v12-0004-Remove-superfluous-bgwriter-stats.patch

From 5c3f382ba4eef310fc82b2b676029097eb99cd70 Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Wed, 29 Sep 2021 15:44:51 -0400
Subject: [PATCH v12 4/4] Remove superfluous bgwriter stats

Remove stats from pg_stat_bgwriter which are now more clearly expressed
in pg_stat_buffers.

TODO:
- make pg_stat_checkpointer view and move relevant stats into it
- add additional stats to pg_stat_bgwriter
---
 doc/src/sgml/monitoring.sgml          | 47 ---------------------------
 src/backend/catalog/system_views.sql  |  6 +---
 src/backend/postmaster/checkpointer.c | 26 ---------------
 src/backend/postmaster/pgstat.c       |  5 ---
 src/backend/storage/buffer/bufmgr.c   |  6 ----
 src/backend/utils/adt/pgstatfuncs.c   | 30 -----------------
 src/include/catalog/pg_proc.dat       | 22 -------------
 src/include/pgstat.h                  | 10 ------
 src/test/regress/expected/rules.out   |  5 ---
 9 files changed, 1 insertion(+), 156 deletions(-)

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 75753c3339..5852c45246 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3416,24 +3416,6 @@ 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_checkpoint</structfield> <type>bigint</type>
-      </para>
-      <para>
-       Number of buffers written during checkpoints
-      </para></entry>
-     </row>
-
-     <row>
-      <entry role="catalog_table_entry"><para role="column_definition">
-       <structfield>buffers_clean</structfield> <type>bigint</type>
-      </para>
-      <para>
-       Number of buffers written by the background writer
-      </para></entry>
-     </row>
-
      <row>
       <entry role="catalog_table_entry"><para role="column_definition">
        <structfield>maxwritten_clean</structfield> <type>bigint</type>
@@ -3444,35 +3426,6 @@ 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 30280d520b..c45c261f4b 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1058,18 +1058,14 @@ CREATE VIEW pg_stat_archiver AS
         s.stats_reset
     FROM pg_stat_get_archiver() s;
 
+-- TODO: make separate pg_stat_checkpointer view
 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_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_buffers AS
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index 931bdcaa59..712c878f1c 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_inc_buffer_access_type(BA_Fsync, Buf_Shared);
 		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 3673b34f50..f85e508689 100644
--- a/src/backend/postmaster/pgstat.c
+++ b/src/backend/postmaster/pgstat.c
@@ -5611,9 +5611,7 @@ pgstat_recv_archiver(PgStat_MsgArchiver *msg, int len)
 static void
 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;
 }
 
 /* ----------
@@ -5629,9 +5627,6 @@ pgstat_recv_checkpointer(PgStat_MsgCheckpointer *msg, int len)
 	globalStats.checkpointer.requested_checkpoints += msg->m_requested_checkpoints;
 	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 58bf60425b..f69dbe38b8 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -2166,7 +2166,6 @@ BufferSync(int flags)
 			if (SyncOneBuffer(buf_id, false, &wb_context) & BUF_WRITTEN)
 			{
 				TRACE_POSTGRESQL_BUFFER_SYNC_WRITTEN(buf_id);
-				PendingCheckpointerStats.m_buf_written_checkpoints++;
 				num_written++;
 			}
 		}
@@ -2275,9 +2274,6 @@ 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
@@ -2474,8 +2470,6 @@ BgBufferSync(WritebackContext *wb_context)
 			reusable_buffers++;
 	}
 
-	PendingBgWriterStats.m_buf_written_clean += num_written;
-
 #ifdef BGW_DEBUG
 	elog(DEBUG1, "bgwriter: recent_alloc=%u smoothed=%.2f delta=%ld ahead=%d density=%.2f reusable_est=%d upcoming_est=%d scanned=%d wrote=%d reusable=%d",
 		 recent_alloc, smoothed_alloc, strategy_delta, bufs_ahead,
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 674a2167ec..cf2998514e 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1723,18 +1723,6 @@ pg_stat_get_bgwriter_requested_checkpoints(PG_FUNCTION_ARGS)
 	PG_RETURN_INT64(pgstat_fetch_stat_checkpointer()->requested_checkpoints);
 }
 
