0001_pg_stat_walwrites_view.patch

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 7dcddf478a..d49e539da3 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -424,6 +424,14 @@ postgres   27093  0.0  0.0  30096  2752 ?        Ss   11:34   0:00 postgres: ser
      </entry>
      </row>
 
+     <row>
+      <entry><structname>pg_stat_walwrites</structname><indexterm><primary>pg_stat_walwrites</primary></indexterm></entry>
+      <entry>One row only, showing statistics about the
+       WAL writing activity. See
+       <xref linkend="monitoring-pg-stat-walwrites-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
@@ -3244,6 +3252,48 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
 
  </sect2>
 
+ <sect2 id="monitoring-pg-stat-walwrites-view">
+   <title><structname>pg_stat_walwrites</structname></title>
+
+  <indexterm>
+   <primary>pg_stat_walwrites</primary>
+  </indexterm>
+
+  <para>
+   The <structname>pg_stat_walwrites</structname> view will always have a
+   single row, containing data about the WAL writing activity of the cluster.
+  </para>
+
+  <table id="pg-stat-walwrites-view" xreflabel="pg_stat_walwrites">
+   <title><structname>pg_stat_walwrites</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>dirty_writes</structfield> <type>bigint</type>
+      </para>
+      <para>
+       Number of dirty WAL writes that are carried out by background processes and workers
+       when the <xref linkend="guc-wal-buffers"/> are full.
+      </para></entry>
+     </row>
+     </tbody>
+   </tgroup>
+  </table>
+
+</sect2>
+
  <sect2 id="monitoring-pg-stat-database-view">
   <title><structname>pg_stat_database</structname></title>
 
@@ -4632,8 +4682,9 @@ 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>walwrites</literal>
+        to reset all the counters shown in the <structname>pg_stat_walwrites</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 756b838e6a..66abd200d1 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -2193,6 +2193,7 @@ AdvanceXLInsertBuffer(XLogRecPtr upto, bool opportunistic)
 					WriteRqst.Write = OldPageRqstPtr;
 					WriteRqst.Flush = 0;
 					XLogWrite(WriteRqst, false);
+					WALWriteStats->dirty_writes++;
 					LWLockRelease(WALWriteLock);
 					TRACE_POSTGRESQL_WAL_BUFFER_WRITE_DIRTY_DONE();
 				}
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 8625cbeab6..cfc6a13b6a 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -994,6 +994,9 @@ CREATE VIEW pg_stat_progress_analyze AS
     FROM pg_stat_get_progress_info('ANALYZE') AS S
         LEFT JOIN pg_database D ON S.datid = D.oid;
 
+CREATE VIEW pg_stat_walwrites AS
+   SELECT * FROM pg_stat_get_walwrites() AS A;
+
 CREATE VIEW pg_stat_progress_vacuum AS
     SELECT
         S.pid AS pid, S.datid AS datid, D.datname AS datname,
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index 15f92b66c6..17feecd1a5 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -167,6 +167,15 @@ static const char *const slru_names[] = {
  */
 static PgStat_MsgSLRU SLRUStats[SLRU_NUM_ELEMENTS];
 
+/*
+ * WalWrites Local statistics counters.
+ * The statistics data gets populated in XLogWrite function.
+ * Stored directly in a stats message structure so it can be sent
+ * to stats collector process without needing to copy things around.
+ * We assume this inits to zeroes.
+ */
+PgStat_WalWritesStats *WALWriteStats;
+
 /* ----------
  * Local data
  * ----------
@@ -657,6 +666,29 @@ startup_failed:
 	SetConfigOption("track_counts", "off", PGC_INTERNAL, PGC_S_OVERRIDE);
 }
 
