On 2020-09-18 11:11, Kyotaro Horiguchi wrote:
At Fri, 18 Sep 2020 09:40:11 +0900, Masahiro Ikeda
<ikeda...@oss.nttdata.com> wrote in
Thanks. I confirmed that it causes HOT pruning or killing of
dead index tuple if DecodeCommit() is called.
As you said, DecodeCommit() may access the system table.
...
The wals are generated only when logical replication is performed.
So, I added pgstat_send_wal() in XLogSendLogical().
But, I concerned that it causes poor performance
since pgstat_send_wal() is called per wal record,
I think that's too frequent. If we want to send any stats to the
collector, it is usually done at commit time using
pgstat_report_stat(), and the function avoids sending stats too
frequently. For logrep-worker, apply_handle_commit() is calling it. It
seems to be the place if we want to send the wal stats. Or it may be
better to call pgstat_send_wal() via pgstat_report_stat(), like
pg_stat_slru().
Thanks for your comments.
Since I changed to use pgstat_report_stat() and DecodeCommit() is
calling it,
the frequency to send statistics is not so high.
Currently logrep-laucher, logrep-worker and autovac-launcher (and some
other processes?) don't seem (AFAICS) sending scan stats at all but
according to the discussion here, we should let such processes send
stats.
I added pgstat_report_stat() to logrep-laucher and autovac-launcher.
As you said, logrep-worker already calls apply_handle_commit() and
pgstat_report_stat().
The checkpointer doesn't seem to call pgstat_report_stat() currently,
but since there is a possibility to send wal statistics, I added
pgstat_report_stat().
Regards,
--
Masahiro Ikeda
NTT DATA CORPORATION
diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 4e0193a967..dd292fe27c 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -424,6 +424,13 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser
</entry>
</row>
+ <row>
+ <entry><structname>pg_stat_wal</structname><indexterm><primary>pg_stat_wal</primary></indexterm></entry>
+ <entry>One row only, showing statistics about the WAL writing activity. See
+ <xref linkend="monitoring-pg-stat-wal-view"/> for details.
+ </entry>
+ </row>
+
<row>
<entry><structname>pg_stat_database</structname><indexterm><primary>pg_stat_database</primary></indexterm></entry>
<entry>One row per database, showing database-wide statistics. See
@@ -3280,6 +3287,56 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
</sect2>
+ <sect2 id="monitoring-pg-stat-wal-view">
+ <title><structname>pg_stat_wal</structname></title>
+
+ <indexterm>
+ <primary>pg_stat_wal</primary>
+ </indexterm>
+
+ <para>
+ The <structname>pg_stat_wal</structname> view will always have a
+ single row, containing data about the WAL writing activity of the cluster.
+ </para>
+
+ <table id="pg-stat-wal-view" xreflabel="pg_stat_wal">
+ <title><structname>pg_stat_wal</structname> View</title>
+ <tgroup cols="1">
+ <thead>
+ <row>
+ <entry role="catalog_table_entry"><para role="column_definition">
+ Column Type
+ </para>
+ <para>
+ Description
+ </para></entry>
+ </row>
+ </thead>
+
+ <tbody>
+ <row>
+ <entry role="catalog_table_entry"><para role="column_definition">
+ <structfield>wal_buffers_full</structfield> <type>bigint</type>
+ </para>
+ <para>
+ Number of WAL writes when the <xref linkend="guc-wal-buffers"/> are full
+ </para></entry>
+ </row>
+
+ <row>
+ <entry role="catalog_table_entry"><para role="column_definition">
+ <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
+ </para>
+ <para>
+ Time at which these statistics were last reset
+ </para></entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+
+</sect2>
+
<sect2 id="monitoring-pg-stat-database-view">
<title><structname>pg_stat_database</structname></title>
@@ -4668,8 +4725,9 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
argument. The argument can be <literal>bgwriter</literal> to reset
all the counters shown in
the <structname>pg_stat_bgwriter</structname>
- view, or <literal>archiver</literal> to reset all the counters shown in
- the <structname>pg_stat_archiver</structname> view.
+ view, <literal>archiver</literal> to reset all the counters shown in
+ the <structname>pg_stat_archiver</structname> view ,or <literal>wal</literal>
+ to reset all the counters shown in the <structname>pg_stat_wal</structname> view.
