backend/access/transam/xlogreader.c
@@ -1557,7 +1557,7 @@ WALRead(XLogReaderState *state,
 
 #ifndef FRONTEND
 		/* Measure I/O timing when reading segment */
-		io_start = pgstat_prepare_io_time();
+		io_start = pgstat_prepare_io_time(track_io_timing);
 
 		pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
 #endif
@@ -1570,7 +1570,7 @@ WALRead(XLogReaderState *state,
 		pgstat_report_wait_end();
 
 		pgstat_count_io_op_time(IOOBJECT_WAL, IOCONTEXT_NORMAL, IOOP_READ,
-								io_start, 1, readbytes);
+								io_start, 1, readbytes, track_io_timing);
 #endif
 
 		if (readbytes <= 0)
diff --git a/src/backend/access/transam/xlogrecovery.c b/src/backend/access/transam/xlogrecovery.c
index 915cb330295..9e177e9716a 100644
--- a/src/backend/access/transam/xlogrecovery.c
+++ b/src/backend/access/transam/xlogrecovery.c
@@ -3401,7 +3401,7 @@ retry:
 	readOff = targetPageOff;
 
 	/* Measure I/O timing when reading segment */
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
 	r = pg_pread(readFile, readBuf, XLOG_BLCKSZ, (off_t) readOff);
@@ -3413,7 +3413,7 @@ retry:
 		pgstat_report_wait_end();
 
 		pgstat_count_io_op_time(IOOBJECT_WAL, IOCONTEXT_NORMAL, IOOP_READ,
-								io_start, 1, r);
+								io_start, 1, r, track_io_timing);
 
 		XLogFileName(fname, curFileTLI, readSegNo, wal_segment_size);
 		if (r < 0)
@@ -3436,7 +3436,7 @@ retry:
 	pgstat_report_wait_end();
 
 	pgstat_count_io_op_time(IOOBJECT_WAL, IOCONTEXT_NORMAL, IOOP_READ,
-							io_start, 1, r);
+							io_start, 1, r, track_io_timing);
 
 	Assert(targetSegNo == readSegNo);
 	Assert(targetPageOff == readOff);
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index d3216ef6ba7..5de9490d439 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -1509,10 +1509,10 @@ WaitReadBuffers(ReadBuffersOperation *operation)
 			io_pages[io_buffers_len++] = BufferGetBlock(buffers[i]);
 		}
 
-		io_start = pgstat_prepare_io_time();
+		io_start = pgstat_prepare_io_time(track_io_timing);
 		smgrreadv(operation->smgr, forknum, io_first_block, io_pages, io_buffers_len);
 		pgstat_count_io_op_time(io_object, io_context, IOOP_READ, io_start,
-								1, io_buffers_len * BLCKSZ);
+								1, io_buffers_len * BLCKSZ, track_io_timing);
 
 		/* Verify each block we read, and terminate the I/O. */
 		for (int j = 0; j < io_buffers_len; ++j)
@@ -2401,7 +2401,7 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
 		}
 	}
 
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	/*
 	 * Note: if smgrzeroextend fails, we will end up with buffers that are
@@ -2426,7 +2426,7 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
 		UnlockRelationForExtension(bmr.rel, ExclusiveLock);
 
 	pgstat_count_io_op_time(IOOBJECT_RELATION, io_context, IOOP_EXTEND,
-							io_start, 1, extend_by * BLCKSZ);
+							io_start, 1, extend_by * BLCKSZ, track_io_timing);
 
 	/* Set BM_VALID, terminate IO, and wake up any waiters */
 	for (uint32 i = 0; i < extend_by; i++)
@@ -3858,7 +3858,7 @@ FlushBuffer(BufferDesc *buf, SMgrRelation reln, IOObject io_object,
 	 */
 	bufToWrite = PageSetChecksumCopy((Page) bufBlock, buf->tag.blockNum);
 
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	/*
 	 * bufToWrite is either the shared buffer or a copy, as appropriate.
@@ -3888,7 +3888,7 @@ FlushBuffer(BufferDesc *buf, SMgrRelation reln, IOObject io_object,
 	 * of a dirty shared buffer (IOCONTEXT_NORMAL IOOP_WRITE).
 	 */
 	pgstat_count_io_op_time(IOOBJECT_RELATION, io_context,
-							IOOP_WRITE, io_start, 1, BLCKSZ);
+							IOOP_WRITE, io_start, 1, BLCKSZ, track_io_timing);
 
 	pgBufferUsage.shared_blks_written++;
 
@@ -4460,7 +4460,7 @@ FlushRelationBuffers(Relation rel)
 
 				PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);
 
-				io_start = pgstat_prepare_io_time();
+				io_start = pgstat_prepare_io_time(track_io_timing);
 
 				smgrwrite(srel,
 						  BufTagGetForkNum(&bufHdr->tag),
@@ -4470,7 +4470,7 @@ FlushRelationBuffers(Relation rel)
 
 				pgstat_count_io_op_time(IOOBJECT_TEMP_RELATION,
 										IOCONTEXT_NORMAL, IOOP_WRITE,
-										io_start, 1, BLCKSZ);
+										io_start, 1, BLCKSZ, track_io_timing);
 
 				buf_state &= ~(BM_DIRTY | BM_JUST_DIRTIED);
 				pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);
@@ -5917,7 +5917,7 @@ IssuePendingWritebacks(WritebackContext *wb_context, IOContext io_context)
 	sort_pending_writebacks(wb_context->pending_writebacks,
 							wb_context->nr_pending);
 
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	/*
 	 * Coalesce neighbouring writes, but nothing else. For that we iterate
@@ -5977,7 +5977,8 @@ IssuePendingWritebacks(WritebackContext *wb_context, IOContext io_context)
 	 * blocks of permanent relations.
 	 */
 	pgstat_count_io_op_time(IOOBJECT_RELATION, io_context,
-							IOOP_WRITEBACK, io_start, wb_context->nr_pending, 0);
+							IOOP_WRITEBACK, io_start, wb_context->nr_pending, 0,
+							track_io_timing);
 
 	wb_context->nr_pending = 0;
 }
diff --git a/src/backend/storage/buffer/localbuf.c b/src/backend/storage/buffer/localbuf.c
index 78b65fb160a..4ca78c412d3 100644
--- a/src/backend/storage/buffer/localbuf.c
+++ b/src/backend/storage/buffer/localbuf.c
@@ -244,7 +244,7 @@ GetLocalVictimBuffer(void)
 
 		PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);
 
