Add data for WAL in pg_stat_io and backend statistics

This commit adds WAL IO stats to both pg_stat_io view and per-backend IO
statistics (pg_stat_get_backend_io()).  This change is possible since
f92c854cf4, as WAL IO is not counted in blocks in some code paths
where its stats data is measured (like WAL read in xlogreader.c).

IOContext gains IOCONTEXT_INIT and IOObject IOOBJECT_WAL, with the
following combinations allowed:
- IOOBJECT_WAL/IOCONTEXT_NORMAL is used to track I/O operations done on
already-created WAL segments.
- IOOBJECT_WAL/IOCONTEXT_INIT is used for tracking I/O operations done
when initializing WAL segments.

The core changes are done in pg_stat_io.c, backend statistics inherit
them.  Backend statistics and pg_stat_io are now available for the WAL
writer, the WAL receiver and the WAL summarizer processes.

I/O timing data is controlled by the GUC track_io_timing, like the
existing data of pg_stat_io for consistency.  The timings related to
IOOBJECT_WAL show up if the GUC is enabled (disabled by default).

Bump pgstats file version, due to the additions in IOObject and
IOContext, impacting the amount of data written for the fixed-numbered
IO stats kind in the pgstats file.

Author: Nazir Bilal Yavuz
Reviewed-by: Bertrand Drouvot, Nitin Jadhav, Amit Kapila, Michael
Paquier, Melanie Plageman, Bharath Rupireddy
Discussion: https://postgr.es/m/CAN55FZ3AiQ+ZMxUuXnBpd0Rrh1YhwJ5FudkHg=JU0P+-W8T4Vg@mail.gmail.com

doc/src/sgml/monitoring.sgml

@@ -2581,9 +2581,10 @@ description | Waiting for a newly initialized WAL file to reach durable storage
   </para>
 
   <para>
-   Currently, I/O on relations (e.g. tables, indexes) is tracked. However,
+   Currently, I/O on relations (e.g. tables, indexes) and WAL activity are
-   relation I/O which bypasses shared buffers (e.g. when moving a table from one
+   tracked. However, relation I/O which bypasses shared buffers
-   tablespace to another) is currently not tracked.
+   (e.g. when moving a table from one tablespace to another) is currently
+   not tracked.
   </para>
 
   <table id="pg-stat-io-view" xreflabel="pg_stat_io">
@@ -2636,6 +2637,11 @@ description | Waiting for a newly initialized WAL file to reach durable storage
           <literal>temp relation</literal>: Temporary relations.
          </para>
         </listitem>
+        <listitem>
+         <para>
+          <literal>wal</literal>: Write Ahead Logs.
+         </para>
+        </listitem>
        </itemizedlist>
        </para>
       </entry>
@@ -2660,6 +2666,13 @@ description | Waiting for a newly initialized WAL file to reach durable storage
           <literal>normal</literal>.
          </para>
         </listitem>
+        <listitem>
+         <para>
+          <literal>init</literal>: I/O operations performed while creating the
+          WAL segments are tracked in <varname>context</varname>
+          <literal>init</literal>.
+         </para>
+        </listitem>
         <listitem>
          <para>
           <literal>vacuum</literal>: I/O operations performed outside of shared

src/backend/access/transam/xlog.c

@@ -2435,16 +2435,19 @@ XLogWrite(XLogwrtRqst WriteRqst, TimeLineID tli, bool flexible)
 			{
 				errno = 0;
 
-				/* Measure I/O timing to write WAL data */
+				/*
-				if (track_wal_io_timing)
+				 * Measure I/O timing to write WAL data, for pg_stat_io and/or
-					INSTR_TIME_SET_CURRENT(start);
+				 * pg_stat_wal.
-				else
+				 */
-					INSTR_TIME_SET_ZERO(start);
+				start = pgstat_prepare_io_time(track_io_timing || track_wal_io_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);
+
 				/*
 				 * Increment the I/O timing and the number of times WAL data
 				 * were written out to disk.
@@ -3216,6 +3219,7 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
 	int			fd;
 	int			save_errno;
 	int			open_flags = O_RDWR | O_CREAT | O_EXCL | PG_BINARY;
+	instr_time	io_start;
 