</para>
<para>
This function is restricted to superusers by default, but other users
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 61754312e2..3a06cacefb 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -2195,6 +2195,7 @@ AdvanceXLInsertBuffer(XLogRecPtr upto, bool opportunistic)
WriteRqst.Flush = 0;
XLogWrite(WriteRqst, false);
LWLockRelease(WALWriteLock);
+ WalStats.m_wal_buffers_full++;
TRACE_POSTGRESQL_WAL_BUFFER_WRITE_DIRTY_DONE();
}
/* Re-acquire WALBufMappingLock and retry */
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index ed4f3f142d..643445c189 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -979,6 +979,11 @@ CREATE VIEW pg_stat_bgwriter AS
pg_stat_get_buf_alloc() AS buffers_alloc,
pg_stat_get_bgwriter_stat_reset_time() AS stats_reset;
+CREATE VIEW pg_stat_wal AS
+ SELECT
+ pg_stat_get_wal_buffers_full() AS wal_buffers_full,
+ pg_stat_get_wal_stat_reset_time() AS stats_reset;
+
CREATE VIEW pg_stat_progress_analyze AS
SELECT
S.pid AS pid, S.datid AS datid, D.datname AS datname,
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 2cef56f115..1b224d479d 100644
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -795,6 +795,8 @@ AutoVacLauncherMain(int argc, char *argv[])
current_time, 0))
launch_worker(current_time);
}
+
+ pgstat_report_stat(false);
}
AutoVacLauncherShutdown();
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index 3e7dcd4f76..a4dce85955 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -503,6 +503,7 @@ CheckpointerMain(void)
* stats message types.)
*/
pgstat_send_bgwriter();
+ pgstat_report_stat(false);
/*
* If any checkpoint flags have been set, redo the loop to handle the
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index e6be2b7836..7127beca66 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -141,6 +141,13 @@ char *pgstat_stat_tmpname = NULL;
*/
PgStat_MsgBgWriter BgWriterStats;
+/*
+ * WAL global statistics counter.
+ * This counter is incremented by both each backend and background.
+ * And then, sent to the stat collector process.
+ */
+PgStat_MsgWal WalStats;
+
/*
* List of SLRU names that we keep stats for. There is no central registry of
* SLRUs, so we use this fixed list instead. The "other" entry is used for
@@ -281,6 +288,7 @@ static int localNumBackends = 0;
*/
static PgStat_ArchiverStats archiverStats;
static PgStat_GlobalStats globalStats;
+static PgStat_WalStats walStats;
static PgStat_SLRUStats slruStats[SLRU_NUM_ELEMENTS];
/*
@@ -353,6 +361,7 @@ static void pgstat_recv_vacuum(PgStat_MsgVacuum *msg, int len);
static void pgstat_recv_analyze(PgStat_MsgAnalyze *msg, int len);
static void pgstat_recv_archiver(PgStat_MsgArchiver *msg, int len);
static void pgstat_recv_bgwriter(PgStat_MsgBgWriter *msg, int len);
+static void pgstat_recv_wal(PgStat_MsgWal *msg, int len);
static void pgstat_recv_slru(PgStat_MsgSLRU *msg, int len);
static void pgstat_recv_funcstat(PgStat_MsgFuncstat *msg, int len);
static void pgstat_recv_funcpurge(PgStat_MsgFuncpurge *msg, int len);
@@ -938,6 +947,9 @@ pgstat_report_stat(bool force)
/* Now, send function statistics */
pgstat_send_funcstats();
+ /* Send wal statistics */
+ pgstat_send_wal();
+
/* Finally send SLRU statistics */
pgstat_send_slru();
}
@@ -1370,11 +1382,13 @@ pgstat_reset_shared_counters(const char *target)
msg.m_resettarget = RESET_ARCHIVER;
else if (strcmp(target, "bgwriter") == 0)
msg.m_resettarget = RESET_BGWRITER;
+ else if (strcmp(target, "wal") == 0)
+ msg.m_resettarget = RESET_WAL;
else
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("unrecognized reset target: \"%s\"", target),
- errhint("Target must be \"archiver\" or \"bgwriter\".")));
+ errhint("Target must be \"archiver\", \"bgwriter\" or \"wal\".")));
pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETSHAREDCOUNTER);
pgstat_send(&msg, sizeof(msg));
@@ -2674,6 +2688,21 @@ pgstat_fetch_global(void)
return &globalStats;
}
+/*
+ * ---------
+ * pgstat_fetch_stat_wal() -
+ *
+ * Support function for the SQL-callable pgstat* functions. Returns
+ * a pointer to the wal statistics struct.