-		io_start = pgstat_prepare_io_time();
+		io_start = pgstat_prepare_io_time(track_io_timing);
 
 		/* And write... */
 		smgrwrite(oreln,
@@ -255,7 +255,7 @@ GetLocalVictimBuffer(void)
 
 		/* Temporary table I/O does not use Buffer Access Strategies */
 		pgstat_count_io_op_time(IOOBJECT_TEMP_RELATION, IOCONTEXT_NORMAL,
-								IOOP_WRITE, io_start, 1, BLCKSZ);
+								IOOP_WRITE, io_start, 1, BLCKSZ, track_io_timing);
 
 		/* Mark not-dirty now in case we error out below */
 		buf_state &= ~BM_DIRTY;
@@ -414,13 +414,13 @@ ExtendBufferedRelLocal(BufferManagerRelation bmr,
 		}
 	}
 
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	/* actually extend relation */
 	smgrzeroextend(bmr.smgr, fork, first_block, extend_by, false);
 
 	pgstat_count_io_op_time(IOOBJECT_TEMP_RELATION, IOCONTEXT_NORMAL, IOOP_EXTEND,
-							io_start, 1, extend_by * BLCKSZ);
+							io_start, 1, extend_by * BLCKSZ, track_io_timing);
 
 	for (uint32 i = 0; i < extend_by; i++)
 	{
diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
index 298754d1b64..d6df9f5102a 100644
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -1381,7 +1381,7 @@ register_dirty_segment(SMgrRelation reln, ForkNumber forknum, MdfdVec *seg)
 		ereport(DEBUG1,
 				(errmsg_internal("could not forward fsync request because request queue is full")));
 
-		io_start = pgstat_prepare_io_time();
+		io_start = pgstat_prepare_io_time(track_io_timing);
 
 		if (FileSync(seg->mdfd_vfd, WAIT_EVENT_DATA_FILE_SYNC) < 0)
 			ereport(data_sync_elevel(ERROR),
@@ -1401,7 +1401,7 @@ register_dirty_segment(SMgrRelation reln, ForkNumber forknum, MdfdVec *seg)
 		 * backend fsyncs.
 		 */
 		pgstat_count_io_op_time(IOOBJECT_RELATION, IOCONTEXT_NORMAL,
-								IOOP_FSYNC, io_start, 1, 0);
+								IOOP_FSYNC, io_start, 1, 0, track_io_timing);
 	}
 }
 
@@ -1786,7 +1786,7 @@ mdsyncfiletag(const FileTag *ftag, char *path)
 		need_to_close = true;
 	}
 
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	/* Sync the file. */
 	result = FileSync(file, WAIT_EVENT_DATA_FILE_SYNC);
@@ -1796,7 +1796,7 @@ mdsyncfiletag(const FileTag *ftag, char *path)
 		FileClose(file);
 
 	pgstat_count_io_op_time(IOOBJECT_RELATION, IOCONTEXT_NORMAL,
-							IOOP_FSYNC, io_start, 1, 0);
+							IOOP_FSYNC, io_start, 1, 0, track_io_timing);
 
 	errno = save_errno;
 	return result;
diff --git a/src/backend/utils/activity/pgstat_io.c b/src/backend/utils/activity/pgstat_io.c
index e7362b52a37..3746f9e4bc2 100644
--- a/src/backend/utils/activity/pgstat_io.c
+++ b/src/backend/utils/activity/pgstat_io.c
@@ -83,14 +83,15 @@ pgstat_count_io_op(IOObject io_object, IOContext io_context, IOOp io_op,
 }
 
 /*
- * Initialize the internal timing for an IO operation.
+ * Initialize the internal timing for an IO operation, depending on an
+ * IO timing GUC.
  */
 instr_time
-pgstat_prepare_io_time(void)
+pgstat_prepare_io_time(bool track_io_guc)
 {
 	instr_time	io_start;
 
-	if (track_io_timing)
+	if (track_io_guc)
 		INSTR_TIME_SET_CURRENT(io_start);
 	else
 	{
@@ -117,9 +118,10 @@ pgstat_prepare_io_time(void)
  */
 void
 pgstat_count_io_op_time(IOObject io_object, IOContext io_context, IOOp io_op,
-						instr_time start_time, uint32 cnt, uint64 bytes)
+						instr_time start_time, uint32 cnt, uint64 bytes,
+						bool track_io_guc)
 {
-	if (track_io_timing)
+	if (track_io_guc)
 	{
 		instr_time	io_time;
 
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 3f1c7b1ebf6..03a6dd49154 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -1500,6 +1500,15 @@ struct config_bool ConfigureNamesBool[] =
 		false,
 		NULL, NULL, NULL
 	},
+	{
+		{"track_wal_io_timing", PGC_SUSET, STATS_CUMULATIVE,
+			gettext_noop("Collects timing statistics for WAL I/O activity."),
+			NULL
+		},
+		&track_wal_io_timing,
+		false,
+		NULL, NULL, NULL
+	},
 
 	{
 		{"update_process_title", PGC_SUSET, PROCESS_TITLE,
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index e771d87da1f..5362ff80519 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -641,6 +641,7 @@
 #track_counts = on
 #track_cost_delay_timing = off
 #track_io_timing = off
+#track_wal_io_timing = off
 #track_functions = none			# none, pl, all
 #stats_fetch_consistency = cache	# cache, none, snapshot
 
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index 0a50d160bba..d313099c027 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -54,6 +54,7 @@ extern PGDLLIMPORT char *wal_consistency_checking_string;
 extern PGDLLIMPORT bool log_checkpoints;
 extern PGDLLIMPORT int CommitDelay;
 extern PGDLLIMPORT int CommitSiblings;
+extern PGDLLIMPORT bool track_wal_io_timing;
 extern PGDLLIMPORT int wal_decode_buffer_size;
 
 extern PGDLLIMPORT int CheckPointSegments;
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index fc651d03cf9..1e60e94be90 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -564,10 +564,10 @@ extern bool pgstat_bktype_io_stats_valid(PgStat_BktypeIO *backend_io,
 										 BackendType bktype);
 extern void pgstat_count_io_op(IOObject io_object, IOContext io_context,
 							   IOOp io_op, uint32 cnt, uint64 bytes);
-extern instr_time pgstat_prepare_io_time(void);
+extern instr_time pgstat_prepare_io_time(bool track_io_guc);
 extern void pgstat_count_io_op_time(IOObject io_object, IOContext io_context,
 									IOOp io_op, instr_time start_time,
-									uint32 cnt, uint64 bytes);
+									uint32 cnt, uint64 bytes, bool track_io_guc);
 
 extern PgStat_IO *pgstat_fetch_stat_io(void);
 extern const char *pgstat_get_io_context_name(IOContext io_context);
-- 
2.34.1

From 196f84b8bd8f817b6e21e65de90464d32a27b286 Mon Sep 17 00:00:00 2001
From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Date: Mon, 24 Feb 2025 11:29:35 +0000
Subject: [PATCH v2] re-introduce track_wal_io_timing

a051e71e28a added the "timing tracking" in the WAL code path with "only"
track_io_timing enabled (and track_wal_io_timing still false). Then it made
sense for 2421e9a51d2 to get rid of the track_wal_io_timing GUC.

