v6-0002-Remove-superfluous-bgwriter-stats.patch

From 2887f6949fd4671e75062045f5d3e09621a273cd Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Thu, 2 Sep 2021 11:47:41 -0400
Subject: [PATCH v6 2/2] Remove superfluous bgwriter stats

Remove stats from pg_stat_bgwriter which are now more clearly expressed
in pg_stat_buffer_actions.
---
 doc/src/sgml/monitoring.sgml          | 29 ---------------------------
 src/backend/catalog/system_views.sql  |  3 ---
 src/backend/postmaster/checkpointer.c | 26 ------------------------
 src/backend/postmaster/pgstat.c       |  3 ---
 src/backend/storage/buffer/bufmgr.c   |  3 ---
 src/backend/utils/adt/pgstatfuncs.c   | 18 -----------------
 src/include/catalog/pg_proc.dat       | 12 -----------
 src/include/pgstat.h                  |  6 ------
 src/test/regress/expected/rules.out   |  3 ---
 9 files changed, 103 deletions(-)

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index edd19368be..087d3993c1 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3444,35 +3444,6 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
       </para></entry>
      </row>
 
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>buffers_backend</structfield> <type>bigint</type>
-      </para>
-      <para>
-       Number of buffers written directly by a backend
-      </para></entry>
-     </row>
-
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>buffers_backend_fsync</structfield> <type>bigint</type>
-      </para>
-      <para>
-       Number of times a backend had to execute its own
-       <function>fsync</function> call (normally the background writer handles those
-       even when the backend does its own write)
-      </para></entry>
-     </row>
-
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>buffers_alloc</structfield> <type>bigint</type>
-      </para>
-      <para>
-       Number of buffers allocated
-      </para></entry>
-     </row>
-
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>stats_reset</structfield> <type>timestamp with time zone</type>
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 7ba54d1119..f51e7938fc 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1067,9 +1067,6 @@ CREATE VIEW pg_stat_bgwriter AS
         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_written_backend() AS buffers_backend,
-        pg_stat_get_buf_fsync_backend() AS buffers_backend_fsync,
-        pg_stat_get_buf_alloc() AS buffers_alloc,
         pg_stat_get_bgwriter_stat_reset_time() AS stats_reset;
 
 CREATE VIEW pg_stat_buffer_actions AS
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index 23f2ffccd9..fca78fa4ef 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -90,17 +90,9 @@
  * requesting backends since the last checkpoint start.  The flags are
  * chosen so that OR'ing is the correct way to combine multiple requests.
  *
- * num_backend_writes is used to count the number of buffer writes performed
- * by user backend processes.  This counter should be wide enough that it
- * can't overflow during a single processing cycle.  num_backend_fsync
- * counts the subset of those writes that also had to do their own fsync,
- * because the checkpointer failed to absorb their request.
- *
  * The requests array holds fsync requests sent by backends and not yet
  * absorbed by the checkpointer.
  *
- * Unlike the checkpoint fields, num_backend_writes, num_backend_fsync, and
- * the requests fields are protected by CheckpointerCommLock.
  *----------
  */
 typedef struct
@@ -124,9 +116,6 @@ typedef struct
 	ConditionVariable start_cv; /* signaled when ckpt_started advances */
 	ConditionVariable done_cv;	/* signaled when ckpt_done advances */
 
-	uint32		num_backend_writes; /* counts user backend buffer writes */
-	uint32		num_backend_fsync;	/* counts user backend fsync calls */
-
 	int			num_requests;	/* current # of requests */
 	int			max_requests;	/* allocated array size */
 	CheckpointerRequest requests[FLEXIBLE_ARRAY_MEMBER];
@@ -1085,10 +1074,6 @@ ForwardSyncRequest(const FileTag *ftag, SyncRequestType type)
 
 	LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);
 
