pg_stat_io not tracking smgrwriteback() is confusing

From 6c5661ee5f0efbda9d246184f40cd799c21b5d2a Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Mon, 24 Apr 2023 18:21:54 -0400
Subject: [PATCH v1] Add writeback to pg_stat_io writes.

---
 src/backend/postmaster/bgwriter.c     |  4 ++--
 src/backend/storage/buffer/buf_init.c |  2 +-
 src/backend/storage/buffer/bufmgr.c   | 12 ++++++++++--
 src/include/storage/buf_internals.h   |  4 +++-
 4 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index caad642ec9..4c3540d6e1 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -129,7 +129,7 @@ BackgroundWriterMain(void)
 											 ALLOCSET_DEFAULT_SIZES);
 	MemoryContextSwitchTo(bgwriter_context);
 
-	WritebackContextInit(&wb_context, &bgwriter_flush_after);
+	WritebackContextInit(&wb_context, IOCONTEXT_NORMAL, &bgwriter_flush_after);
 
 	/*
 	 * If an exception is encountered, processing resumes here.
@@ -185,7 +185,7 @@ BackgroundWriterMain(void)
 		MemoryContextResetAndDeleteChildren(bgwriter_context);
 
 		/* re-initialize to avoid repeated errors causing problems */
-		WritebackContextInit(&wb_context, &bgwriter_flush_after);
+		WritebackContextInit(&wb_context, IOCONTEXT_NORMAL, &bgwriter_flush_after);
 
 		/* Now we can allow interrupts again */
 		RESUME_INTERRUPTS();
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index 0057443f0c..1d80532f3b 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -146,7 +146,7 @@ InitBufferPool(void)
 	StrategyInitialize(!foundDescs);
 
 	/* Initialize per-backend file flush context */
-	WritebackContextInit(&BackendWritebackContext,
+	WritebackContextInit(&BackendWritebackContext, IOCONTEXT_NORMAL,
 						 &backend_flush_after);
 }
 
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 1fa689052e..774dbadd08 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -1685,6 +1685,7 @@ again:
 		FlushBuffer(buf_hdr, NULL, IOOBJECT_RELATION, io_context);
 		LWLockRelease(content_lock);
 
+		BackendWritebackContext.io_context = io_context;
 		ScheduleBufferTagForWriteback(&BackendWritebackContext,
 									  &buf_hdr->tag);
 	}
@@ -2555,7 +2556,7 @@ BufferSync(int flags)
 	if (num_to_scan == 0)
 		return;					/* nothing to do */
 
-	WritebackContextInit(&wb_context, &checkpoint_flush_after);
+	WritebackContextInit(&wb_context, IOCONTEXT_NORMAL, &checkpoint_flush_after);
 
 	TRACE_POSTGRESQL_BUFFER_SYNC_START(NBuffers, num_to_scan);
 
@@ -5433,10 +5434,11 @@ ts_ckpt_progress_comparator(Datum a, Datum b, void *arg)
  * writeback control will be performed.
  */
 void
-WritebackContextInit(WritebackContext *context, int *max_pending)
+WritebackContextInit(WritebackContext *context, IOContext io_context, int *max_pending)
 {
 	Assert(*max_pending <= WRITEBACK_MAX_PENDING_FLUSHES);
 
+	context->io_context = io_context;
 	context->max_pending = max_pending;
 	context->nr_pending = 0;
 }
@@ -5491,6 +5493,7 @@ ScheduleBufferTagForWriteback(WritebackContext *context, BufferTag *tag)
 void
 IssuePendingWritebacks(WritebackContext *context)
 {
+	instr_time	io_start;
 	int			i;
 
 	if (context->nr_pending == 0)
@@ -5502,6 +5505,8 @@ IssuePendingWritebacks(WritebackContext *context)
 	 */
 	sort_pending_writebacks(context->pending_writebacks, context->nr_pending);
 