Concerns have been raised about the fact that a051e71e28a added the "timing tracking"
in the WAL code path with "only" track_io_timing enabled. So this commit re-introduces
the track_wal_io_timing GUC and ensure that WAL timing is tracked in pg_stat_io
only if track_io_timing and track_wal_io_timing are both enabled.
---
 src/include/access/xlog.h                     |  1 +
 src/include/pgstat.h                          |  2 +-
 src/backend/access/transam/xlog.c             |  9 +++---
 src/backend/access/transam/xlogreader.c       |  2 +-
 src/backend/access/transam/xlogrecovery.c     |  2 +-
 src/backend/storage/buffer/bufmgr.c           | 10 +++---
 src/backend/storage/buffer/localbuf.c         |  4 +--
 src/backend/storage/smgr/md.c                 |  4 +--
 src/backend/utils/activity/pgstat_backend.c   |  3 +-
 src/backend/utils/activity/pgstat_io.c        |  9 +++---
 src/backend/utils/misc/guc_tables.c           |  9 ++++++
 src/backend/utils/misc/postgresql.conf.sample |  1 +
 doc/src/sgml/config.sgml                      | 25 +++++++++++++++
 doc/src/sgml/monitoring.sgml                  | 31 ++++++++++++++++---
 doc/src/sgml/wal.sgml                         |  4 +--
 15 files changed, 88 insertions(+), 28 deletions(-)

diff --git src/include/access/xlog.h src/include/access/xlog.h
index 0a50d160bba8..d313099c027f 100644
--- src/include/access/xlog.h
+++ src/include/access/xlog.h
@@ -54,6 +54,7 @@ extern PGDLLIMPORT char *wal_consistency_checking_string;
 extern PGDLLIMPORT bool log_checkpoints;
 extern PGDLLIMPORT int CommitDelay;
 extern PGDLLIMPORT int CommitSiblings;
+extern PGDLLIMPORT bool track_wal_io_timing;
 extern PGDLLIMPORT int wal_decode_buffer_size;
 
 extern PGDLLIMPORT int CheckPointSegments;
diff --git src/include/pgstat.h src/include/pgstat.h
index fc651d03cf97..e64c527265b9 100644
--- src/include/pgstat.h
+++ src/include/pgstat.h
@@ -564,7 +564,7 @@ extern bool pgstat_bktype_io_stats_valid(PgStat_BktypeIO *backend_io,
 										 BackendType bktype);
 extern void pgstat_count_io_op(IOObject io_object, IOContext io_context,
 							   IOOp io_op, uint32 cnt, uint64 bytes);
-extern instr_time pgstat_prepare_io_time(void);
+extern instr_time pgstat_prepare_io_time(bool track_io_guc);
 extern void pgstat_count_io_op_time(IOObject io_object, IOContext io_context,
 									IOOp io_op, instr_time start_time,
 									uint32 cnt, uint64 bytes);
diff --git src/backend/access/transam/xlog.c src/backend/access/transam/xlog.c
index 919314f82587..799fc739e18c 100644
--- src/backend/access/transam/xlog.c
+++ src/backend/access/transam/xlog.c
@@ -134,6 +134,7 @@ int			CommitSiblings = 5; /* # concurrent xacts needed to sleep */
 int			wal_retrieve_retry_interval = 5000;
 int			max_slot_wal_keep_size_mb = -1;
 int			wal_decode_buffer_size = 512 * 1024;
+bool		track_wal_io_timing = false;
 
 #ifdef WAL_DEBUG
 bool		XLOG_DEBUG = false;
@@ -2437,7 +2438,7 @@ XLogWrite(XLogwrtRqst WriteRqst, TimeLineID tli, bool flexible)
 				/*
 				 * Measure I/O timing to write WAL data, for pg_stat_io.
 				 */
-				start = pgstat_prepare_io_time();
+				start = pgstat_prepare_io_time(track_wal_io_timing);
 
 				pgstat_report_wait_start(WAIT_EVENT_WAL_WRITE);
 				written = pg_pwrite(openLogFile, from, nleft, startoffset);
@@ -3248,7 +3249,7 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
 				 errmsg("could not create file \"%s\": %m", tmppath)));
 
 	/* Measure I/O timing when initializing segment */
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_wal_io_timing);
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_WRITE);
 	save_errno = 0;
@@ -3310,7 +3311,7 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
 	}
 
 	/* Measure I/O timing when flushing segment */
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_wal_io_timing);
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_SYNC);
 	if (pg_fsync(fd) != 0)
@@ -8744,7 +8745,7 @@ issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
 	/*
 	 * Measure I/O timing to sync the WAL file for pg_stat_io.
 	 */
-	start = pgstat_prepare_io_time();
+	start = pgstat_prepare_io_time(track_wal_io_timing);
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_SYNC);
 	switch (wal_sync_method)
diff --git src/backend/access/transam/xlogreader.c src/backend/access/transam/xlogreader.c
index 995e4f7c26fd..5483d4f0dd2b 100644
--- src/backend/access/transam/xlogreader.c
+++ src/backend/access/transam/xlogreader.c
@@ -1557,7 +1557,7 @@ WALRead(XLogReaderState *state,
 
 #ifndef FRONTEND
 		/* Measure I/O timing when reading segment */
-		io_start = pgstat_prepare_io_time();
+		io_start = pgstat_prepare_io_time(track_wal_io_timing);
 
 		pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
 #endif
diff --git src/backend/access/transam/xlogrecovery.c src/backend/access/transam/xlogrecovery.c
index 915cb330295c..c5475aaa97a1 100644
--- src/backend/access/transam/xlogrecovery.c
+++ src/backend/access/transam/xlogrecovery.c
@@ -3401,7 +3401,7 @@ retry:
 	readOff = targetPageOff;
 