 	Assert(logtli != 0);
 
@@ -3259,6 +3263,9 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
 				(errcode_for_file_access(),
 				 errmsg("could not create file \"%s\": %m", tmppath)));
 
+	/* Measure I/O timing when initializing segment */
+	io_start = pgstat_prepare_io_time(track_io_timing);
+
 	pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_WRITE);
 	save_errno = 0;
 	if (wal_init_zero)
@@ -3294,6 +3301,14 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
 	}
 	pgstat_report_wait_end();
 
+	/*
+	 * A full segment worth of data is written when using wal_init_zero. One
+	 * byte is written when not using it.
+	 */
+	pgstat_count_io_op_time(IOOBJECT_WAL, IOCONTEXT_INIT, IOOP_WRITE,
+							io_start, 1,
+							wal_init_zero ? wal_segment_size : 1);
+
 	if (save_errno)
 	{
 		/*
@@ -3310,6 +3325,9 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
 				 errmsg("could not write to file \"%s\": %m", tmppath)));
 	}
 
+	/* Measure I/O timing when flushing segment */
+	io_start = pgstat_prepare_io_time(track_io_timing);
+
 	pgstat_report_wait_start(WAIT_EVENT_WAL_INIT_SYNC);
 	if (pg_fsync(fd) != 0)
 	{
@@ -3322,6 +3340,9 @@ XLogFileInitInternal(XLogSegNo logsegno, TimeLineID logtli,
 	}
 	pgstat_report_wait_end();
 
+	pgstat_count_io_op_time(IOOBJECT_WAL, IOCONTEXT_INIT,
+							IOOP_FSYNC, io_start, 1, 0);
+
 	if (close(fd) != 0)
 		ereport(ERROR,
 				(errcode_for_file_access(),
@@ -8696,11 +8717,11 @@ issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
 		wal_sync_method == WAL_SYNC_METHOD_OPEN_DSYNC)
 		return;
 
-	/* Measure I/O timing to sync the WAL file */
+	/*
-	if (track_wal_io_timing)
+	 * Measure I/O timing to sync the WAL file for pg_stat_io and/or
-		INSTR_TIME_SET_CURRENT(start);
+	 * pg_stat_wal.
-	else
+	 */
-		INSTR_TIME_SET_ZERO(start);
+	start = pgstat_prepare_io_time(track_io_timing || track_wal_io_timing);
 
 	pgstat_report_wait_start(WAIT_EVENT_WAL_SYNC);
 	switch (wal_sync_method)
@@ -8757,6 +8778,9 @@ issue_xlog_fsync(int fd, XLogSegNo segno, TimeLineID tli)
 		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++;
 }
 

src/backend/access/transam/xlogreader.c

@@ -35,6 +35,7 @@
 
 #ifndef FRONTEND
 #include "pgstat.h"
+#include "storage/bufmgr.h"
 #else
 #include "common/logging.h"
 #endif
@@ -1507,6 +1508,9 @@ WALRead(XLogReaderState *state,
 	char	   *p;
 	XLogRecPtr	recptr;
 	Size		nbytes;
+#ifndef FRONTEND
+	instr_time	io_start;
+#endif
 
 	p = buf;
 	recptr = startptr;
@@ -1552,6 +1556,9 @@ WALRead(XLogReaderState *state,
 			segbytes = nbytes;
 
 #ifndef FRONTEND
+		/* Measure I/O timing when reading segment */
+		io_start = pgstat_prepare_io_time(track_io_timing);
+
 		pgstat_report_wait_start(WAIT_EVENT_WAL_READ);
 #endif
 
@@ -1561,6 +1568,9 @@ WALRead(XLogReaderState *state,
 
 #ifndef FRONTEND
 		pgstat_report_wait_end();
+
+		pgstat_count_io_op_time(IOOBJECT_WAL, IOCONTEXT_NORMAL, IOOP_READ,
+								io_start, 1, readbytes);
 #endif
 
 		if (readbytes <= 0)

src/backend/access/transam/xlogrecovery.c

@@ -60,6 +60,7 @@
 #include "utils/datetime.h"
 #include "utils/fmgrprotos.h"
 #include "utils/guc_hooks.h"
+#include "utils/pgstat_internal.h"
 #include "utils/pg_lsn.h"
 #include "utils/ps_status.h"
 #include "utils/pg_rusage.h"
@@ -3306,6 +3307,7 @@ XLogPageRead(XLogReaderState *xlogreader, XLogRecPtr targetPagePtr, int reqLen,
 	uint32		targetPageOff;
 	XLogSegNo	targetSegNo PG_USED_FOR_ASSERTS_ONLY;
 	int			r;
+	instr_time	io_start;
 