+ * ---------
+ */
+PgStat_WalStats *
+pgstat_fetch_stat_wal(void)
+{
+ backend_read_statsfile();
+
+ return &walStats;
+}
/*
* ---------
@@ -4419,6 +4448,38 @@ pgstat_send_bgwriter(void)
MemSet(&BgWriterStats, 0, sizeof(BgWriterStats));
}
+/* ----------
+ * pgstat_send_wal() -
+ *
+ * Send wal statistics to the collector
+ * ----------
+ */
+void
+pgstat_send_wal(void)
+{
+ /* We assume this initializes to zeroes */
+ static const PgStat_MsgWal all_zeroes;
+
+ /*
+ * This function can be called even if nothing at all has happened. In
+ * this case, avoid sending a completely empty message to the stats
+ * collector.
+ */
+ if (memcmp(&WalStats, &all_zeroes, sizeof(PgStat_MsgWal)) == 0)
+ return;
+
+ /*
+ * Prepare and send the message
+ */
+ pgstat_setheader(&WalStats.m_hdr, PGSTAT_MTYPE_WAL);
+ pgstat_send(&WalStats, sizeof(WalStats));
+
+ /*
+ * Clear out the statistics buffer, so it can be re-used.
+ */
+ MemSet(&WalStats, 0, sizeof(WalStats));
+}
+
/* ----------
* pgstat_send_slru() -
*
@@ -4658,6 +4719,10 @@ PgstatCollectorMain(int argc, char *argv[])
pgstat_recv_bgwriter(&msg.msg_bgwriter, len);
break;
+ case PGSTAT_MTYPE_WAL:
+ pgstat_recv_wal(&msg.msg_wal, len);
+ break;
+
case PGSTAT_MTYPE_SLRU:
pgstat_recv_slru(&msg.msg_slru, len);
break;
@@ -4927,6 +4992,12 @@ pgstat_write_statsfiles(bool permanent, bool allDbs)
rc = fwrite(&archiverStats, sizeof(archiverStats), 1, fpout);
(void) rc; /* we'll check for error with ferror */
+ /*
+ * Write wal stats struct
+ */
+ rc = fwrite(&walStats, sizeof(walStats), 1, fpout);
+ (void) rc; /* we'll check for error with ferror */
+
/*
* Write SLRU stats struct
*/
@@ -5186,11 +5257,12 @@ pgstat_read_statsfiles(Oid onlydb, bool permanent, bool deep)
HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
/*
- * Clear out global and archiver statistics so they start from zero in
+ * Clear out global, archiver and wal statistics so they start from zero in
* case we can't load an existing statsfile.
*/
memset(&globalStats, 0, sizeof(globalStats));
memset(&archiverStats, 0, sizeof(archiverStats));
+ memset(&walStats, 0, sizeof(walStats));
memset(&slruStats, 0, sizeof(slruStats));
/*
@@ -5199,6 +5271,7 @@ pgstat_read_statsfiles(Oid onlydb, bool permanent, bool deep)
*/
globalStats.stat_reset_timestamp = GetCurrentTimestamp();
archiverStats.stat_reset_timestamp = globalStats.stat_reset_timestamp;
+ walStats.stat_reset_timestamp = globalStats.stat_reset_timestamp;
/*
* Set the same reset timestamp for all SLRU items too.
@@ -5268,6 +5341,17 @@ pgstat_read_statsfiles(Oid onlydb, bool permanent, bool deep)
goto done;
}
+ /*
+ * Read wal stats struct
+ */
+ if (fread(&walStats, 1, sizeof(walStats), fpin) != sizeof(walStats))
+ {
+ ereport(pgStatRunningInCollector ? LOG : WARNING,
+ (errmsg("corrupted statistics file \"%s\"", statfile)));
+ memset(&walStats, 0, sizeof(walStats));
+ goto done;
+ }
+
/*
* Read SLRU stats struct
*/
@@ -5633,6 +5717,17 @@ pgstat_read_db_statsfile_timestamp(Oid databaseid, bool permanent,
return false;
}
+ /*
+ * Read wal stats struct
+ */
+ if (fread(&walStats, 1, sizeof(walStats), fpin) != sizeof(walStats))
+ {
+ ereport(pgStatRunningInCollector ? LOG : WARNING,
+ (errmsg("corrupted statistics file \"%s\"", statfile)));
+ FreeFile(fpin);
+ return false;
+ }
+
/*
* Read SLRU stats struct
*/
@@ -6213,6 +6308,12 @@ pgstat_recv_resetsharedcounter(PgStat_MsgResetsharedcounter *msg, int len)
memset(&archiverStats, 0, sizeof(archiverStats));
archiverStats.stat_reset_timestamp = GetCurrentTimestamp();
}
+ else if (msg->m_resettarget == RESET_WAL)
+ {
+ /* Reset the wal statistics for the cluster. */
+ memset(&walStats, 0, sizeof(walStats));
+ walStats.stat_reset_timestamp = GetCurrentTimestamp();
+ }
/*
* Presumably the sender of this message validated the target, don't
@@ -6427,6 +6528,18 @@ pgstat_recv_bgwriter(PgStat_MsgBgWriter *msg, int len)
globalStats.buf_alloc += msg->m_buf_alloc;
}
+/* ----------
+ * pgstat_recv_wal() -
+ *
+ * Process a WAL message.