 	/* Measure I/O timing when reading segment */
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_wal_io_timing);
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
 	r = pg_pread(readFile, readBuf, XLOG_BLCKSZ, (off_t) readOff);
diff --git src/backend/storage/buffer/bufmgr.c src/backend/storage/buffer/bufmgr.c
index d3216ef6ba75..75cfc2b6fe96 100644
--- src/backend/storage/buffer/bufmgr.c
+++ src/backend/storage/buffer/bufmgr.c
@@ -1509,7 +1509,7 @@ WaitReadBuffers(ReadBuffersOperation *operation)
 			io_pages[io_buffers_len++] = BufferGetBlock(buffers[i]);
 		}
 
-		io_start = pgstat_prepare_io_time();
+		io_start = pgstat_prepare_io_time(track_io_timing);
 		smgrreadv(operation->smgr, forknum, io_first_block, io_pages, io_buffers_len);
 		pgstat_count_io_op_time(io_object, io_context, IOOP_READ, io_start,
 								1, io_buffers_len * BLCKSZ);
@@ -2401,7 +2401,7 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
 		}
 	}
 
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	/*
 	 * Note: if smgrzeroextend fails, we will end up with buffers that are
@@ -3858,7 +3858,7 @@ FlushBuffer(BufferDesc *buf, SMgrRelation reln, IOObject io_object,
 	 */
 	bufToWrite = PageSetChecksumCopy((Page) bufBlock, buf->tag.blockNum);
 
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	/*
 	 * bufToWrite is either the shared buffer or a copy, as appropriate.
@@ -4460,7 +4460,7 @@ FlushRelationBuffers(Relation rel)
 
 				PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);
 
-				io_start = pgstat_prepare_io_time();
+				io_start = pgstat_prepare_io_time(track_io_timing);
 
 				smgrwrite(srel,
 						  BufTagGetForkNum(&bufHdr->tag),
@@ -5917,7 +5917,7 @@ IssuePendingWritebacks(WritebackContext *wb_context, IOContext io_context)
 	sort_pending_writebacks(wb_context->pending_writebacks,
 							wb_context->nr_pending);
 
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	/*
 	 * Coalesce neighbouring writes, but nothing else. For that we iterate
diff --git src/backend/storage/buffer/localbuf.c src/backend/storage/buffer/localbuf.c
index 78b65fb160ad..64931efaa756 100644
--- src/backend/storage/buffer/localbuf.c
+++ src/backend/storage/buffer/localbuf.c
@@ -244,7 +244,7 @@ GetLocalVictimBuffer(void)
 
 		PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);
 
-		io_start = pgstat_prepare_io_time();
+		io_start = pgstat_prepare_io_time(track_io_timing);
 
 		/* And write... */
 		smgrwrite(oreln,
@@ -414,7 +414,7 @@ ExtendBufferedRelLocal(BufferManagerRelation bmr,
 		}
 	}
 
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	/* actually extend relation */
 	smgrzeroextend(bmr.smgr, fork, first_block, extend_by, false);
diff --git src/backend/storage/smgr/md.c src/backend/storage/smgr/md.c
index 298754d1b64a..7bf0b45e2c34 100644
--- src/backend/storage/smgr/md.c
+++ src/backend/storage/smgr/md.c
@@ -1381,7 +1381,7 @@ register_dirty_segment(SMgrRelation reln, ForkNumber forknum, MdfdVec *seg)
 		ereport(DEBUG1,
 				(errmsg_internal("could not forward fsync request because request queue is full")));
 
-		io_start = pgstat_prepare_io_time();
+		io_start = pgstat_prepare_io_time(track_io_timing);
 
 		if (FileSync(seg->mdfd_vfd, WAIT_EVENT_DATA_FILE_SYNC) < 0)
 			ereport(data_sync_elevel(ERROR),
@@ -1786,7 +1786,7 @@ mdsyncfiletag(const FileTag *ftag, char *path)
 		need_to_close = true;
 	}
 
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	/* Sync the file. */
 	result = FileSync(file, WAIT_EVENT_DATA_FILE_SYNC);
diff --git src/backend/utils/activity/pgstat_backend.c src/backend/utils/activity/pgstat_backend.c
index 4a667e7019cc..338da73a9a91 100644
--- src/backend/utils/activity/pgstat_backend.c
+++ src/backend/utils/activity/pgstat_backend.c
@@ -24,6 +24,7 @@
 
 #include "postgres.h"
 
+#include "access/xlog.h"
 #include "storage/bufmgr.h"
 #include "utils/memutils.h"
 #include "utils/pgstat_internal.h"
@@ -43,7 +44,7 @@ void
 pgstat_count_backend_io_op_time(IOObject io_object, IOContext io_context,
 								IOOp io_op, instr_time io_time)
 {
-	Assert(track_io_timing);
+	Assert(track_io_timing || track_wal_io_timing);
 
 	if (!pgstat_tracks_backend_bktype(MyBackendType))
 		return;
diff --git src/backend/utils/activity/pgstat_io.c src/backend/utils/activity/pgstat_io.c
index e7362b52a37b..edb489f3a864 100644
--- src/backend/utils/activity/pgstat_io.c
+++ src/backend/utils/activity/pgstat_io.c
@@ -83,14 +83,15 @@ pgstat_count_io_op(IOObject io_object, IOContext io_context, IOOp io_op,
 }
 
 /*
- * Initialize the internal timing for an IO operation.
+ * Initialize the internal timing for an IO operation, depending on an
+ * IO timing GUC.
  */
 instr_time
-pgstat_prepare_io_time(void)
+pgstat_prepare_io_time(bool track_io_guc)
 {
 	instr_time	io_start;
 
-	if (track_io_timing)
+	if (track_io_guc)
 		INSTR_TIME_SET_CURRENT(io_start);
 	else
 	{
@@ -119,7 +120,7 @@ void
 pgstat_count_io_op_time(IOObject io_object, IOContext io_context, IOOp io_op,
 						instr_time start_time, uint32 cnt, uint64 bytes)
 {
-	if (track_io_timing)
+	if (!INSTR_TIME_IS_ZERO(start_time))
 	{
 		instr_time	io_time;
 
diff --git src/backend/utils/misc/guc_tables.c src/backend/utils/misc/guc_tables.c
index 690bf96ef030..ad25cbb39c55 100644
--- src/backend/utils/misc/guc_tables.c
+++ src/backend/utils/misc/guc_tables.c
@@ -1501,6 +1501,15 @@ struct config_bool ConfigureNamesBool[] =
 		false,
 		NULL, NULL, NULL
 	},
+	{
+		{"track_wal_io_timing", PGC_SUSET, STATS_CUMULATIVE,
+			gettext_noop("Collects timing statistics for WAL I/O activity."),
+			NULL
+		},
+		&track_wal_io_timing,
+		false,
+		NULL, NULL, NULL
+	},
 