 	XLByteToSeg(targetPagePtr, targetSegNo, wal_segment_size);
 	targetPageOff = XLogSegmentOffset(targetPagePtr, wal_segment_size);
@@ -3398,6 +3400,9 @@ retry:
 	/* Read the requested page */
 	readOff = targetPageOff;
 
+	/* Measure I/O timing when reading segment */
+	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);
 	if (r != XLOG_BLCKSZ)
@@ -3406,6 +3411,10 @@ retry:
 		int			save_errno = errno;
 
 		pgstat_report_wait_end();
+
+		pgstat_count_io_op_time(IOOBJECT_WAL, IOCONTEXT_NORMAL, IOOP_READ,
+								io_start, 1, r);
+
 		XLogFileName(fname, curFileTLI, readSegNo, wal_segment_size);
 		if (r < 0)
 		{
@@ -3426,6 +3435,9 @@ retry:
 	}
 	pgstat_report_wait_end();
 
+	pgstat_count_io_op_time(IOOBJECT_WAL, IOCONTEXT_NORMAL, IOOP_READ,
+							io_start, 1, r);
+
 	Assert(targetSegNo == readSegNo);
 	Assert(targetPageOff == readOff);
 	Assert(reqLen <= readLen);

src/backend/utils/activity/pgstat_backend.c

@@ -236,9 +236,6 @@ pgstat_tracks_backend_bktype(BackendType bktype)
 		case B_DEAD_END_BACKEND:
 		case B_ARCHIVER:
 		case B_LOGGER:
-		case B_WAL_RECEIVER:
-		case B_WAL_WRITER:
-		case B_WAL_SUMMARIZER:
 		case B_BG_WRITER:
 		case B_CHECKPOINTER:
 		case B_STARTUP:
@@ -249,7 +246,10 @@ pgstat_tracks_backend_bktype(BackendType bktype)
 		case B_BG_WORKER:
 		case B_STANDALONE_BACKEND:
 		case B_SLOTSYNC_WORKER:
+		case B_WAL_RECEIVER:
 		case B_WAL_SENDER:
+		case B_WAL_SUMMARIZER:
+		case B_WAL_WRITER:
 			return true;
 	}
 

src/backend/utils/activity/pgstat_io.c

@@ -127,6 +127,8 @@ pgstat_count_io_op_time(IOObject io_object, IOContext io_context, IOOp io_op,
 		INSTR_TIME_SET_CURRENT(io_time);
 		INSTR_TIME_SUBTRACT(io_time, start_time);
 
+		if (io_object != IOOBJECT_WAL)
+		{
 			if (io_op == IOOP_WRITE || io_op == IOOP_EXTEND)
 			{
 				pgstat_count_buffer_write_time(INSTR_TIME_GET_MICROSEC(io_time));
@@ -143,6 +145,7 @@ pgstat_count_io_op_time(IOObject io_object, IOContext io_context, IOOp io_op,
 				else if (io_object == IOOBJECT_TEMP_RELATION)
 					INSTR_TIME_ADD(pgBufferUsage.local_blk_read_time, io_time);
 			}
+		}
 