+ * ----------
+ */
+static void
+pgstat_recv_wal(PgStat_MsgWal *msg, int len)
+{
+ walStats.wal_buffers_full += msg->m_wal_buffers_full;
+}
+
/* ----------
* pgstat_recv_slru() -
*
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index f21f61d5e1..80ee18ce19 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -650,6 +650,7 @@ DecodeCommit(LogicalDecodingContext *ctx, XLogRecordBuffer *buf,
/* replay actions of all transaction + subtransactions in order */
ReorderBufferCommit(ctx->reorder, xid, buf->origptr, buf->endptr,
commit_time, origin_id, origin_lsn);
+ pgstat_report_stat(false);
}
/*
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index bdaf0312d6..dba86e8471 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1025,6 +1025,8 @@ ApplyLauncherMain(Datum main_arg)
MemoryContextSwitchTo(oldctx);
/* Clean the temporary memory. */
MemoryContextDelete(subctx);
+
+ pgstat_report_stat(false);
}
else
{
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 95738a4e34..aa41330796 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1697,6 +1697,18 @@ pg_stat_get_buf_alloc(PG_FUNCTION_ARGS)
PG_RETURN_INT64(pgstat_fetch_global()->buf_alloc);
}
+Datum
+pg_stat_get_wal_buffers_full(PG_FUNCTION_ARGS)
+{
+ PG_RETURN_INT64(pgstat_fetch_stat_wal()->wal_buffers_full);
+}
+
+Datum
+pg_stat_get_wal_stat_reset_time(PG_FUNCTION_ARGS)
+{
+ PG_RETURN_TIMESTAMPTZ(pgstat_fetch_stat_wal()->stat_reset_timestamp);
+}
+
/*
* Returns statistics of SLRU caches.
*/
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index f48f5fb4d9..5b1830274a 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5481,6 +5481,14 @@
proname => 'pg_stat_get_buf_alloc', provolatile => 's', proparallel => 'r',
prorettype => 'int8', proargtypes => '', prosrc => 'pg_stat_get_buf_alloc' },
+{ oid => '1136', descr => 'statistics: number of WAL writes when the wal buffers are full',
+ proname => 'pg_stat_get_wal_buffers_full', provolatile => 's', proparallel => 'r',
+ prorettype => 'int8', proargtypes => '', prosrc => 'pg_stat_get_wal_buffers_full' },
+{ oid => '1137', descr => 'statistics: last reset for the walwriter',
+ proname => 'pg_stat_get_wal_stat_reset_time', provolatile => 's',
+ proparallel => 'r', prorettype => 'timestamptz', proargtypes => '',
+ prosrc => 'pg_stat_get_wal_stat_reset_time' },
+
{ oid => '2306', descr => 'statistics: information about SLRU caches',
proname => 'pg_stat_get_slru', prorows => '100', proisstrict => 'f',
proretset => 't', provolatile => 's', proparallel => 'r',
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 0dfbac46b4..eb706068ba 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -61,6 +61,7 @@ typedef enum StatMsgType
PGSTAT_MTYPE_ANALYZE,
PGSTAT_MTYPE_ARCHIVER,
PGSTAT_MTYPE_BGWRITER,
+ PGSTAT_MTYPE_WAL,
PGSTAT_MTYPE_SLRU,
PGSTAT_MTYPE_FUNCSTAT,
PGSTAT_MTYPE_FUNCPURGE,
@@ -122,7 +123,8 @@ typedef struct PgStat_TableCounts
typedef enum PgStat_Shared_Reset_Target
{
RESET_ARCHIVER,
- RESET_BGWRITER
+ RESET_BGWRITER,
+ RESET_WAL
} PgStat_Shared_Reset_Target;
/* Possible object types for resetting single counters */
@@ -436,6 +438,16 @@ typedef struct PgStat_MsgBgWriter
PgStat_Counter m_checkpoint_sync_time;
} PgStat_MsgBgWriter;
+/* ----------
+ * PgStat_MsgWal Sent by each backend and background workers to update WAL statistics.