 	{
 		{"update_process_title", PGC_SUSET, PROCESS_TITLE,
diff --git src/backend/utils/misc/postgresql.conf.sample src/backend/utils/misc/postgresql.conf.sample
index e771d87da1fb..5362ff805195 100644
--- src/backend/utils/misc/postgresql.conf.sample
+++ src/backend/utils/misc/postgresql.conf.sample
@@ -641,6 +641,7 @@
 #track_counts = on
 #track_cost_delay_timing = off
 #track_io_timing = off
+#track_wal_io_timing = off
 #track_functions = none			# none, pl, all
 #stats_fetch_consistency = cache	# cache, none, snapshot
 
diff --git doc/src/sgml/config.sgml doc/src/sgml/config.sgml
index a83545761085..6186648ccaf5 100644
--- doc/src/sgml/config.sgml
+++ doc/src/sgml/config.sgml
@@ -8393,6 +8393,31 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-track-wal-io-timing" xreflabel="track_wal_io_timing">
+      <term><varname>track_wal_io_timing</varname> (<type>boolean</type>)
+      <indexterm>
+       <primary><varname>track_wal_io_timing</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Enables timing of WAL I/O calls. This parameter is off by default,
+        as it will repeatedly query the operating system for the current time,
+        which may cause significant overhead on some platforms.
+        You can use the <application>pg_test_timing</application> tool to
+        measure the overhead of timing on your system.
+        I/O timing information is displayed in
+        <link linkend="monitoring-pg-stat-io-view">
+        <structname>pg_stat_io</structname></link> for the
+        <varname>object</varname> <literal>wal</literal> and in the output of
+        the <link linkend="pg-stat-get-backend-io">
+        <function>pg_stat_get_backend_io()</function></link> function.
+        Only superusers and users with the appropriate <literal>SET</literal>
+        privilege can change this setting.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-track-functions" xreflabel="track_functions">
       <term><varname>track_functions</varname> (<type>enum</type>)
       <indexterm>
diff --git doc/src/sgml/monitoring.sgml doc/src/sgml/monitoring.sgml
index 3dfd059b7ee8..9178f1d34efd 100644
--- doc/src/sgml/monitoring.sgml
+++ doc/src/sgml/monitoring.sgml
@@ -183,6 +183,11 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
    of block read, write, extend, and fsync times.
   </para>
 
+  <para>
+   The parameter <xref linkend="guc-track-wal-io-timing"/> enables monitoring
+   of WAL read, write and fsync times.
+  </para>
+
   <para>
    Normally these parameters are set in <filename>postgresql.conf</filename> so
    that they apply to all server processes, but it is possible to turn
@@ -2723,7 +2728,11 @@ description | Waiting for a newly initialized WAL file to reach durable storage
        </para>
        <para>
         Time spent in read operations in milliseconds (if
-        <xref linkend="guc-track-io-timing"/> is enabled, otherwise zero)
+        <xref linkend="guc-track-io-timing"/> is enabled and
+        <varname>object</varname> is not <literal>wal</literal>,
+        or if <xref linkend="guc-track-wal-io-timing"/> is enabled
+        and <varname>object</varname> is <literal>wal</literal>,
+        otherwise zero)
        </para>
       </entry>
      </row>
@@ -2757,7 +2766,11 @@ description | Waiting for a newly initialized WAL file to reach durable storage
        </para>
        <para>
         Time spent in write operations in milliseconds (if
-        <xref linkend="guc-track-io-timing"/> is enabled, otherwise zero)
+        <xref linkend="guc-track-io-timing"/> is enabled and
+        <varname>object</varname> is not <literal>wal</literal>,
+        or if <xref linkend="guc-track-wal-io-timing"/> is enabled
+        and <varname>object</varname> is <literal>wal</literal>,
+        otherwise zero)
        </para>
       </entry>
      </row>
@@ -2816,8 +2829,12 @@ description | Waiting for a newly initialized WAL file to reach durable storage
         <structfield>extend_time</structfield> <type>double precision</type>
        </para>
        <para>
-        Time spent in extend operations in milliseconds (if
-        <xref linkend="guc-track-io-timing"/> is enabled, otherwise zero)
+        Time spent in extend operations in milliseconds. (if
+        <xref linkend="guc-track-io-timing"/> is enabled and
+        <varname>object</varname> is not <literal>wal</literal>,
+        or if <xref linkend="guc-track-wal-io-timing"/> is enabled
+        and <varname>object</varname> is <literal>wal</literal>,
+        otherwise zero)
        </para>
       </entry>
      </row>
@@ -2887,7 +2904,11 @@ description | Waiting for a newly initialized WAL file to reach durable storage
        </para>
        <para>
         Time spent in fsync operations in milliseconds (if
-        <xref linkend="guc-track-io-timing"/> is enabled, otherwise zero)
+        <xref linkend="guc-track-io-timing"/> is enabled and
+        <varname>object</varname> is not <literal>wal</literal>,
+        or if <xref linkend="guc-track-wal-io-timing"/> is enabled
+        and <varname>object</varname> is <literal>wal</literal>,
+        otherwise zero)
        </para>
       </entry>
      </row>
diff --git doc/src/sgml/wal.sgml doc/src/sgml/wal.sgml
index 4fc09761115e..f3b86b26be90 100644
--- doc/src/sgml/wal.sgml
+++ doc/src/sgml/wal.sgml
@@ -808,7 +808,7 @@
   <para>
    There are two internal functions to write WAL data to disk:
    <function>XLogWrite</function> and <function>issue_xlog_fsync</function>.
-   When <xref linkend="guc-track-io-timing"/> is enabled, the total
+   When <xref linkend="guc-track-wal-io-timing"/> is enabled, the total
    amounts of time <function>XLogWrite</function> writes and
    <function>issue_xlog_fsync</function> syncs WAL data to disk are counted as
    <varname>write_time</varname> and <varname>fsync_time</varname> in
@@ -828,7 +828,7 @@
    <literal>fsync</literal>, or <literal>fsync_writethrough</literal>,
    the write operation moves WAL buffers to kernel cache and
    <function>issue_xlog_fsync</function> syncs them to disk. Regardless
-   of the setting of <varname>track_io_timing</varname>, the number
+   of the setting of <varname>track_wal_io_timing</varname>, the number
    of times <function>XLogWrite</function> writes and
    <function>issue_xlog_fsync</function> syncs WAL data to disk are also
    counted as <varname>writes</varname> and <varname>fsyncs</varname>
-- 
2.47.2

From 196f84b8bd8f817b6e21e65de90464d32a27b286 Mon Sep 17 00:00:00 2001
From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Date: Mon, 24 Feb 2025 11:29:35 +0000
Subject: [PATCH v2] re-introduce track_wal_io_timing

a051e71e28a added the "timing tracking" in the WAL code path with "only"
track_io_timing enabled (and track_wal_io_timing still false). Then it made
sense for 2421e9a51d2 to get rid of the track_wal_io_timing GUC.