 		INSTR_TIME_ADD(PendingIOStats.pending_times[io_object][io_context][io_op],
 					   io_time);
@@ -249,6 +252,8 @@ pgstat_get_io_context_name(IOContext io_context)
 			return "bulkread";
 		case IOCONTEXT_BULKWRITE:
 			return "bulkwrite";
+		case IOCONTEXT_INIT:
+			return "init";
 		case IOCONTEXT_NORMAL:
 			return "normal";
 		case IOCONTEXT_VACUUM:
@@ -268,6 +273,8 @@ pgstat_get_io_object_name(IOObject io_object)
 			return "relation";
 		case IOOBJECT_TEMP_RELATION:
 			return "temp relation";
+		case IOOBJECT_WAL:
+			return "wal";
 	}
 
 	elog(ERROR, "unrecognized IOObject value: %d", io_object);
@@ -340,8 +347,6 @@ pgstat_io_snapshot_cb(void)
 * - Syslogger because it is not connected to shared memory
 * - Archiver because most relevant archiving IO is delegated to a
 *   specialized command or module
-* - WAL Receiver, WAL Writer, and WAL Summarizer IO are not tracked in
-*   pg_stat_io for now
 *
 * Function returns true if BackendType participates in the cumulative stats
 * subsystem for IO and false if it does not.
@@ -362,9 +367,6 @@ pgstat_tracks_io_bktype(BackendType bktype)
 		case B_DEAD_END_BACKEND:
 		case B_ARCHIVER:
 		case B_LOGGER:
-		case B_WAL_RECEIVER:
-		case B_WAL_WRITER:
-		case B_WAL_SUMMARIZER:
 			return false;
 
 		case B_AUTOVAC_LAUNCHER:
@@ -376,7 +378,10 @@ pgstat_tracks_io_bktype(BackendType bktype)
 		case B_SLOTSYNC_WORKER:
 		case B_STANDALONE_BACKEND:
 		case B_STARTUP:
+		case B_WAL_RECEIVER:
 		case B_WAL_SENDER:
+		case B_WAL_SUMMARIZER:
+		case B_WAL_WRITER:
 			return true;
 	}
 
@@ -402,6 +407,15 @@ pgstat_tracks_io_object(BackendType bktype, IOObject io_object,
 	if (!pgstat_tracks_io_bktype(bktype))
 		return false;
 
+	/*
+	 * Currently, IO on IOOBJECT_WAL objects can only occur in the
+	 * IOCONTEXT_NORMAL and IOCONTEXT_INIT IOContexts.
+	 */
+	if (io_object == IOOBJECT_WAL &&
+		(io_context != IOCONTEXT_NORMAL &&
+		 io_context != IOCONTEXT_INIT))
+		return false;
+
 	/*
 	 * Currently, IO on temporary relations can only occur in the
 	 * IOCONTEXT_NORMAL IOContext.
@@ -468,14 +482,28 @@ pgstat_tracks_io_op(BackendType bktype, IOObject io_object,
 	/*
 	 * Some BackendTypes will not do certain IOOps.
 	 */
-	if ((bktype == B_BG_WRITER || bktype == B_CHECKPOINTER) &&
+	if (bktype == B_BG_WRITER &&
 		(io_op == IOOP_READ || io_op == IOOP_EVICT || io_op == IOOP_HIT))
 		return false;
 
+	if (bktype == B_CHECKPOINTER &&
+		((io_object != IOOBJECT_WAL && io_op == IOOP_READ) ||
+		 (io_op == IOOP_EVICT || io_op == IOOP_HIT)))
+		return false;
+
 	if ((bktype == B_AUTOVAC_LAUNCHER || bktype == B_BG_WRITER ||
 		 bktype == B_CHECKPOINTER) && io_op == IOOP_EXTEND)
 		return false;
 
+	/*
+	 * Some BackendTypes do not perform reads with IOOBJECT_WAL.
+	 */
+	if (io_object == IOOBJECT_WAL && io_op == IOOP_READ &&
+		(bktype == B_WAL_RECEIVER || bktype == B_BG_WRITER ||
+		 bktype == B_AUTOVAC_WORKER || bktype == B_AUTOVAC_WORKER ||
+		 bktype == B_WAL_WRITER))
+		return false;
+
 	/*
 	 * Temporary tables are not logged and thus do not require fsync'ing.
 	 * Writeback is not requested for temporary tables.
@@ -500,6 +528,17 @@ pgstat_tracks_io_op(BackendType bktype, IOObject io_object,
 	if (!strategy_io_context && io_op == IOOP_REUSE)
 		return false;
 