-	/* Count all backend writes regardless of if they fit in the queue */
-	if (!AmBackgroundWriterProcess())
-		CheckpointerShmem->num_backend_writes++;
-
 	/*
 	 * If the checkpointer isn't running or the request queue is full, the
 	 * backend will have to perform its own fsync request.  But before forcing
@@ -1102,8 +1087,6 @@ ForwardSyncRequest(const FileTag *ftag, SyncRequestType type)
 		 * Count the subset of writes where backends have to do their own
 		 * fsync
 		 */
-		if (!AmBackgroundWriterProcess())
-			CheckpointerShmem->num_backend_fsync++;
 		pgstat_increment_buffer_action(BA_Fsync);
 		LWLockRelease(CheckpointerCommLock);
 		return false;
@@ -1261,15 +1244,6 @@ AbsorbSyncRequests(void)
 
 	LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);
 
-	/* Transfer stats counts into pending pgstats message */
-	PendingCheckpointerStats.m_buf_written_backend
-		+= CheckpointerShmem->num_backend_writes;
-	PendingCheckpointerStats.m_buf_fsync_backend
-		+= CheckpointerShmem->num_backend_fsync;
-
-	CheckpointerShmem->num_backend_writes = 0;
-	CheckpointerShmem->num_backend_fsync = 0;
-
 	/*
 	 * We try to avoid holding the lock for a long time by copying the request
 	 * array, and processing the requests after releasing the lock.
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
index 244e5a7e44..74e1d32766 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -5426,7 +5426,6 @@ pgstat_recv_bgwriter(PgStat_MsgBgWriter *msg, int len)
 {
 	globalStats.bgwriter.buf_written_clean += msg->m_buf_written_clean;
 	globalStats.bgwriter.maxwritten_clean += msg->m_maxwritten_clean;
-	globalStats.bgwriter.buf_alloc += msg->m_buf_alloc;
 }
 
 /* ----------
@@ -5443,8 +5442,6 @@ pgstat_recv_checkpointer(PgStat_MsgCheckpointer *msg, int len)
 	globalStats.checkpointer.checkpoint_write_time += msg->m_checkpoint_write_time;
 	globalStats.checkpointer.checkpoint_sync_time += msg->m_checkpoint_sync_time;
 	globalStats.checkpointer.buf_written_checkpoints += msg->m_buf_written_checkpoints;
-	globalStats.checkpointer.buf_written_backend += msg->m_buf_written_backend;
-	globalStats.checkpointer.buf_fsync_backend += msg->m_buf_fsync_backend;
 }
 
 static void
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index ef83c576b0..b1bd528856 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -2267,9 +2267,6 @@ BgBufferSync(WritebackContext *wb_context)
 	 */
 	strategy_buf_id = StrategySyncStart(&strategy_passes, &recent_alloc);
 
-	/* Report buffer alloc counts to pgstat */
-	PendingBgWriterStats.m_buf_alloc += recent_alloc;
-
 	/*
 	 * If we're not running the LRU scan, just stop after doing the stats
 	 * stuff.  We mark the saved state invalid so that we can recover sanely
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 278257de80..2d8ab68a50 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1778,24 +1778,6 @@ pg_stat_get_bgwriter_stat_reset_time(PG_FUNCTION_ARGS)
 	PG_RETURN_TIMESTAMPTZ(pgstat_fetch_stat_bgwriter()->stat_reset_timestamp);
 }
 