+	io_start = pgstat_prepare_io_time();
+
 	/*
 	 * Coalesce neighbouring writes, but nothing else. For that we iterate
 	 * through the, now sorted, array of pending flushes, and look forward to
@@ -5555,6 +5560,9 @@ IssuePendingWritebacks(WritebackContext *context)
 		smgrwriteback(reln, BufTagGetForkNum(&tag), tag.blockNum, nblocks);
 	}
 
+	pgstat_count_io_op_time(IOOBJECT_RELATION, context->io_context, IOOP_WRITE,
+			io_start, context->nr_pending);
+
 	context->nr_pending = 0;
 }
 
diff --git a/src/include/storage/buf_internals.h b/src/include/storage/buf_internals.h
index 136cf8fbaf..0d6e93ffad 100644
--- a/src/include/storage/buf_internals.h
+++ b/src/include/storage/buf_internals.h
@@ -295,6 +295,8 @@ typedef struct PendingWriteback
 /* struct forward declared in bufmgr.h */
 typedef struct WritebackContext
 {
+	IOContext io_context;
+
 	/* pointer to the max number of writeback requests to coalesce */
 	int		   *max_pending;
 
@@ -387,7 +389,7 @@ extern PGDLLIMPORT CkptSortItem *CkptBufferIds;
  * Internal buffer management routines
  */
 /* bufmgr.c */
-extern void WritebackContextInit(WritebackContext *context, int *max_pending);
+extern void WritebackContextInit(WritebackContext *context, IOContext io_context, int *max_pending);
 extern void IssuePendingWritebacks(WritebackContext *context);
 extern void ScheduleBufferTagForWriteback(WritebackContext *context, BufferTag *tag);
 
-- 
2.37.2

From b20765526e5c4bb5a82734ad9977552ebf9dad2f Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Mon, 24 Apr 2023 18:21:54 -0400
Subject: [PATCH v2] Add writeback to pg_stat_io

---
 doc/src/sgml/monitoring.sgml          | 24 ++++++++++++++++++++++++
 src/backend/catalog/system_views.sql  |  2 ++
 src/backend/postmaster/bgwriter.c     |  4 ++--
 src/backend/storage/buffer/buf_init.c |  2 +-
 src/backend/storage/buffer/bufmgr.c   | 12 ++++++++++--
 src/backend/utils/adt/pgstatfuncs.c   |  5 +++++
 src/include/catalog/pg_proc.dat       |  6 +++---
 src/include/pgstat.h                  |  3 ++-
 src/include/storage/buf_internals.h   |  4 +++-
 src/test/regress/expected/rules.out   |  4 +++-
 10 files changed, 55 insertions(+), 11 deletions(-)

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 99f7f95c39..62572327cf 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3867,6 +3867,30 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
       </entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry">
+       <para role="column_definition">
+        <structfield>writebacks</structfield> <type>bigint</type>
+       </para>
+       <para>
+        Number of writeback operations, each of the size specified in
+        <varname>op_bytes</varname>.
+       </para>
+      </entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry">
+       <para role="column_definition">
+        <structfield>writeback_time</structfield> <type>double precision</type>
+       </para>
+       <para>
+        Time spent in writeback operations in milliseconds (if
+        <xref linkend="guc-track-io-timing"/> is enabled, otherwise zero)
+       </para>
+      </entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry">
        <para role="column_definition">
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 48aacf66ee..d0c932ad0e 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1131,6 +1131,8 @@ SELECT
        b.read_time,
        b.writes,
        b.write_time,
+       b.writebacks,
+       b.writeback_time,
        b.extends,
        b.extend_time,
        b.op_bytes,
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index caad642ec9..4c3540d6e1 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -129,7 +129,7 @@ BackgroundWriterMain(void)
 											 ALLOCSET_DEFAULT_SIZES);
 	MemoryContextSwitchTo(bgwriter_context);
 
-	WritebackContextInit(&wb_context, &bgwriter_flush_after);
+	WritebackContextInit(&wb_context, IOCONTEXT_NORMAL, &bgwriter_flush_after);
 
 	/*
 	 * If an exception is encountered, processing resumes here.
@@ -185,7 +185,7 @@ BackgroundWriterMain(void)
 		MemoryContextResetAndDeleteChildren(bgwriter_context);
 
