Fix inconsistent reporting of checkpointer stats.

Previously, the pg_stat_checkpointer view and the checkpoint completion
log message could show different numbers for buffers written
during checkpoints. The view only counted shared buffers,
while the log message included both shared and SLRU buffers,
causing inconsistencies.

This commit resolves the issue by updating both the view and the log message
to separately report shared and SLRU buffers written during checkpoints.
A new slru_written column is added to the pg_stat_checkpointer view
to track SLRU buffers, while the existing buffers_written column now
tracks only shared buffers. This change would help users distinguish
between the two types of buffers, in the pg_stat_checkpointer view and
the checkpoint complete log message, respectively.

Bump catalog version.

Author: Nitin Jadhav
Reviewed-by: Bharath Rupireddy, Michael Paquier, Kyotaro Horiguchi, Robert Haas
Reviewed-by: Andres Freund, vignesh C, Fujii Masao
Discussion: https://postgr.es/m/CAMm1aWb18EpT0whJrjG+-nyhNouXET6ZUw0pNYYAe+NezpvsAA@mail.gmail.com

11 files changed, 47 insertions, 16 deletions

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 48ffe87241c..331315f8d3c 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3127,7 +3127,16 @@ description | Waiting for a newly initialized WAL file to reach durable storage
        <structfield>buffers_written</structfield> <type>bigint</type>
       </para>
       <para>
-       Number of buffers written during checkpoints and restartpoints
+       Number of shared buffers written during checkpoints and restartpoints
+      </para></entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry"><para role="column_definition">
+        <structfield>slru_written</structfield> <type>bigint</type>
+      </para>
+      <para>
+        Number of SLRU buffers written during checkpoints and restartpoints
       </para></entry>
      </row>
 
diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c
index e7f73bf4275..889eff1815b 100644
--- a/src/backend/access/transam/slru.c
+++ b/src/backend/access/transam/slru.c
@@ -716,9 +716,12 @@ SlruInternalWritePage(SlruCtl ctl, int slotno, SlruWriteAll fdata)
 	if (!ok)
 		SlruReportIOError(ctl, pageno, InvalidTransactionId);
 
-	/* If part of a checkpoint, count this as a buffer written. */
+	/* If part of a checkpoint, count this as a SLRU buffer written. */
 	if (fdata)
-		CheckpointStats.ckpt_bufs_written++;
+	{
+		CheckpointStats.ckpt_slru_written++;
+		PendingCheckpointerStats.slru_written++;
+	}
 }
 
 /*
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 64304d77d37..9102c8d772e 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -6727,14 +6727,15 @@ LogCheckpointEnd(bool restartpoint)
 	 */
 	if (restartpoint)
 		ereport(LOG,
-				(errmsg("restartpoint complete: wrote %d buffers (%.1f%%); "
-						"%d WAL file(s) added, %d removed, %d recycled; "
-						"write=%ld.%03d s, sync=%ld.%03d s, total=%ld.%03d s; "
-						"sync files=%d, longest=%ld.%03d s, average=%ld.%03d s; "
-						"distance=%d kB, estimate=%d kB; "
-						"lsn=%X/%X, redo lsn=%X/%X",
+				(errmsg("restartpoint complete: wrote %d buffers (%.1f%%), "
+						"wrote %d SLRU buffers; %d WAL file(s) added, "
+						"%d removed, %d recycled; write=%ld.%03d s, "
+						"sync=%ld.%03d s, total=%ld.%03d s; sync files=%d, "
+						"longest=%ld.%03d s, average=%ld.%03d s; distance=%d kB, "
+						"estimate=%d kB; lsn=%X/%X, redo lsn=%X/%X",
 						CheckpointStats.ckpt_bufs_written,
 						(double) CheckpointStats.ckpt_bufs_written * 100 / NBuffers,
+						CheckpointStats.ckpt_slru_written,
 						CheckpointStats.ckpt_segs_added,
 						CheckpointStats.ckpt_segs_removed,
 						CheckpointStats.ckpt_segs_recycled,
@@ -6750,14 +6751,15 @@ LogCheckpointEnd(bool restartpoint)
 						LSN_FORMAT_ARGS(ControlFile->checkPointCopy.redo))));
 	else
 		ereport(LOG,
-				(errmsg("checkpoint complete: wrote %d buffers (%.1f%%); "
-						"%d WAL file(s) added, %d removed, %d recycled; "
-						"write=%ld.%03d s, sync=%ld.%03d s, total=%ld.%03d s; "
-						"sync files=%d, longest=%ld.%03d s, average=%ld.%03d s; "
-						"distance=%d kB, estimate=%d kB; "
-						"lsn=%X/%X, redo lsn=%X/%X",
+				(errmsg("checkpoint complete: wrote %d buffers (%.1f%%), "
+						"wrote %d SLRU buffers; %d WAL file(s) added, "
+						"%d removed, %d recycled; write=%ld.%03d s, "
+						"sync=%ld.%03d s, total=%ld.%03d s; sync files=%d, "
+						"longest=%ld.%03d s, average=%ld.%03d s; distance=%d kB, "
+						"estimate=%d kB; lsn=%X/%X, redo lsn=%X/%X",
 						CheckpointStats.ckpt_bufs_written,
 						(double) CheckpointStats.ckpt_bufs_written * 100 / NBuffers,
+						CheckpointStats.ckpt_slru_written,
 						CheckpointStats.ckpt_segs_added,
 						CheckpointStats.ckpt_segs_removed,
 						CheckpointStats.ckpt_segs_recycled,
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 49109dbdc86..3456b821bc5 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1145,6 +1145,7 @@ CREATE VIEW pg_stat_checkpointer AS
         pg_stat_get_checkpointer_write_time() AS write_time,
         pg_stat_get_checkpointer_sync_time() AS sync_time,
         pg_stat_get_checkpointer_buffers_written() AS buffers_written,
+        pg_stat_get_checkpointer_slru_written() AS slru_written,
         pg_stat_get_checkpointer_stat_reset_time() AS stats_reset;
 