+	/*
+	 * IOOBJECT_WAL IOObject will not do certain IOOps depending on IOContext.
+	 */
+	if (io_object == IOOBJECT_WAL && io_context == IOCONTEXT_INIT &&
+		!(io_op == IOOP_WRITE || io_op == IOOP_FSYNC))
+		return false;
+
+	if (io_object == IOOBJECT_WAL && io_context == IOCONTEXT_NORMAL &&
+		!(io_op == IOOP_WRITE || io_op == IOOP_READ || io_op == IOOP_FSYNC))
+		return false;
+
 	/*
 	 * IOOP_FSYNC IOOps done by a backend using a BufferAccessStrategy are
 	 * counted in the IOCONTEXT_NORMAL IOContext. See comment in

src/include/pgstat.h

@@ -212,7 +212,7 @@ typedef struct PgStat_TableXactStatus
  * ------------------------------------------------------------
  */
 
-#define PGSTAT_FILE_FORMAT_ID	0x01A5BCB2
+#define PGSTAT_FILE_FORMAT_ID	0x01A5BCB3
 
 typedef struct PgStat_ArchiverStats
 {
@@ -274,14 +274,16 @@ typedef enum IOObject
 {
 	IOOBJECT_RELATION,
 	IOOBJECT_TEMP_RELATION,
+	IOOBJECT_WAL,
 } IOObject;
 
-#define IOOBJECT_NUM_TYPES (IOOBJECT_TEMP_RELATION + 1)
+#define IOOBJECT_NUM_TYPES (IOOBJECT_WAL + 1)
 
 typedef enum IOContext
 {
 	IOCONTEXT_BULKREAD,
 	IOCONTEXT_BULKWRITE,
+	IOCONTEXT_INIT,
 	IOCONTEXT_NORMAL,
 	IOCONTEXT_VACUUM,
 } IOContext;

src/test/regress/expected/stats.out

@@ -862,6 +862,33 @@ WHERE pg_stat_get_backend_pid(beid) = pg_backend_pid();
  t
 (1 row)
 
+-- Test pg_stat_io for WAL in an init context, that should do writes
+-- and syncs.
+SELECT sum(writes) AS writes, sum(fsyncs) AS fsyncs
+  FROM pg_stat_io
+  WHERE context = 'init' AND object = 'wal' \gset io_sum_wal_init_
+SELECT :io_sum_wal_init_writes > 0;
+ ?column? 
+----------
+ t
+(1 row)
+
+SELECT current_setting('fsync') = 'off'
+  OR :io_sum_wal_init_fsyncs > 0;
+ ?column? 
+----------
+ t
+(1 row)
+
+-- Test pg_stat_io for WAL in a normal context, that should do reads as well.
+SELECT SUM(reads) > 0
+  FROM pg_stat_io
+  WHERE context = 'normal' AND object = 'wal';
+ ?column? 
+----------
+ t
+(1 row)
+
 -----
 -- Test that resetting stats works for reset timestamp
 -----
@@ -1256,6 +1283,7 @@ SELECT pg_stat_get_subscription_stats(NULL);
 -- - extends of relations using shared buffers
 -- - fsyncs done to ensure the durability of data dirtying shared buffers
 -- - shared buffer hits
+-- - WAL writes and fsyncs in IOContext IOCONTEXT_NORMAL
 -- There is no test for blocks evicted from shared buffers, because we cannot
 -- be sure of the state of shared buffers at the point the test is run.
 -- Create a regular table and insert some data to generate IOCONTEXT_NORMAL
@@ -1273,6 +1301,9 @@ SELECT sum(writes) AS writes, sum(fsyncs) AS fsyncs
 SELECT sum(writes) AS writes, sum(fsyncs) AS fsyncs
   FROM pg_stat_get_backend_io(pg_backend_pid())
   WHERE object = 'relation' \gset my_io_sum_shared_before_
+SELECT sum(writes) AS writes, sum(fsyncs) AS fsyncs
+  FROM pg_stat_io
+  WHERE context = 'normal' AND object = 'wal' \gset io_sum_wal_normal_before_
 CREATE TABLE test_io_shared(a int);
 INSERT INTO test_io_shared SELECT i FROM generate_series(1,100)i;
 SELECT pg_stat_force_next_flush();
@@ -1335,6 +1366,28 @@ SELECT current_setting('fsync') = 'off'
  t
 (1 row)
 