 		/* re-initialize to avoid repeated errors causing problems */
-		WritebackContextInit(&wb_context, &bgwriter_flush_after);
+		WritebackContextInit(&wb_context, IOCONTEXT_NORMAL, &bgwriter_flush_after);
 
 		/* Now we can allow interrupts again */
 		RESUME_INTERRUPTS();
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index 0057443f0c..1d80532f3b 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -146,7 +146,7 @@ InitBufferPool(void)
 	StrategyInitialize(!foundDescs);
 
 	/* Initialize per-backend file flush context */
-	WritebackContextInit(&BackendWritebackContext,
+	WritebackContextInit(&BackendWritebackContext, IOCONTEXT_NORMAL,
 						 &backend_flush_after);
 }
 
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 1fa689052e..188e135feb 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -1685,6 +1685,7 @@ again:
 		FlushBuffer(buf_hdr, NULL, IOOBJECT_RELATION, io_context);
 		LWLockRelease(content_lock);
 
+		BackendWritebackContext.io_context = io_context;
 		ScheduleBufferTagForWriteback(&BackendWritebackContext,
 									  &buf_hdr->tag);
 	}
@@ -2555,7 +2556,7 @@ BufferSync(int flags)
 	if (num_to_scan == 0)
 		return;					/* nothing to do */
 
-	WritebackContextInit(&wb_context, &checkpoint_flush_after);
+	WritebackContextInit(&wb_context, IOCONTEXT_NORMAL, &checkpoint_flush_after);
 
 	TRACE_POSTGRESQL_BUFFER_SYNC_START(NBuffers, num_to_scan);
 
@@ -5433,10 +5434,11 @@ ts_ckpt_progress_comparator(Datum a, Datum b, void *arg)
  * writeback control will be performed.
  */
 void
-WritebackContextInit(WritebackContext *context, int *max_pending)
+WritebackContextInit(WritebackContext *context, IOContext io_context, int *max_pending)
 {
 	Assert(*max_pending <= WRITEBACK_MAX_PENDING_FLUSHES);
 
+	context->io_context = io_context;
 	context->max_pending = max_pending;
 	context->nr_pending = 0;
 }
@@ -5491,6 +5493,7 @@ ScheduleBufferTagForWriteback(WritebackContext *context, BufferTag *tag)
 void
 IssuePendingWritebacks(WritebackContext *context)
 {
+	instr_time	io_start;
 	int			i;
 
 	if (context->nr_pending == 0)
@@ -5502,6 +5505,8 @@ IssuePendingWritebacks(WritebackContext *context)
 	 */
 	sort_pending_writebacks(context->pending_writebacks, context->nr_pending);
 
+	io_start = pgstat_prepare_io_time();
+
 	/*
 	 * Coalesce neighbouring writes, but nothing else. For that we iterate
 	 * through the, now sorted, array of pending flushes, and look forward to
@@ -5555,6 +5560,9 @@ IssuePendingWritebacks(WritebackContext *context)
 		smgrwriteback(reln, BufTagGetForkNum(&tag), tag.blockNum, nblocks);
 	}
 
+	pgstat_count_io_op_time(IOOBJECT_RELATION, context->io_context, IOOP_WRITEBACK,
+							io_start, context->nr_pending);
+
 	context->nr_pending = 0;
 }
 
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 0d57b6a7c0..70da0a2de1 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1268,6 +1268,8 @@ typedef enum io_stat_col
 	IO_COL_READ_TIME,
 	IO_COL_WRITES,
 	IO_COL_WRITE_TIME,
+	IO_COL_WRITEBACKS,
+	IO_COL_WRITEBACK_TIME,
 	IO_COL_EXTENDS,
 	IO_COL_EXTEND_TIME,
 	IO_COL_CONVERSION,
@@ -1303,6 +1305,8 @@ pgstat_get_io_op_index(IOOp io_op)
 			return IO_COL_REUSES;
 		case IOOP_WRITE:
 			return IO_COL_WRITES;
+		case IOOP_WRITEBACK:
+			return IO_COL_WRITEBACKS;
 	}
 