Concerns have been raised about the fact that a051e71e28a added the "timing tracking"
in the WAL code path with "only" track_io_timing enabled. So this commit re-introduces
the track_wal_io_timing GUC and ensure that WAL timing is tracked in pg_stat_io
only if track_io_timing and track_wal_io_timing are both enabled.
---
 src/include/access/xlog.h                     |  1 +
 src/include/pgstat.h                          |  2 +-
 src/backend/access/transam/xlog.c             |  9 +++---
 src/backend/access/transam/xlogreader.c       |  2 +-
 src/backend/access/transam/xlogrecovery.c     |  2 +-
 src/backend/storage/buffer/bufmgr.c           | 10 +++---
 src/backend/storage/buffer/localbuf.c         |  4 +--
 src/backend/storage/smgr/md.c                 |  4 +--
 src/backend/utils/activity/pgstat_backend.c   |  3 +-
 src/backend/utils/activity/pgstat_io.c        |  9 +++---
 src/backend/utils/misc/guc_tables.c           |  9 ++++++
 src/backend/utils/misc/postgresql.conf.sample |  1 +
 doc/src/sgml/config.sgml                      | 25 +++++++++++++++
 doc/src/sgml/monitoring.sgml                  | 31 ++++++++++++++++---
 doc/src/sgml/wal.sgml                         |  4 +--
 15 files changed, 88 insertions(+), 28 deletions(-)

diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index 0a50d160bba8..d313099c027f 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -54,6 +54,7 @@ extern PGDLLIMPORT char *wal_consistency_checking_string;
 extern PGDLLIMPORT bool log_checkpoints;
 extern PGDLLIMPORT int CommitDelay;
 extern PGDLLIMPORT int CommitSiblings;
+extern PGDLLIMPORT bool track_wal_io_timing;
 extern PGDLLIMPORT int wal_decode_buffer_size;
 
 extern PGDLLIMPORT int CheckPointSegments;
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index fc651d03cf97..e64c527265b9 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -564,7 +564,7 @@ extern bool pgstat_bktype_io_stats_valid(PgStat_BktypeIO *backend_io,
 										 BackendType bktype);
 extern void pgstat_count_io_op(IOObject io_object, IOContext io_context,
 							   IOOp io_op, uint32 cnt, uint64 bytes);
-extern instr_time pgstat_prepare_io_time(void);
+extern instr_time pgstat_prepare_io_time(bool track_io_guc);
 extern void pgstat_count_io_op_time(IOObject io_object, IOContext io_context,
 									IOOp io_op, instr_time start_time,
 									uint32 cnt, uint64 bytes);
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 919314f82587..799fc739e18c 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -134,6 +134,7 @@ int			CommitSiblings = 5; /* # concurrent xacts needed to sleep */
 int			wal_retrieve_retry_interval = 5000;
 int			max_slot_wal_keep_size_mb = -1;
 int			wal_decode_buffer_size = 512 * 1024;
+bool		track_wal_io_timing = false;
 
 #ifdef WAL_DEBUG
 bool		XLOG_DEBUG = false;
@@ -2437,7 +2438,7 @@ XLogWrite(XLogwrtRqst WriteRqst, TimeLineID tli, bool flexible)
 				/*
 				 * Measure I/O timing to write WAL data, for pg_stat_io.
 				 */
-				start = pgstat_prepare_io_time();
+				start = pgstat_prepare_io_time(track_wal_io_timing);
 
 				pgstat_report_wait_start(WAIT_EVENT_WAL_WRITE);
 				written = pg_pwrite(openLogFile, from, nleft, startoffset);
@@ -3248,7 +3249,7 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
 				 errmsg("could not create file \"%s\": %m", tmppath)));
 
 	/* Measure I/O timing when initializing segment */
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_wal_io_timing);
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_WRITE);
 	save_errno = 0;
@@ -3310,7 +3311,7 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
 	}
 
 	/* Measure I/O timing when flushing segment */
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_wal_io_timing);
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_SYNC);
 	if (pg_fsync(fd) != 0)
@@ -8744,7 +8745,7 @@ issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
 	/*
 	 * Measure I/O timing to sync the WAL file for pg_stat_io.
 	 */
-	start = pgstat_prepare_io_time();
+	start = pgstat_prepare_io_time(track_wal_io_timing);
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_SYNC);
 	switch (wal_sync_method)
diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
index 995e4f7c26fd..5483d4f0dd2b 100644
--- a/src/backend/access/transam/xlogreader.c
+++ b/src/backend/access/transam/xlogreader.c
@@ -1557,7 +1557,7 @@ WALRead(XLogReaderState *state,
 
 #ifndef FRONTEND
 		/* Measure I/O timing when reading segment */
-		io_start = pgstat_prepare_io_time();
+		io_start = pgstat_prepare_io_time(track_wal_io_timing);
 
 		pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
 #endif
diff --git a/src/backend/access/transam/xlogrecovery.c b/src/backend/access/transam/xlogrecovery.c
index 915cb330295c..c5475aaa97a1 100644
--- a/src/backend/access/transam/xlogrecovery.c
+++ b/src/backend/access/transam/xlogrecovery.c
@@ -3401,7 +3401,7 @@ retry:
 	readOff = targetPageOff;
 
 	/* Measure I/O timing when reading segment */
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_wal_io_timing);
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
 	r = pg_pread(readFile, readBuf, XLOG_BLCKSZ, (off_t) readOff);
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index d3216ef6ba75..75cfc2b6fe96 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -1509,7 +1509,7 @@ WaitReadBuffers(ReadBuffersOperation *operation)
 			io_pages[io_buffers_len++] = BufferGetBlock(buffers[i]);
 		}
 
-		io_start = pgstat_prepare_io_time();
+		io_start = pgstat_prepare_io_time(track_io_timing);
 		smgrreadv(operation->smgr, forknum, io_first_block, io_pages, io_buffers_len);
 		pgstat_count_io_op_time(io_object, io_context, IOOP_READ, io_start,
 								1, io_buffers_len * BLCKSZ);
@@ -2401,7 +2401,7 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
 		}
 	}
 
