Introduce pg_stat_checkpointer

Historically, the statistics of the checkpointer have been always part
of pg_stat_bgwriter.  This commit removes a few columns from
pg_stat_bgwriter, and introduces pg_stat_checkpointer with equivalent,
renamed columns (plus a new one for the reset timestamp):
- checkpoints_timed -> num_timed
- checkpoints_req -> num_requested
- checkpoint_write_time -> write_time
- checkpoint_sync_time -> sync_time
- buffers_checkpoint -> buffers_written

The fields of PgStat_CheckpointerStats and its SQL functions are renamed
to match with the new field names, for consistency.  Note that
background writer and checkpointer have been split into two different
processes in commits 806a2aee3791 and bf405ba8e460.  The pgstat
structures were already split, making this change straight-forward.

Bump catalog version.

Author: Bharath Rupireddy
Reviewed-by: Bertrand Drouvot, Andres Freund, Michael Paquier
Discussion: https://postgr.es/m/CALj2ACVxX2ii=66RypXRweZe2EsBRiPMj0aHfRfHUeXJcC7kHg@mail.gmail.com

6 files changed, 44 insertions, 38 deletions

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 40461923ea3..b541be8eec2 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -6349,8 +6349,8 @@ LogCheckpointEnd(bool restartpoint)
 												 CheckpointStats.ckpt_sync_end_t);
 
 	/* Accumulate checkpoint timing summary data, in milliseconds. */
-	PendingCheckpointerStats.checkpoint_write_time += write_msecs;
-	PendingCheckpointerStats.checkpoint_sync_time += sync_msecs;
+	PendingCheckpointerStats.write_time += write_msecs;
+	PendingCheckpointerStats.sync_time += sync_msecs;
 
 	/*
 	 * All of the published timing statistics are accounted for.  Only
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 886f175fc2d..b65f6b52490 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1111,16 +1111,20 @@ CREATE VIEW pg_stat_archiver AS
 
 CREATE VIEW pg_stat_bgwriter AS
     SELECT
-        pg_stat_get_bgwriter_timed_checkpoints() AS checkpoints_timed,
-        pg_stat_get_bgwriter_requested_checkpoints() AS checkpoints_req,
-        pg_stat_get_checkpoint_write_time() AS checkpoint_write_time,
-        pg_stat_get_checkpoint_sync_time() AS checkpoint_sync_time,
-        pg_stat_get_bgwriter_buf_written_checkpoints() AS buffers_checkpoint,
         pg_stat_get_bgwriter_buf_written_clean() AS buffers_clean,
         pg_stat_get_bgwriter_maxwritten_clean() AS maxwritten_clean,
         pg_stat_get_buf_alloc() AS buffers_alloc,
         pg_stat_get_bgwriter_stat_reset_time() AS stats_reset;
 
+CREATE VIEW pg_stat_checkpointer AS
+    SELECT
+        pg_stat_get_checkpointer_num_timed() AS num_timed,
+        pg_stat_get_checkpointer_num_requested() AS num_requested,
+        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_stat_reset_time() AS stats_reset;
+
 CREATE VIEW pg_stat_io AS
 SELECT
        b.backend_type,
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index 4fe403c9a89..a3c1aba24ea 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -358,7 +358,7 @@ CheckpointerMain(void)
 		if (((volatile CheckpointerShmemStruct *) CheckpointerShmem)->ckpt_flags)
 		{
 			do_checkpoint = true;
-			PendingCheckpointerStats.requested_checkpoints++;
+			PendingCheckpointerStats.num_requested++;
 		}
 