 	elog(ERROR, "unrecognized IOOp value: %d", io_op);
@@ -1322,6 +1326,7 @@ pgstat_get_io_time_index(IOOp io_op)
 	{
 		case IOOP_READ:
 		case IOOP_WRITE:
+		case IOOP_WRITEBACK:
 		case IOOP_EXTEND:
 		case IOOP_FSYNC:
 			return pgstat_get_io_op_index(io_op) + 1;
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index b2bc81b15f..e766b9b600 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5760,9 +5760,9 @@
   proname => 'pg_stat_get_io', provolatile => 'v',
   prorows => '30', proretset => 't',
   proparallel => 'r', prorettype => 'record', proargtypes => '',
-  proallargtypes => '{text,text,text,int8,float8,int8,float8,int8,float8,int8,int8,int8,int8,int8,float8,timestamptz}',
-  proargmodes => '{o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}',
-  proargnames => '{backend_type,object,context,reads,read_time,writes,write_time,extends,extend_time,op_bytes,hits,evictions,reuses,fsyncs,fsync_time,stats_reset}',
+  proallargtypes => '{text,text,text,int8,float8,int8,float8,int8,float8,int8,float8,int8,int8,int8,int8,int8,float8,timestamptz}',
+  proargmodes => '{o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}',
+  proargnames => '{backend_type,object,context,reads,read_time,writes,write_time,writebacks,writeback_time,extends,extend_time,op_bytes,hits,evictions,reuses,fsyncs,fsync_time,stats_reset}',
   prosrc => 'pg_stat_get_io' },
 
 { oid => '1136', descr => 'statistics: information about WAL activity',
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index fff4ad5b6d..57a2c0866a 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -300,9 +300,10 @@ typedef enum IOOp
 	IOOP_READ,
 	IOOP_REUSE,
 	IOOP_WRITE,
+	IOOP_WRITEBACK,
 } IOOp;
 
-#define IOOP_NUM_TYPES (IOOP_WRITE + 1)
+#define IOOP_NUM_TYPES (IOOP_WRITEBACK + 1)
 
 typedef struct PgStat_BktypeIO
 {
diff --git a/src/include/storage/buf_internals.h b/src/include/storage/buf_internals.h
index 136cf8fbaf..331ca26ce3 100644
--- a/src/include/storage/buf_internals.h
+++ b/src/include/storage/buf_internals.h
@@ -295,6 +295,8 @@ typedef struct PendingWriteback
 /* struct forward declared in bufmgr.h */
 typedef struct WritebackContext
 {
+	IOContext	io_context;
+
 	/* pointer to the max number of writeback requests to coalesce */
 	int		   *max_pending;
 
@@ -387,7 +389,7 @@ extern PGDLLIMPORT CkptSortItem *CkptBufferIds;
  * Internal buffer management routines
  */
 /* bufmgr.c */
-extern void WritebackContextInit(WritebackContext *context, int *max_pending);
+extern void WritebackContextInit(WritebackContext *context, IOContext io_context, int *max_pending);
 extern void IssuePendingWritebacks(WritebackContext *context);
 extern void ScheduleBufferTagForWriteback(WritebackContext *context, BufferTag *tag);
 
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 69957687fe..0bd6db2bf8 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1887,6 +1887,8 @@ pg_stat_io| SELECT backend_type,
     read_time,
     writes,
     write_time,
+    writebacks,
+    writeback_time,
     extends,
     extend_time,
     op_bytes,
@@ -1896,7 +1898,7 @@ pg_stat_io| SELECT backend_type,
     fsyncs,
     fsync_time,
     stats_reset
-   FROM pg_stat_get_io() b(backend_type, object, context, reads, read_time, writes, write_time, extends, extend_time, op_bytes, hits, evictions, reuses, fsyncs, fsync_time, stats_reset);
+   FROM pg_stat_get_io() b(backend_type, object, context, reads, read_time, writes, write_time, writebacks, writeback_time, extends, extend_time, op_bytes, hits, evictions, reuses, fsyncs, fsync_time, stats_reset);
 pg_stat_progress_analyze| SELECT s.pid,
     s.datid,
     d.datname,
-- 
2.37.2