+/*
+ * Initialization of shared memory for WALWritesStats
+ */
+Size
+WALWritesShmemSize(void)
+{
+	return sizeof(PgStat_WalWritesStats);
+}
+
+void
+WALWritesShmemInit(void)
+{
+	bool		foundWALWrites;
+
+	WALWriteStats = (PgStat_WalWritesStats *)
+		ShmemInitStruct("WAL WriteStats", WALWritesShmemSize(), &foundWALWrites);
+
+	if (!foundWALWrites)
+	{
+		MemSet(WALWriteStats, 0, sizeof(PgStat_WalWritesStats));
+	}
+}
+
 /*
  * subroutine for pgstat_reset_all
  */
@@ -1370,11 +1402,25 @@ 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, "walwrites") == 0)
+	{
+		/*
+		 * Reset the wal writes statistics of the cluster. These statistics
+		 * are not reset by the stats collector because these are resides in a
+		 * shared memory, so it is not possible for the stats collector to
+		 * reset them. FIXME: This may need a sepearate function entirely to
+		 * reset the stats.
+		 */
+		LWLockAcquire(WALWriteLock, LW_EXCLUSIVE);
+		memset(WALWriteStats, 0, sizeof(PgStat_WalWritesStats));
+		WALWriteStats->stat_reset_timestamp = GetCurrentTimestamp();
+		LWLockRelease(WALWriteLock);
+	}
 	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\" or \"bgwriter\" or \"walwrites\".")));
 
 	pgstat_setheader(&msg.m_hdr, PGSTAT_MTYPE_RESETSHAREDCOUNTER);
 	pgstat_send(&msg, sizeof(msg));
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 96c2aaabbd..a49760ee24 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -149,6 +149,7 @@ CreateSharedMemoryAndSemaphores(void)
 		size = add_size(size, BTreeShmemSize());
 		size = add_size(size, SyncScanShmemSize());
 		size = add_size(size, AsyncShmemSize());
+		size = add_size(size, WALWritesShmemSize());
 #ifdef EXEC_BACKEND
 		size = add_size(size, ShmemBackendArraySize());
 #endif
@@ -216,6 +217,7 @@ CreateSharedMemoryAndSemaphores(void)
 	 * Set up xlog, clog, and buffers
 	 */
 	XLOGShmemInit();
+	WALWritesShmemInit();
 	CLOGShmemInit();
 	CommitTsShmemInit();
 	SUBTRANSShmemInit();
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 95738a4e34..12d762ef6a 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -2098,3 +2098,38 @@ pg_stat_get_archiver(PG_FUNCTION_ARGS)
 	/* Returns the record as Datum */
 	PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
 }
+
+Datum
+pg_stat_get_walwrites(PG_FUNCTION_ARGS)
+{
+	TupleDesc	tupdesc;
+	TimestampTz result;
+#define NUM_PG_STAT_WALWRITE_COLS 2
+	Datum		values[NUM_PG_STAT_WALWRITE_COLS];
+	bool		nulls[NUM_PG_STAT_WALWRITE_COLS];
+
+	/* Initialize values and NULL flags arrays */
+	MemSet(values, 0, sizeof(values));
+	MemSet(nulls, 0, sizeof(nulls));
+
+	/* Build a tuple descriptor for our result type */
+	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
+		elog(ERROR, "return type must be a row type");
+
+	LWLockAcquire(WALWriteLock, LW_EXCLUSIVE);
+
+	/* Get statistics about the archiver process */
+	/* Fill values and NULLs */
+	values[0] = Int64GetDatum(WALWriteStats->dirty_writes);
+
+	result = TimestampTzGetDatum(WALWriteStats->stat_reset_timestamp);
+	if (result == 0)
+		nulls[1] = true;
+	else
+		values[1] = result;
+
+	LWLockRelease(WALWriteLock);
+	/* Returns the record as Datum */
+	PG_RETURN_DATUM(HeapTupleGetDatum(
+									  heap_form_tuple(tupdesc, values, nulls)));
+}
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 082a11f270..f87bfdcfa9 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5484,6 +5484,14 @@
   proargnames => '{name,blks_zeroed,blks_hit,blks_read,blks_written,blks_exists,flushes,truncates,stats_reset}',
   prosrc => 'pg_stat_get_slru' },
 