-Datum
-pg_stat_get_buf_written_backend(PG_FUNCTION_ARGS)
-{
-	PG_RETURN_INT64(pgstat_fetch_stat_checkpointer()->buf_written_backend);
-}
-
-Datum
-pg_stat_get_buf_fsync_backend(PG_FUNCTION_ARGS)
-{
-	PG_RETURN_INT64(pgstat_fetch_stat_checkpointer()->buf_fsync_backend);
-}
-
-Datum
-pg_stat_get_buf_alloc(PG_FUNCTION_ARGS)
-{
-	PG_RETURN_INT64(pgstat_fetch_stat_bgwriter()->buf_alloc);
-}
-
 Datum
 pg_stat_get_buffer_actions(PG_FUNCTION_ARGS)
 {
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index ee3c11db06..26aa700ff8 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5629,18 +5629,6 @@
   proname => 'pg_stat_get_checkpoint_sync_time', provolatile => 's',
   proparallel => 'r', prorettype => 'float8', proargtypes => '',
   prosrc => 'pg_stat_get_checkpoint_sync_time' },
-{ oid => '2775', descr => 'statistics: number of buffers written by backends',
-  proname => 'pg_stat_get_buf_written_backend', provolatile => 's',
-  proparallel => 'r', prorettype => 'int8', proargtypes => '',
-  prosrc => 'pg_stat_get_buf_written_backend' },
-{ oid => '3063',
-  descr => 'statistics: number of backend buffer writes that did their own fsync',
-  proname => 'pg_stat_get_buf_fsync_backend', provolatile => 's',
-  proparallel => 'r', prorettype => 'int8', proargtypes => '',
-  prosrc => 'pg_stat_get_buf_fsync_backend' },
-{ oid => '2859', descr => 'statistics: number of buffer allocations',
-  proname => 'pg_stat_get_buf_alloc', provolatile => 's', proparallel => 'r',
-  prorettype => 'int8', proargtypes => '', prosrc => 'pg_stat_get_buf_alloc' },
 
 { oid => '8459', descr => 'statistics: counts of buffer actions taken by each backend type',
   proname => 'pg_stat_get_buffer_actions', provolatile => 's', proisstrict => 'f',
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 57c642aeca..22beef81ff 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -454,7 +454,6 @@ typedef struct PgStat_MsgBgWriter
 
 	PgStat_Counter m_buf_written_clean;
 	PgStat_Counter m_maxwritten_clean;
-	PgStat_Counter m_buf_alloc;
 } PgStat_MsgBgWriter;
 
 /* ----------
@@ -468,8 +467,6 @@ typedef struct PgStat_MsgCheckpointer
 	PgStat_Counter m_timed_checkpoints;
 	PgStat_Counter m_requested_checkpoints;
 	PgStat_Counter m_buf_written_checkpoints;
-	PgStat_Counter m_buf_written_backend;
-	PgStat_Counter m_buf_fsync_backend;
 	PgStat_Counter m_checkpoint_write_time; /* times in milliseconds */
 	PgStat_Counter m_checkpoint_sync_time;
 } PgStat_MsgCheckpointer;
@@ -852,7 +849,6 @@ typedef struct PgStat_BgWriterStats
 {
 	PgStat_Counter buf_written_clean;
 	PgStat_Counter maxwritten_clean;
-	PgStat_Counter buf_alloc;
 	TimestampTz stat_reset_timestamp;
 } PgStat_BgWriterStats;
 
@@ -867,8 +863,6 @@ typedef struct PgStat_CheckpointerStats
 	PgStat_Counter checkpoint_write_time;	/* times in milliseconds */
 	PgStat_Counter checkpoint_sync_time;
 	PgStat_Counter buf_written_checkpoints;
-	PgStat_Counter buf_written_backend;
-	PgStat_Counter buf_fsync_backend;
 } PgStat_CheckpointerStats;
 
 /*
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 5c5445bcd7..667f4444b3 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1824,9 +1824,6 @@ pg_stat_bgwriter| SELECT pg_stat_get_bgwriter_timed_checkpoints() AS checkpoints
     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_written_backend() AS buffers_backend,
-    pg_stat_get_buf_fsync_backend() AS buffers_backend_fsync,
-    pg_stat_get_buf_alloc() AS buffers_alloc,
     pg_stat_get_bgwriter_stat_reset_time() AS stats_reset;
 pg_stat_buffer_actions| SELECT b.backend_type,
     b.buffers_alloc,
-- 
2.32.0