From 8db3a8319553777024379add76527b8a6908028b Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Mon, 24 Apr 2023 18:21:54 -0400
Subject: [PATCH v3] Add writeback to pg_stat_io

28e626bde00 added the notion of IOOps but neglected to include
writeback. With the addition of IO timing to pg_stat_io in ac8d53dae5,
the omission of writeback caused some confusion. Checkpointer write
timing in pg_stat_io often differed greatly from the write timing
written to the log. To fix this, add IOOp IOOP_WRITEBACK and track
writebacks and writeback timing in pg_stat_io.

Discussion: https://postgr.es/m/20230419172326.dhgyo4wrrhulovt6%40awork3.anarazel.de
---
 doc/src/sgml/monitoring.sgml          | 27 +++++++++++++++++++++++++++
 src/backend/catalog/system_views.sql  |  2 ++
 src/backend/postmaster/bgwriter.c     | 10 ++++++++--
 src/backend/storage/buffer/buf_init.c | 11 ++++++++---
 src/backend/storage/buffer/bufmgr.c   | 20 ++++++++++++++++++--
 src/backend/utils/adt/pgstatfuncs.c   |  5 +++++
 src/include/catalog/pg_proc.dat       |  6 +++---
 src/include/pgstat.h                  |  3 ++-
 src/include/storage/buf_internals.h   |  6 +++++-
 src/test/regress/expected/rules.out   |  4 +++-
 src/test/regress/expected/stats.out   |  4 ++--
 src/test/regress/sql/stats.sql        |  4 ++--
 12 files changed, 85 insertions(+), 17 deletions(-)

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 99f7f95c39..d6062b3d89 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3867,6 +3867,33 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
       </entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry">
+       <para role="column_definition">
+        <structfield>writebacks</structfield> <type>bigint</type>
+       </para>
+       <para>
+        Number of units of size <varname>op_bytes</varname> which the backend
+        requested the kernel write out to permanent storage.
+       </para>
+      </entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry">
+       <para role="column_definition">
+        <structfield>writeback_time</structfield> <type>double precision</type>
+       </para>
+       <para>
+        Time spent in writeback operations in milliseconds (if
+        <xref linkend="guc-track-io-timing"/> is enabled, otherwise zero). This
+        does not necessarily count the time spent by the kernel writing the
+        data out. The backend will initiate write-out of the dirty pages and
+        wait only if the request queue is full.
+       </para>
+      </entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry">
        <para role="column_definition">
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 48aacf66ee..d0c932ad0e 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1131,6 +1131,8 @@ SELECT
        b.read_time,
        b.writes,
        b.write_time,
+       b.writebacks,
+       b.writeback_time,
        b.extends,
        b.extend_time,
        b.op_bytes,
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index caad642ec9..dbf866f262 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -129,7 +129,12 @@ BackgroundWriterMain(void)
 											 ALLOCSET_DEFAULT_SIZES);
 	MemoryContextSwitchTo(bgwriter_context);
 
-	WritebackContextInit(&wb_context, &bgwriter_flush_after);
+	/*
+	 * bgwriter will only request writeback for permanent relations in
+	 * IOCONTEXT_NORMAL.
+	 */
+	WritebackContextInit(&wb_context, IOOBJECT_RELATION, IOCONTEXT_NORMAL,
+						 &bgwriter_flush_after);
 
 	/*
 	 * If an exception is encountered, processing resumes here.
@@ -185,7 +190,8 @@ BackgroundWriterMain(void)
 		MemoryContextResetAndDeleteChildren(bgwriter_context);
 
 		/* re-initialize to avoid repeated errors causing problems */
-		WritebackContextInit(&wb_context, &bgwriter_flush_after);
+		WritebackContextInit(&wb_context, IOOBJECT_RELATION, IOCONTEXT_NORMAL,
+							 &bgwriter_flush_after);
 