 CREATE VIEW pg_stat_io AS
diff --git a/src/backend/utils/activity/pgstat_checkpointer.c b/src/backend/utils/activity/pgstat_checkpointer.c
index 4a0a2d1493a..5a3fb4a9e09 100644
--- a/src/backend/utils/activity/pgstat_checkpointer.c
+++ b/src/backend/utils/activity/pgstat_checkpointer.c
@@ -56,6 +56,7 @@ pgstat_report_checkpointer(void)
 	CHECKPOINTER_ACC(write_time);
 	CHECKPOINTER_ACC(sync_time);
 	CHECKPOINTER_ACC(buffers_written);
+	CHECKPOINTER_ACC(slru_written);
 #undef CHECKPOINTER_ACC
 
 	pgstat_end_changecount_write(&stats_shmem->changecount);
@@ -135,5 +136,6 @@ pgstat_checkpointer_snapshot_cb(void)
 	CHECKPOINTER_COMP(write_time);
 	CHECKPOINTER_COMP(sync_time);
 	CHECKPOINTER_COMP(buffers_written);
+	CHECKPOINTER_COMP(slru_written);
 #undef CHECKPOINTER_COMP
 }
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 17b0fc02ef0..f7b50e0b5af 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1222,6 +1222,12 @@ pg_stat_get_checkpointer_buffers_written(PG_FUNCTION_ARGS)
 }
 
 Datum
+pg_stat_get_checkpointer_slru_written(PG_FUNCTION_ARGS)
+{
+	PG_RETURN_INT64(pgstat_fetch_stat_checkpointer()->slru_written);
+}
+
+Datum
 pg_stat_get_bgwriter_buf_written_clean(PG_FUNCTION_ARGS)
 {
 	PG_RETURN_INT64(pgstat_fetch_stat_bgwriter()->buf_written_clean);
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index 36f6e4e4b4e..34ad46c067b 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -167,6 +167,7 @@ typedef struct CheckpointStatsData
 	TimestampTz ckpt_end_t;		/* end of checkpoint */
 
 	int			ckpt_bufs_written;	/* # of buffers written */
+	int			ckpt_slru_written;	/* # of SLRU buffers written */
 
 	int			ckpt_segs_added;	/* # of new xlog segments created */
 	int			ckpt_segs_removed;	/* # of xlog segments deleted */
diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index 3c89b70f9e4..504bbe53276 100644
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -57,6 +57,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	202409302
+#define CATALOG_VERSION_NO	202410021
 
 #endif
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 05fcbf75156..77f54a79e6a 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5847,6 +5847,11 @@
   proname => 'pg_stat_get_checkpointer_buffers_written', provolatile => 's',
   proparallel => 'r', prorettype => 'int8', proargtypes => '',
   prosrc => 'pg_stat_get_checkpointer_buffers_written' },
+{ oid => '8573',
+  descr => 'statistics: number of SLRU buffers written during checkpoints and restartpoints',
+  proname => 'pg_stat_get_checkpointer_slru_written', provolatile => 's',
+  proparallel => 'r', prorettype => 'int8', proargtypes => '',
+  prosrc => 'pg_stat_get_checkpointer_slru_written' },
 { oid => '6314', descr => 'statistics: last reset for the checkpointer',
   proname => 'pg_stat_get_checkpointer_stat_reset_time', provolatile => 's',
   proparallel => 'r', prorettype => 'timestamptz', proargtypes => '',
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 476acd680c0..df53fa2d4f9 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -301,6 +301,7 @@ typedef struct PgStat_CheckpointerStats
 	PgStat_Counter write_time;	/* times in milliseconds */
 	PgStat_Counter sync_time;
 	PgStat_Counter buffers_written;
+	PgStat_Counter slru_written;
 	TimestampTz stat_reset_timestamp;
 } PgStat_CheckpointerStats;
 
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index f5434d8365c..2b47013f113 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1831,6 +1831,7 @@ pg_stat_checkpointer| SELECT pg_stat_get_checkpointer_num_timed() AS num_timed,
     pg_stat_get_checkpointer_write_time() AS write_time,
     pg_stat_get_checkpointer_sync_time() AS sync_time,
     pg_stat_get_checkpointer_buffers_written() AS buffers_written,
+    pg_stat_get_checkpointer_slru_written() AS slru_written,
     pg_stat_get_checkpointer_stat_reset_time() AS stats_reset;
 pg_stat_database| SELECT oid AS datid,
     datname,