 		/*
@@ -372,7 +372,7 @@ CheckpointerMain(void)
 		if (elapsed_secs >= CheckPointTimeout)
 		{
 			if (!do_checkpoint)
-				PendingCheckpointerStats.timed_checkpoints++;
+				PendingCheckpointerStats.num_timed++;
 			do_checkpoint = true;
 			flags |= CHECKPOINT_CAUSE_TIME;
 		}
@@ -569,7 +569,7 @@ HandleCheckpointerInterrupts(void)
 		 * updates the statistics, increment the checkpoint request and flush
 		 * out pending statistic.
 		 */
-		PendingCheckpointerStats.requested_checkpoints++;
+		PendingCheckpointerStats.num_requested++;
 		ShutdownXLOG(0, 0);
 		pgstat_report_checkpointer();
 		pgstat_report_wal(true);
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 21a29f9081a..dc504a1ae00 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -2751,7 +2751,7 @@ BufferSync(int flags)
 			if (SyncOneBuffer(buf_id, false, &wb_context) & BUF_WRITTEN)
 			{
 				TRACE_POSTGRESQL_BUFFER_SYNC_WRITTEN(buf_id);
-				PendingCheckpointerStats.buf_written_checkpoints++;
+				PendingCheckpointerStats.buffers_written++;
 				num_written++;
 			}
 		}
diff --git a/src/backend/utils/activity/pgstat_checkpointer.c b/src/backend/utils/activity/pgstat_checkpointer.c
index 03ed5dddda7..301a0bc7bd3 100644
--- a/src/backend/utils/activity/pgstat_checkpointer.c
+++ b/src/backend/utils/activity/pgstat_checkpointer.c
@@ -47,11 +47,11 @@ pgstat_report_checkpointer(void)
 	pgstat_begin_changecount_write(&stats_shmem->changecount);
 
 #define CHECKPOINTER_ACC(fld) stats_shmem->stats.fld += PendingCheckpointerStats.fld
-	CHECKPOINTER_ACC(timed_checkpoints);
-	CHECKPOINTER_ACC(requested_checkpoints);
-	CHECKPOINTER_ACC(checkpoint_write_time);
-	CHECKPOINTER_ACC(checkpoint_sync_time);
-	CHECKPOINTER_ACC(buf_written_checkpoints);
+	CHECKPOINTER_ACC(num_timed);
+	CHECKPOINTER_ACC(num_requested);
+	CHECKPOINTER_ACC(write_time);
+	CHECKPOINTER_ACC(sync_time);
+	CHECKPOINTER_ACC(buffers_written);
 #undef CHECKPOINTER_ACC
 
 	pgstat_end_changecount_write(&stats_shmem->changecount);
@@ -92,6 +92,7 @@ pgstat_checkpointer_reset_all_cb(TimestampTz ts)
 									&stats_shmem->stats,
 									sizeof(stats_shmem->stats),
 									&stats_shmem->changecount);
+	stats_shmem->stats.stat_reset_timestamp = ts;
 	LWLockRelease(&stats_shmem->lock);
 }
 
@@ -113,10 +114,10 @@ pgstat_checkpointer_snapshot_cb(void)
 
 	/* compensate by reset offsets */
 #define CHECKPOINTER_COMP(fld) pgStatLocal.snapshot.checkpointer.fld -= reset.fld;
-	CHECKPOINTER_COMP(timed_checkpoints);
-	CHECKPOINTER_COMP(requested_checkpoints);
-	CHECKPOINTER_COMP(checkpoint_write_time);
-	CHECKPOINTER_COMP(checkpoint_sync_time);
-	CHECKPOINTER_COMP(buf_written_checkpoints);
+	CHECKPOINTER_COMP(num_timed);
+	CHECKPOINTER_COMP(num_requested);
+	CHECKPOINTER_COMP(write_time);
+	CHECKPOINTER_COMP(sync_time);
+	CHECKPOINTER_COMP(buffers_written);
 #undef CHECKPOINTER_COMP
 }
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 998c69e241c..28ee97968b8 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1182,21 +1182,21 @@ PG_STAT_GET_DBENTRY_FLOAT8_MS(idle_in_transaction_time)
 PG_STAT_GET_DBENTRY_FLOAT8_MS(session_time)
 