 		/* Now we can allow interrupts again */
 		RESUME_INTERRUPTS();
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index 0057443f0c..b050e3c2aa 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -145,9 +145,14 @@ InitBufferPool(void)
 	/* Init other shared buffer-management stuff */
 	StrategyInitialize(!foundDescs);
 
-	/* Initialize per-backend file flush context */
-	WritebackContextInit(&BackendWritebackContext,
-						 &backend_flush_after);
+	/*
+	 * Initialize per-backend file flush context. IOObject is initialized to
+	 * IOOBJECT_RELATION and IOContext to IOCONTEXT_NORMAL since these are the
+	 * most likely targets for writeback. The backend can overwrite these as
+	 * appropriate.
+	 */
+	WritebackContextInit(&BackendWritebackContext, IOOBJECT_RELATION,
+						 IOCONTEXT_NORMAL, &backend_flush_after);
 }
 
 /*
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 1fa689052e..116910cdfe 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -1685,6 +1685,8 @@ again:
 		FlushBuffer(buf_hdr, NULL, IOOBJECT_RELATION, io_context);
 		LWLockRelease(content_lock);
 
+		BackendWritebackContext.io_object = IOOBJECT_RELATION;
+		BackendWritebackContext.io_context = io_context;
 		ScheduleBufferTagForWriteback(&BackendWritebackContext,
 									  &buf_hdr->tag);
 	}
@@ -2555,7 +2557,12 @@ BufferSync(int flags)
 	if (num_to_scan == 0)
 		return;					/* nothing to do */
 
-	WritebackContextInit(&wb_context, &checkpoint_flush_after);
+	/*
+	 * Checkpointer will only request writeback of permanent relations in
+	 * IOCONTEXT_NORMAL.
+	 */
+	WritebackContextInit(&wb_context, IOOBJECT_RELATION, IOCONTEXT_NORMAL,
+						 &checkpoint_flush_after);
 
 	TRACE_POSTGRESQL_BUFFER_SYNC_START(NBuffers, num_to_scan);
 
@@ -5433,10 +5440,13 @@ ts_ckpt_progress_comparator(Datum a, Datum b, void *arg)
  * writeback control will be performed.
  */
 void
-WritebackContextInit(WritebackContext *context, int *max_pending)
+WritebackContextInit(WritebackContext *context, IOObject io_object,
+					 IOContext io_context, int *max_pending)
 {
 	Assert(*max_pending <= WRITEBACK_MAX_PENDING_FLUSHES);
 
+	context->io_object = io_object;
+	context->io_context = io_context;
 	context->max_pending = max_pending;
 	context->nr_pending = 0;
 }
@@ -5491,6 +5501,7 @@ ScheduleBufferTagForWriteback(WritebackContext *context, BufferTag *tag)
 void
 IssuePendingWritebacks(WritebackContext *context)
 {
+	instr_time	io_start;
 	int			i;
 
 	if (context->nr_pending == 0)
@@ -5502,6 +5513,8 @@ IssuePendingWritebacks(WritebackContext *context)
 	 */
 	sort_pending_writebacks(context->pending_writebacks, context->nr_pending);
 
+	io_start = pgstat_prepare_io_time();
+
 	/*
 	 * Coalesce neighbouring writes, but nothing else. For that we iterate
 	 * through the, now sorted, array of pending flushes, and look forward to
@@ -5555,6 +5568,9 @@ IssuePendingWritebacks(WritebackContext *context)
 		smgrwriteback(reln, BufTagGetForkNum(&tag), tag.blockNum, nblocks);
 	}
 
+	pgstat_count_io_op_time(context->io_object, context->io_context,
+							IOOP_WRITEBACK, io_start, context->nr_pending);
+
 	context->nr_pending = 0;
 }
 