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	/*
 	 * Note: if smgrzeroextend fails, we will end up with buffers that are
@@ -3858,7 +3858,7 @@ FlushBuffer(BufferDesc *buf, SMgrRelation reln, IOObject io_object,
 	 */
 	bufToWrite = PageSetChecksumCopy((Page) bufBlock, buf->tag.blockNum);
 
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	/*
 	 * bufToWrite is either the shared buffer or a copy, as appropriate.
@@ -4460,7 +4460,7 @@ FlushRelationBuffers(Relation rel)
 
 				PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);
 
-				io_start = pgstat_prepare_io_time();
+				io_start = pgstat_prepare_io_time(track_io_timing);
 
 				smgrwrite(srel,
 						  BufTagGetForkNum(&bufHdr->tag),
@@ -5917,7 +5917,7 @@ IssuePendingWritebacks(WritebackContext *wb_context, IOContext io_context)
 	sort_pending_writebacks(wb_context->pending_writebacks,
 							wb_context->nr_pending);
 
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	/*
 	 * Coalesce neighbouring writes, but nothing else. For that we iterate
diff --git a/src/backend/storage/buffer/localbuf.c b/src/backend/storage/buffer/localbuf.c
index 78b65fb160ad..64931efaa756 100644
--- a/src/backend/storage/buffer/localbuf.c
+++ b/src/backend/storage/buffer/localbuf.c
@@ -244,7 +244,7 @@ GetLocalVictimBuffer(void)
 
 		PageSetChecksumInplace(localpage, bufHdr->tag.blockNum);
 
-		io_start = pgstat_prepare_io_time();
+		io_start = pgstat_prepare_io_time(track_io_timing);
 
 		/* And write... */
 		smgrwrite(oreln,
@@ -414,7 +414,7 @@ ExtendBufferedRelLocal(BufferManagerRelation bmr,
 		}
 	}
 
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	/* actually extend relation */
 	smgrzeroextend(bmr.smgr, fork, first_block, extend_by, false);
diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
index 298754d1b64a..7bf0b45e2c34 100644
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -1381,7 +1381,7 @@ register_dirty_segment(SMgrRelation reln, ForkNumber forknum, MdfdVec *seg)
 		ereport(DEBUG1,
 				(errmsg_internal("could not forward fsync request because request queue is full")));
 
-		io_start = pgstat_prepare_io_time();
+		io_start = pgstat_prepare_io_time(track_io_timing);
 
 		if (FileSync(seg->mdfd_vfd, WAIT_EVENT_DATA_FILE_SYNC) < 0)
 			ereport(data_sync_elevel(ERROR),
@@ -1786,7 +1786,7 @@ mdsyncfiletag(const FileTag *ftag, char *path)
 		need_to_close = true;
 	}
 
-	io_start = pgstat_prepare_io_time();
+	io_start = pgstat_prepare_io_time(track_io_timing);
 
 	/* Sync the file. */
 	result = FileSync(file, WAIT_EVENT_DATA_FILE_SYNC);
diff --git a/src/backend/utils/activity/pgstat_backend.c b/src/backend/utils/activity/pgstat_backend.c
index 4a667e7019cc..338da73a9a91 100644
--- a/src/backend/utils/activity/pgstat_backend.c
+++ b/src/backend/utils/activity/pgstat_backend.c
@@ -24,6 +24,7 @@
 
 #include "postgres.h"
 
+#include "access/xlog.h"
 #include "storage/bufmgr.h"
 #include "utils/memutils.h"
 #include "utils/pgstat_internal.h"
@@ -43,7 +44,7 @@ void
 pgstat_count_backend_io_op_time(IOObject io_object, IOContext io_context,
 								IOOp io_op, instr_time io_time)
 {
-	Assert(track_io_timing);
+	Assert(track_io_timing || track_wal_io_timing);
 
 	if (!pgstat_tracks_backend_bktype(MyBackendType))
 		return;
diff --git a/src/backend/utils/activity/pgstat_io.c b/src/backend/utils/activity/pgstat_io.c
index e7362b52a37b..edb489f3a864 100644
--- a/src/backend/utils/activity/pgstat_io.c
+++ b/src/backend/utils/activity/pgstat_io.c
@@ -83,14 +83,15 @@ pgstat_count_io_op(IOObject io_object, IOContext io_context, IOOp io_op,
 }
 
 /*
- * Initialize the internal timing for an IO operation.
+ * Initialize the internal timing for an IO operation, depending on an
+ * IO timing GUC.
  */
 instr_time
-pgstat_prepare_io_time(void)
+pgstat_prepare_io_time(bool track_io_guc)
 {
 	instr_time	io_start;
 
-	if (track_io_timing)
+	if (track_io_guc)
 		INSTR_TIME_SET_CURRENT(io_start);
 	else
 	{
@@ -119,7 +120,7 @@ void
 pgstat_count_io_op_time(IOObject io_object, IOContext io_context, IOOp io_op,
 						instr_time start_time, uint32 cnt, uint64 bytes)
 {
-	if (track_io_timing)
+	if (!INSTR_TIME_IS_ZERO(start_time))
 	{
 		instr_time	io_time;
 
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 690bf96ef030..ad25cbb39c55 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -1501,6 +1501,15 @@ struct config_bool ConfigureNamesBool[] =
 		false,
 		NULL, NULL, NULL
 	},
+	{
+		{"track_wal_io_timing", PGC_SUSET, STATS_CUMULATIVE,
+			gettext_noop("Collects timing statistics for WAL I/O activity."),
+			NULL
+		},
+		&track_wal_io_timing,
+		false,
+		NULL, NULL, NULL
+	},
 
 	{
 		{"update_process_title", PGC_SUSET, PROCESS_TITLE,
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index e771d87da1fb..5362ff805195 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -641,6 +641,7 @@
 #track_counts = on
 #track_cost_delay_timing = off
 #track_io_timing = off
+#track_wal_io_timing = off
 #track_functions = none			# none, pl, all
 #stats_fetch_consistency = cache	# cache, none, snapshot
 