+{ oid => '8000', descr => 'statistics: information about WAL writes activity',
+  proname => 'pg_stat_get_walwrites', provolatile => 's', proparallel => 'r',
+  prorettype => 'record', proargtypes => '',
+  proallargtypes => '{int8,timestamptz}',
+  proargmodes => '{o,o}',
+  proargnames => '{dirty_writes,stats_reset}',
+  prosrc => 'pg_stat_get_walwrites' },
+
 { oid => '2978', descr => 'statistics: number of function calls',
   proname => 'pg_stat_get_function_calls', provolatile => 's',
   proparallel => 'r', prorettype => 'int8', proargtypes => 'oid',
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 1387201382..94e4da6fd7 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -745,6 +745,19 @@ typedef struct PgStat_GlobalStats
 	TimestampTz stat_reset_timestamp;
 } PgStat_GlobalStats;
 
+/*
+ * Walwrites statistics kept in the stats collector
+ */
+typedef struct PgStat_WalWritesStats
+{
+	PgStat_Counter dirty_writes;	/* number of WAL write caused by full of WAL buffers */
+	TimestampTz stat_reset_timestamp;	/* last time when the stats reset */
+} PgStat_WalWritesStats;
+
+/* ----------
+ * Backend types
+ * ----------
+
 /*
  * SLRU statistics kept in the stats collector
  */
@@ -1260,6 +1273,11 @@ extern char *pgstat_stat_filename;
  */
 extern PgStat_MsgBgWriter BgWriterStats;
 
+/*
+ * WAL writes statistics updated in XLogWrite function
+ */
+extern PgStat_WalWritesStats * WALWriteStats;
+
 /*
  * Updated by pgstat_count_buffer_*_time macros
  */
@@ -1278,6 +1296,9 @@ extern int	pgstat_start(void);
 extern void pgstat_reset_all(void);
 extern void allow_immediate_pgstat_restart(void);
 
+extern Size WALWritesShmemSize(void);
+extern void WALWritesShmemInit(void);
+
 #ifdef EXEC_BACKEND
 extern void PgstatCollectorMain(int argc, char *argv[]) pg_attribute_noreturn();
 #endif
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 601734a6f1..3457cf2904 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -2136,6 +2136,9 @@ pg_stat_wal_receiver| SELECT s.pid,
     s.conninfo
    FROM pg_stat_get_wal_receiver() s(pid, status, receive_start_lsn, receive_start_tli, written_lsn, flushed_lsn, received_tli, last_msg_send_time, last_msg_receipt_time, latest_end_lsn, latest_end_time, slot_name, sender_host, sender_port, conninfo)
   WHERE (s.pid IS NOT NULL);
+pg_stat_walwrites| SELECT a.dirty_writes,
+    a.stats_reset
+   FROM pg_stat_get_walwrites() a(dirty_writes, stats_reset);
 pg_stat_xact_all_tables| SELECT c.oid AS relid,
     n.nspname AS schemaname,
     c.relname,
diff --git a/src/test/regress/expected/sysviews.out b/src/test/regress/expected/sysviews.out
index 06c4c3e476..3c04c57023 100644
--- a/src/test/regress/expected/sysviews.out
+++ b/src/test/regress/expected/sysviews.out
@@ -67,6 +67,13 @@ select count(*) >= 0 as ok from pg_prepared_xacts;
  t
 (1 row)
 
+-- There will surely and maximum one record
+select count(*) = 1 as ok from pg_stat_walwrites;
+ 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 28e412b735..21f49c9a3b 100644
--- a/src/test/regress/sql/sysviews.sql
+++ b/src/test/regress/sql/sysviews.sql
@@ -32,6 +32,9 @@ select count(*) = 0 as ok from pg_prepared_statements;
 -- See also prepared_xacts.sql
 select count(*) >= 0 as ok from pg_prepared_xacts;
 
+-- There will surely and maximum one record
+select count(*) = 1 as ok from pg_stat_walwrites;
+
 -- 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%';