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 0d57b6a7c0..70da0a2de1 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1268,6 +1268,8 @@ typedef enum io_stat_col
 	IO_COL_READ_TIME,
 	IO_COL_WRITES,
 	IO_COL_WRITE_TIME,
+	IO_COL_WRITEBACKS,
+	IO_COL_WRITEBACK_TIME,
 	IO_COL_EXTENDS,
 	IO_COL_EXTEND_TIME,
 	IO_COL_CONVERSION,
@@ -1303,6 +1305,8 @@ pgstat_get_io_op_index(IOOp io_op)
 			return IO_COL_REUSES;
 		case IOOP_WRITE:
 			return IO_COL_WRITES;
+		case IOOP_WRITEBACK:
+			return IO_COL_WRITEBACKS;
 	}
 
 	elog(ERROR, "unrecognized IOOp value: %d", io_op);
@@ -1322,6 +1326,7 @@ pgstat_get_io_time_index(IOOp io_op)
 	{
 		case IOOP_READ:
 		case IOOP_WRITE:
+		case IOOP_WRITEBACK:
 		case IOOP_EXTEND:
 		case IOOP_FSYNC:
 			return pgstat_get_io_op_index(io_op) + 1;
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index b2bc81b15f..e766b9b600 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5760,9 +5760,9 @@
   proname => 'pg_stat_get_io', provolatile => 'v',
   prorows => '30', proretset => 't',
   proparallel => 'r', prorettype => 'record', proargtypes => '',
-  proallargtypes => '{text,text,text,int8,float8,int8,float8,int8,float8,int8,int8,int8,int8,int8,float8,timestamptz}',
-  proargmodes => '{o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}',
-  proargnames => '{backend_type,object,context,reads,read_time,writes,write_time,extends,extend_time,op_bytes,hits,evictions,reuses,fsyncs,fsync_time,stats_reset}',
+  proallargtypes => '{text,text,text,int8,float8,int8,float8,int8,float8,int8,float8,int8,int8,int8,int8,int8,float8,timestamptz}',
+  proargmodes => '{o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}',
+  proargnames => '{backend_type,object,context,reads,read_time,writes,write_time,writebacks,writeback_time,extends,extend_time,op_bytes,hits,evictions,reuses,fsyncs,fsync_time,stats_reset}',
   prosrc => 'pg_stat_get_io' },
 
 { oid => '1136', descr => 'statistics: information about WAL activity',
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index fff4ad5b6d..57a2c0866a 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -300,9 +300,10 @@ typedef enum IOOp
 	IOOP_READ,
 	IOOP_REUSE,
 	IOOP_WRITE,
+	IOOP_WRITEBACK,
 } IOOp;
 
-#define IOOP_NUM_TYPES (IOOP_WRITE + 1)
+#define IOOP_NUM_TYPES (IOOP_WRITEBACK + 1)
 
 typedef struct PgStat_BktypeIO
 {
diff --git a/src/include/storage/buf_internals.h b/src/include/storage/buf_internals.h
index 136cf8fbaf..0921710605 100644
--- a/src/include/storage/buf_internals.h
+++ b/src/include/storage/buf_internals.h
@@ -295,6 +295,9 @@ typedef struct PendingWriteback
 /* struct forward declared in bufmgr.h */
 typedef struct WritebackContext
 {
+	IOObject	io_object;
+	IOContext	io_context;
+
 	/* pointer to the max number of writeback requests to coalesce */
 	int		   *max_pending;
 
@@ -387,7 +390,8 @@ extern PGDLLIMPORT CkptSortItem *CkptBufferIds;
  * Internal buffer management routines
  */
 /* bufmgr.c */
-extern void WritebackContextInit(WritebackContext *context, int *max_pending);
+extern void WritebackContextInit(WritebackContext *context, IOObject io_object,
+								 IOContext io_context, int *max_pending);
 extern void IssuePendingWritebacks(WritebackContext *context);
 extern void ScheduleBufferTagForWriteback(WritebackContext *context, BufferTag *tag);
 