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index a83545761085..6186648ccaf5 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -8393,6 +8393,31 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-track-wal-io-timing" xreflabel="track_wal_io_timing">
+      <term><varname>track_wal_io_timing</varname> (<type>boolean</type>)
+      <indexterm>
+       <primary><varname>track_wal_io_timing</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Enables timing of WAL I/O calls. This parameter is off by default,
+        as it will repeatedly query the operating system for the current time,
+        which may cause significant overhead on some platforms.
+        You can use the <application>pg_test_timing</application> tool to
+        measure the overhead of timing on your system.
+        I/O timing information is displayed in
+        <link linkend="monitoring-pg-stat-io-view">
+        <structname>pg_stat_io</structname></link> for the
+        <varname>object</varname> <literal>wal</literal> and in the output of
+        the <link linkend="pg-stat-get-backend-io">
+        <function>pg_stat_get_backend_io()</function></link> function.
+        Only superusers and users with the appropriate <literal>SET</literal>
+        privilege can change this setting.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-track-functions" xreflabel="track_functions">
       <term><varname>track_functions</varname> (<type>enum</type>)
       <indexterm>
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 3dfd059b7ee8..9178f1d34efd 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -183,6 +183,11 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
    of block read, write, extend, and fsync times.
   </para>
 
+  <para>
+   The parameter <xref linkend="guc-track-wal-io-timing"/> enables monitoring
+   of WAL read, write and fsync times.
+  </para>
+
   <para>
    Normally these parameters are set in <filename>postgresql.conf</filename> so
    that they apply to all server processes, but it is possible to turn
@@ -2723,7 +2728,11 @@ description | Waiting for a newly initialized WAL file to reach durable storage
        </para>
        <para>
         Time spent in read operations in milliseconds (if
-        <xref linkend="guc-track-io-timing"/> is enabled, otherwise zero)
+        <xref linkend="guc-track-io-timing"/> is enabled and
+        <varname>object</varname> is not <literal>wal</literal>,
+        or if <xref linkend="guc-track-wal-io-timing"/> is enabled
+        and <varname>object</varname> is <literal>wal</literal>,
+        otherwise zero)
        </para>
       </entry>
      </row>
@@ -2757,7 +2766,11 @@ description | Waiting for a newly initialized WAL file to reach durable storage
        </para>
        <para>
         Time spent in write operations in milliseconds (if
-        <xref linkend="guc-track-io-timing"/> is enabled, otherwise zero)
+        <xref linkend="guc-track-io-timing"/> is enabled and
+        <varname>object</varname> is not <literal>wal</literal>,
+        or if <xref linkend="guc-track-wal-io-timing"/> is enabled
+        and <varname>object</varname> is <literal>wal</literal>,
+        otherwise zero)
        </para>
       </entry>
      </row>
@@ -2816,8 +2829,12 @@ description | Waiting for a newly initialized WAL file to reach durable storage
         <structfield>extend_time</structfield> <type>double precision</type>
        </para>
        <para>
-        Time spent in extend operations in milliseconds (if
-        <xref linkend="guc-track-io-timing"/> is enabled, otherwise zero)
+        Time spent in extend operations in milliseconds. (if
+        <xref linkend="guc-track-io-timing"/> is enabled and
+        <varname>object</varname> is not <literal>wal</literal>,
+        or if <xref linkend="guc-track-wal-io-timing"/> is enabled
+        and <varname>object</varname> is <literal>wal</literal>,
+        otherwise zero)
        </para>
       </entry>
      </row>
@@ -2887,7 +2904,11 @@ description | Waiting for a newly initialized WAL file to reach durable storage
        </para>
        <para>
         Time spent in fsync operations in milliseconds (if
-        <xref linkend="guc-track-io-timing"/> is enabled, otherwise zero)
+        <xref linkend="guc-track-io-timing"/> is enabled and
+        <varname>object</varname> is not <literal>wal</literal>,
+        or if <xref linkend="guc-track-wal-io-timing"/> is enabled
+        and <varname>object</varname> is <literal>wal</literal>,
+        otherwise zero)
        </para>
       </entry>
      </row>
diff --git a/doc/src/sgml/wal.sgml b/doc/src/sgml/wal.sgml
index 4fc09761115e..f3b86b26be90 100644
--- a/doc/src/sgml/wal.sgml
+++ b/doc/src/sgml/wal.sgml
@@ -808,7 +808,7 @@
   <para>
    There are two internal functions to write WAL data to disk:
    <function>XLogWrite</function> and <function>issue_xlog_fsync</function>.
-   When <xref linkend="guc-track-io-timing"/> is enabled, the total
+   When <xref linkend="guc-track-wal-io-timing"/> is enabled, the total
    amounts of time <function>XLogWrite</function> writes and
    <function>issue_xlog_fsync</function> syncs WAL data to disk are counted as
    <varname>write_time</varname> and <varname>fsync_time</varname> in
@@ -828,7 +828,7 @@
    <literal>fsync</literal>, or <literal>fsync_writethrough</literal>,
    the write operation moves WAL buffers to kernel cache and
    <function>issue_xlog_fsync</function> syncs them to disk. Regardless
-   of the setting of <varname>track_io_timing</varname>, the number
+   of the setting of <varname>track_wal_io_timing</varname>, the number
    of times <function>XLogWrite</function> writes and
    <function>issue_xlog_fsync</function> syncs WAL data to disk are also
    counted as <varname>writes</varname> and <varname>fsyncs</varname>
-- 
2.47.2

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 6186648ccaf..e55700f35b8 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -8378,9 +8378,11 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
         displayed in <link linkend="monitoring-pg-stat-database-view">
         <structname>pg_stat_database</structname></link>,
         <link linkend="monitoring-pg-stat-io-view">
-        <structname>pg_stat_io</structname></link>, in the output of the
+        <structname>pg_stat_io</structname></link> (if <varname>object</varname>
+        is not <literal>wal</literal>), in the output of the
         <link linkend="pg-stat-get-backend-io">
-        <function>pg_stat_get_backend_io()</function></link> function, in the
+        <function>pg_stat_get_backend_io()</function></link> function (if
+        <varname>object</varname> is not <literal>wal</literal>), in the
         output of <xref linkend="sql-explain"/> when the <literal>BUFFERS</literal>
         option is used, in the output of <xref linkend="sql-vacuum"/> when
         the <literal>VERBOSE</literal> option is used, by autovacuum
@@ -8411,7 +8413,8 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
         <structname>pg_stat_io</structname></link> for the
         <varname>object</varname> <literal>wal</literal> and in the output of
         the <link linkend="pg-stat-get-backend-io">
-        <function>pg_stat_get_backend_io()</function></link> function.
+        <function>pg_stat_get_backend_io()</function></link> function for the
+        <varname>object</varname> <literal>wal</literal>.
         Only superusers and users with the appropriate <literal>SET</literal>
         privilege can change this setting.
        </para>