+ * ----------
+ */
+typedef struct PgStat_MsgWal
+{
+ PgStat_MsgHdr m_hdr;
+ PgStat_Counter m_wal_buffers_full; /* number of WAL write caused by full of WAL buffers */
+} PgStat_MsgWal;
+
/* ----------
* PgStat_MsgSLRU Sent by a backend to update SLRU statistics.
* ----------
@@ -596,6 +608,7 @@ typedef union PgStat_Msg
PgStat_MsgAnalyze msg_analyze;
PgStat_MsgArchiver msg_archiver;
PgStat_MsgBgWriter msg_bgwriter;
+ PgStat_MsgWal msg_wal;
PgStat_MsgSLRU msg_slru;
PgStat_MsgFuncstat msg_funcstat;
PgStat_MsgFuncpurge msg_funcpurge;
@@ -745,6 +758,15 @@ typedef struct PgStat_GlobalStats
TimestampTz stat_reset_timestamp;
} PgStat_GlobalStats;
+/*
+ * WAL statistics kept in the stats collector
+ */
+typedef struct PgStat_WalStats
+{
+ PgStat_Counter wal_buffers_full; /* number of WAL write caused by full of WAL buffers */
+ TimestampTz stat_reset_timestamp; /* last time when the stats reset */
+} PgStat_WalStats;
+
/*
* SLRU statistics kept in the stats collector
*/
@@ -1265,6 +1287,11 @@ extern char *pgstat_stat_filename;
*/
extern PgStat_MsgBgWriter BgWriterStats;
+/*
+ * WAL writes statistics counter is updated by backend and background workers
+ */
+extern PgStat_MsgWal WalStats;
+
/*
* Updated by pgstat_count_buffer_*_time macros
*/
@@ -1464,6 +1491,7 @@ extern void pgstat_twophase_postabort(TransactionId xid, uint16 info,
extern void pgstat_send_archiver(const char *xlog, bool failed);
extern void pgstat_send_bgwriter(void);
+extern void pgstat_send_wal(void);
/* ----------
* Support functions for the SQL-callable functions to
@@ -1478,6 +1506,7 @@ extern PgStat_StatFuncEntry *pgstat_fetch_stat_funcentry(Oid funcid);
extern int pgstat_fetch_stat_numbackends(void);
extern PgStat_ArchiverStats *pgstat_fetch_stat_archiver(void);
extern PgStat_GlobalStats *pgstat_fetch_global(void);
+extern PgStat_WalStats *pgstat_fetch_stat_wal(void);
extern PgStat_SLRUStats *pgstat_fetch_slru(void);
extern void pgstat_count_slru_page_zeroed(int slru_idx);
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 2a18dc423e..1e4ac4432e 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -2129,6 +2129,8 @@ pg_stat_user_tables| SELECT pg_stat_all_tables.relid,
pg_stat_all_tables.autoanalyze_count
FROM pg_stat_all_tables
WHERE ((pg_stat_all_tables.schemaname <> ALL (ARRAY['pg_catalog'::name, 'information_schema'::name])) AND (pg_stat_all_tables.schemaname !~ '^pg_toast'::text));
+pg_stat_wal| SELECT pg_stat_get_wal_buffers_full() AS wal_buffers_full,
+ pg_stat_get_wal_stat_reset_time() AS stats_reset;
pg_stat_wal_receiver| SELECT s.pid,
s.status,
s.receive_start_lsn,
diff --git a/src/test/regress/expected/sysviews.out b/src/test/regress/expected/sysviews.out
index 1cffc3349d..81bdacf59d 100644
--- a/src/test/regress/expected/sysviews.out
+++ b/src/test/regress/expected/sysviews.out
@@ -76,6 +76,13 @@ select count(*) >= 0 as ok from pg_prepared_xacts;
t
(1 row)
+-- There must be only one record
+select count(*) = 1 as ok from pg_stat_wal;
+ ok
+----
+ t
+(1 row)
+
-- This is to record the prevailing planner enable_foo settings during
-- a regression test run.
select name, setting from pg_settings where name like 'enable%';
diff --git a/src/test/regress/sql/sysviews.sql b/src/test/regress/sql/sysviews.sql
index ac4a0e1cbb..b9b875bc6a 100644
--- a/src/test/regress/sql/sysviews.sql
+++ b/src/test/regress/sql/sysviews.sql
@@ -37,6 +37,9 @@ select count(*) = 0 as ok from pg_prepared_statements;
-- See also prepared_xacts.sql
select count(*) >= 0 as ok from pg_prepared_xacts;
+-- There must be only one record
+select count(*) = 1 as ok from pg_stat_wal;
+
-- This is to record the prevailing planner enable_foo settings during
-- a regression test run.
select name, setting from pg_settings where name like 'enable%';