 Datum
-pg_stat_get_bgwriter_timed_checkpoints(PG_FUNCTION_ARGS)
+pg_stat_get_checkpointer_num_timed(PG_FUNCTION_ARGS)
 {
-	PG_RETURN_INT64(pgstat_fetch_stat_checkpointer()->timed_checkpoints);
+	PG_RETURN_INT64(pgstat_fetch_stat_checkpointer()->num_timed);
 }
 
 Datum
-pg_stat_get_bgwriter_requested_checkpoints(PG_FUNCTION_ARGS)
+pg_stat_get_checkpointer_num_requested(PG_FUNCTION_ARGS)
 {
-	PG_RETURN_INT64(pgstat_fetch_stat_checkpointer()->requested_checkpoints);
+	PG_RETURN_INT64(pgstat_fetch_stat_checkpointer()->num_requested);
 }
 
 Datum
-pg_stat_get_bgwriter_buf_written_checkpoints(PG_FUNCTION_ARGS)
+pg_stat_get_checkpointer_buffers_written(PG_FUNCTION_ARGS)
 {
-	PG_RETURN_INT64(pgstat_fetch_stat_checkpointer()->buf_written_checkpoints);
+	PG_RETURN_INT64(pgstat_fetch_stat_checkpointer()->buffers_written);
 }
 
 Datum
@@ -1212,19 +1212,25 @@ pg_stat_get_bgwriter_maxwritten_clean(PG_FUNCTION_ARGS)
 }
 
 Datum
-pg_stat_get_checkpoint_write_time(PG_FUNCTION_ARGS)
+pg_stat_get_checkpointer_write_time(PG_FUNCTION_ARGS)
 {
 	/* time is already in msec, just convert to double for presentation */
 	PG_RETURN_FLOAT8((double)
-					 pgstat_fetch_stat_checkpointer()->checkpoint_write_time);
+					 pgstat_fetch_stat_checkpointer()->write_time);
 }
 
 Datum
-pg_stat_get_checkpoint_sync_time(PG_FUNCTION_ARGS)
+pg_stat_get_checkpointer_sync_time(PG_FUNCTION_ARGS)
 {
 	/* time is already in msec, just convert to double for presentation */
 	PG_RETURN_FLOAT8((double)
-					 pgstat_fetch_stat_checkpointer()->checkpoint_sync_time);
+					 pgstat_fetch_stat_checkpointer()->sync_time);
+}
+
+Datum
+pg_stat_get_checkpointer_stat_reset_time(PG_FUNCTION_ARGS)
+{
+	PG_RETURN_TIMESTAMPTZ(pgstat_fetch_stat_checkpointer()->stat_reset_timestamp);
 }
 
 Datum
@@ -1684,14 +1690,9 @@ pg_stat_reset_shared(PG_FUNCTION_ARGS)
 	if (strcmp(target, "archiver") == 0)
 		pgstat_reset_of_kind(PGSTAT_KIND_ARCHIVER);
 	else if (strcmp(target, "bgwriter") == 0)
-	{
-		/*
-		 * Historically checkpointer was part of bgwriter, continue to reset
-		 * both for now.
-		 */
 		pgstat_reset_of_kind(PGSTAT_KIND_BGWRITER);
+	else if (strcmp(target, "checkpointer") == 0)
 		pgstat_reset_of_kind(PGSTAT_KIND_CHECKPOINTER);
-	}
 	else if (strcmp(target, "io") == 0)
 		pgstat_reset_of_kind(PGSTAT_KIND_IO);
 	else if (strcmp(target, "recovery_prefetch") == 0)
@@ -1702,7 +1703,7 @@ pg_stat_reset_shared(PG_FUNCTION_ARGS)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("unrecognized reset target: \"%s\"", target),
-				 errhint("Target must be \"archiver\", \"bgwriter\", \"io\", \"recovery_prefetch\", or \"wal\".")));
+				 errhint("Target must be \"archiver\", \"bgwriter\", \"checkpointer\", \"io\", \"recovery_prefetch\", or \"wal\".")));
 
 	PG_RETURN_VOID();
 }