+SELECT sum(writes) AS writes, sum(fsyncs) AS fsyncs
+  FROM pg_stat_io
+  WHERE context = 'normal' AND object = 'wal' \gset io_sum_wal_normal_after_
+SELECT current_setting('synchronous_commit') = 'on';
+ ?column? 
+----------
+ t
+(1 row)
+
+SELECT :io_sum_wal_normal_after_writes > :io_sum_wal_normal_before_writes;
+ ?column? 
+----------
+ t
+(1 row)
+
+SELECT current_setting('fsync') = 'off'
+  OR :io_sum_wal_normal_after_fsyncs > :io_sum_wal_normal_before_fsyncs;
+ ?column? 
+----------
+ t
+(1 row)
+
 -- Change the tablespace so that the table is rewritten directly, then SELECT
 -- from it to cause it to be read back into shared buffers.
 SELECT sum(reads) AS io_sum_shared_before_reads

src/test/regress/sql/stats.sql

@@ -442,6 +442,20 @@ SELECT (current_schemas(true))[1] = ('pg_temp_' || beid::text) AS match
 FROM pg_stat_get_backend_idset() beid
 WHERE pg_stat_get_backend_pid(beid) = pg_backend_pid();
 
+-- Test pg_stat_io for WAL in an init context, that should do writes
+-- and syncs.
+SELECT sum(writes) AS writes, sum(fsyncs) AS fsyncs
+  FROM pg_stat_io
+  WHERE context = 'init' AND object = 'wal' \gset io_sum_wal_init_
+SELECT :io_sum_wal_init_writes > 0;
+SELECT current_setting('fsync') = 'off'
+  OR :io_sum_wal_init_fsyncs > 0;
+
+-- Test pg_stat_io for WAL in a normal context, that should do reads as well.
+SELECT SUM(reads) > 0
+  FROM pg_stat_io
+  WHERE context = 'normal' AND object = 'wal';
+
 -----
 -- Test that resetting stats works for reset timestamp
 -----
@@ -602,6 +616,7 @@ SELECT pg_stat_get_subscription_stats(NULL);
 -- - extends of relations using shared buffers
 -- - fsyncs done to ensure the durability of data dirtying shared buffers
 -- - shared buffer hits
+-- - WAL writes and fsyncs in IOContext IOCONTEXT_NORMAL
 
 -- There is no test for blocks evicted from shared buffers, because we cannot
 -- be sure of the state of shared buffers at the point the test is run.
@@ -621,6 +636,9 @@ SELECT sum(writes) AS writes, sum(fsyncs) AS fsyncs
 SELECT sum(writes) AS writes, sum(fsyncs) AS fsyncs
   FROM pg_stat_get_backend_io(pg_backend_pid())
   WHERE object = 'relation' \gset my_io_sum_shared_before_
+SELECT sum(writes) AS writes, sum(fsyncs) AS fsyncs
+  FROM pg_stat_io
+  WHERE context = 'normal' AND object = 'wal' \gset io_sum_wal_normal_before_
 CREATE TABLE test_io_shared(a int);
 INSERT INTO test_io_shared SELECT i FROM generate_series(1,100)i;
 SELECT pg_stat_force_next_flush();
@@ -649,6 +667,13 @@ SELECT sum(writes) AS writes, sum(fsyncs) AS fsyncs
 SELECT :my_io_sum_shared_after_writes >= :my_io_sum_shared_before_writes;
 SELECT current_setting('fsync') = 'off'
   OR :my_io_sum_shared_after_fsyncs >= :my_io_sum_shared_before_fsyncs;
+SELECT sum(writes) AS writes, sum(fsyncs) AS fsyncs
+  FROM pg_stat_io
+  WHERE context = 'normal' AND object = 'wal' \gset io_sum_wal_normal_after_
+SELECT current_setting('synchronous_commit') = 'on';
+SELECT :io_sum_wal_normal_after_writes > :io_sum_wal_normal_before_writes;
+SELECT current_setting('fsync') = 'off'
+  OR :io_sum_wal_normal_after_fsyncs > :io_sum_wal_normal_before_fsyncs;
 
 -- Change the tablespace so that the table is rewritten directly, then SELECT
 -- from it to cause it to be read back into shared buffers.