-Datum
-pg_stat_get_bgwriter_buf_written_checkpoints(PG_FUNCTION_ARGS)
-{
-	PG_RETURN_INT64(pgstat_fetch_stat_checkpointer()->buf_written_checkpoints);
-}
-
-Datum
-pg_stat_get_bgwriter_buf_written_clean(PG_FUNCTION_ARGS)
-{
-	PG_RETURN_INT64(pgstat_fetch_stat_bgwriter()->buf_written_clean);
-}
-
 Datum
 pg_stat_get_bgwriter_maxwritten_clean(PG_FUNCTION_ARGS)
 {
@@ -1763,24 +1751,6 @@ 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_buffers_accesses(PG_FUNCTION_ARGS)
 {
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 54661e2b5f..02f624c18c 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5600,16 +5600,6 @@
   proname => 'pg_stat_get_bgwriter_requested_checkpoints', provolatile => 's',
   proparallel => 'r', prorettype => 'int8', proargtypes => '',
   prosrc => 'pg_stat_get_bgwriter_requested_checkpoints' },
-{ oid => '2771',
-  descr => 'statistics: number of buffers written by the bgwriter during checkpoints',
-  proname => 'pg_stat_get_bgwriter_buf_written_checkpoints', provolatile => 's',
-  proparallel => 'r', prorettype => 'int8', proargtypes => '',
-  prosrc => 'pg_stat_get_bgwriter_buf_written_checkpoints' },
-{ oid => '2772',
-  descr => 'statistics: number of buffers written by the bgwriter for cleaning dirty buffers',
-  proname => 'pg_stat_get_bgwriter_buf_written_clean', provolatile => 's',
-  proparallel => 'r', prorettype => 'int8', proargtypes => '',
-  prosrc => 'pg_stat_get_bgwriter_buf_written_clean' },
 { oid => '2773',
   descr => 'statistics: number of times the bgwriter stopped processing when it had written too many buffers while cleaning',
   proname => 'pg_stat_get_bgwriter_maxwritten_clean', provolatile => 's',
@@ -5629,18 +5619,6 @@
   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 various types of accesses of buffers done by each backend type',
   proname => 'pg_stat_get_buffers_accesses', provolatile => 's', proisstrict => 'f',
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index 2e3dfcc01d..02a9fff64e 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -505,9 +505,7 @@ typedef struct PgStat_MsgBgWriter
 {
 	PgStat_MsgHdr m_hdr;
 
-	PgStat_Counter m_buf_written_clean;
 	PgStat_Counter m_maxwritten_clean;
-	PgStat_Counter m_buf_alloc;
 } PgStat_MsgBgWriter;
 
 /* ----------
@@ -520,9 +518,6 @@ 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;
@@ -898,9 +893,7 @@ typedef struct PgStat_ArchiverStats
  */
 typedef struct PgStat_BgWriterStats
 {
-	PgStat_Counter buf_written_clean;
 	PgStat_Counter maxwritten_clean;
-	PgStat_Counter buf_alloc;
 	TimestampTz stat_reset_timestamp;
 } PgStat_BgWriterStats;
 
@@ -914,9 +907,6 @@ typedef struct PgStat_CheckpointerStats
 	PgStat_Counter requested_checkpoints;
 	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 9172b0fcd2..ac2f7cf61e 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1821,12 +1821,7 @@ pg_stat_bgwriter| SELECT pg_stat_get_bgwriter_timed_checkpoints() AS checkpoints
     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_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_buffers| SELECT b.backend_type,
     b.buffer_type,
-- 
2.27.0