v7-0001-Drop-buffers_backend-column-from-pg_stat_bgwriter.patch

From edb5ee994b179034273edd42c139aa57c9106922 Mon Sep 17 00:00:00 2001
From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Date: Fri, 10 Feb 2023 11:45:14 +0000
Subject: [PATCH v7] Drop buffers_backend column from pg_stat_bgwriter view

---
 doc/src/sgml/monitoring.sgml                  |  9 ---------
 src/backend/catalog/system_views.sql          |  1 -
 src/backend/postmaster/checkpointer.c         | 20 +++++--------------
 .../utils/activity/pgstat_checkpointer.c      |  2 --
 src/backend/utils/adt/pgstatfuncs.c           |  6 ------
 src/include/catalog/pg_proc.dat               |  4 ----
 src/include/pgstat.h                          |  1 -
 src/test/regress/expected/rules.out           |  1 -
 8 files changed, 5 insertions(+), 39 deletions(-)

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index b246ddc634..380085eedd 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3766,15 +3766,6 @@ 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>
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 8608e3fa5b..2b1b2bf7c3 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1112,7 +1112,6 @@ 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;
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index aaad5c5228..baadd08044 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -91,17 +91,15 @@
  * 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.
+ * num_backend_fsync counts the subset of buffer writes performed by user
+ * backend processes 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.
+ * Unlike the checkpoint fields, num_backend_fsync and the requests fields are
+ * protected by CheckpointerCommLock.
  *----------
  */
 typedef struct
@@ -125,7 +123,6 @@ 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 */
@@ -1096,10 +1093,6 @@ 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
@@ -1272,12 +1265,9 @@ AbsorbSyncRequests(void)
 	LWLockAcquire(CheckpointerCommLock, LW_EXCLUSIVE);
 
 	/* Transfer stats counts into pending pgstats message */
-	PendingCheckpointerStats.buf_written_backend
-		+= CheckpointerShmem->num_backend_writes;
 	PendingCheckpointerStats.buf_fsync_backend
 		+= CheckpointerShmem->num_backend_fsync;
 
-	CheckpointerShmem->num_backend_writes = 0;
 	CheckpointerShmem->num_backend_fsync = 0;
 
 	/*
diff --git a/src/backend/utils/activity/pgstat_checkpointer.c b/src/backend/utils/activity/pgstat_checkpointer.c
index 26dec112f6..a048205d6e 100644
--- a/src/backend/utils/activity/pgstat_checkpointer.c
+++ b/src/backend/utils/activity/pgstat_checkpointer.c
@@ -52,7 +52,6 @@ pgstat_report_checkpointer(void)
 	CHECKPOINTER_ACC(checkpoint_write_time);
 	CHECKPOINTER_ACC(checkpoint_sync_time);
 	CHECKPOINTER_ACC(buf_written_checkpoints);
-	CHECKPOINTER_ACC(buf_written_backend);
 	CHECKPOINTER_ACC(buf_fsync_backend);
 #undef CHECKPOINTER_ACC
 
@@ -120,7 +119,6 @@ pgstat_checkpointer_snapshot_cb(void)
 	CHECKPOINTER_COMP(checkpoint_write_time);
 	CHECKPOINTER_COMP(checkpoint_sync_time);
 	CHECKPOINTER_COMP(buf_written_checkpoints);
-	CHECKPOINTER_COMP(buf_written_backend);
 	CHECKPOINTER_COMP(buf_fsync_backend);
 #undef CHECKPOINTER_COMP
 }
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 924698e6ae..ce16884f1b 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1227,12 +1227,6 @@ 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)
 {
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index c0f2a8a77c..3188d9ee1f 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5704,10 +5704,6 @@
   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',
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index db9675884f..d1675909db 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -273,7 +273,6 @@ 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 e7a2f5856a..c98f9cd747 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1821,7 +1821,6 @@ 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;
-- 
2.34.1