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 69957687fe..0bd6db2bf8 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1887,6 +1887,8 @@ pg_stat_io| SELECT backend_type,
     read_time,
     writes,
     write_time,
+    writebacks,
+    writeback_time,
     extends,
     extend_time,
     op_bytes,
@@ -1896,7 +1898,7 @@ pg_stat_io| SELECT backend_type,
     fsyncs,
     fsync_time,
     stats_reset
-   FROM pg_stat_get_io() b(backend_type, object, context, reads, read_time, writes, write_time, extends, extend_time, op_bytes, hits, evictions, reuses, fsyncs, fsync_time, stats_reset);
+   FROM pg_stat_get_io() b(backend_type, object, context, reads, read_time, writes, write_time, writebacks, writeback_time, extends, extend_time, op_bytes, hits, evictions, reuses, fsyncs, fsync_time, stats_reset);
 pg_stat_progress_analyze| SELECT s.pid,
     s.datid,
     d.datname,
diff --git a/src/test/regress/expected/stats.out b/src/test/regress/expected/stats.out
index 813d6d39ea..26ff27911a 100644
--- a/src/test/regress/expected/stats.out
+++ b/src/test/regress/expected/stats.out
@@ -1384,7 +1384,7 @@ SELECT pg_stat_have_stats('io', 0, 0);
  t
 (1 row)
 
-SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(hits) AS io_stats_pre_reset
+SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(writebacks) + sum(hits) AS io_stats_pre_reset
   FROM pg_stat_io \gset
 SELECT pg_stat_reset_shared('io');
  pg_stat_reset_shared 
@@ -1392,7 +1392,7 @@ SELECT pg_stat_reset_shared('io');
  
 (1 row)
 
-SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(hits) AS io_stats_post_reset
+SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(writebacks) + sum(hits) AS io_stats_post_reset
   FROM pg_stat_io \gset
 SELECT :io_stats_post_reset < :io_stats_pre_reset;
  ?column? 
diff --git a/src/test/regress/sql/stats.sql b/src/test/regress/sql/stats.sql
index 99a28bb79c..257e91d10d 100644
--- a/src/test/regress/sql/stats.sql
+++ b/src/test/regress/sql/stats.sql
@@ -694,10 +694,10 @@ SELECT :io_sum_bulkwrite_strategy_extends_after > :io_sum_bulkwrite_strategy_ext
 
 -- Test IO stats reset
 SELECT pg_stat_have_stats('io', 0, 0);
-SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(hits) AS io_stats_pre_reset
+SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(writebacks) + sum(hits) AS io_stats_pre_reset
   FROM pg_stat_io \gset
 SELECT pg_stat_reset_shared('io');
-SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(hits) AS io_stats_post_reset
+SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(writebacks) + sum(hits) AS io_stats_post_reset
   FROM pg_stat_io \gset
 SELECT :io_stats_post_reset < :io_stats_pre_reset;
 
-- 
2.37.2

From 7cdd6fc78ed82180a705ab9667714f80d08c5f7d Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Mon, 24 Apr 2023 18:21:54 -0400
Subject: [PATCH v4] Add writeback to pg_stat_io

28e626bde00 added the notion of IOOps but neglected to include
writeback. With the addition of IO timing to pg_stat_io in ac8d53dae5,
the omission of writeback caused some confusion. Checkpointer write
timing in pg_stat_io often differed greatly from the write timing
written to the log. To fix this, add IOOp IOOP_WRITEBACK and track
writebacks and writeback timing in pg_stat_io.

Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reported-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/20230419172326.dhgyo4wrrhulovt6%40awork3.anarazel.de
---
 doc/src/sgml/monitoring.sgml          | 26 ++++++++++++++++++++++++++
 src/backend/catalog/system_views.sql  |  2 ++
 src/backend/postmaster/bgwriter.c     | 10 ++++++++--
 src/backend/storage/buffer/buf_init.c | 12 +++++++++---
 src/backend/storage/buffer/bufmgr.c   | 20 ++++++++++++++++++--
 src/backend/utils/adt/pgstatfuncs.c   |  5 +++++
 src/include/catalog/pg_proc.dat       |  6 +++---
 src/include/pgstat.h                  |  3 ++-
 src/include/storage/buf_internals.h   |  6 +++++-
 src/test/regress/expected/rules.out   |  4 +++-
 src/test/regress/expected/stats.out   |  4 ++--
 src/test/regress/sql/stats.sql        |  4 ++--
 12 files changed, 85 insertions(+), 17 deletions(-)

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 99f7f95c39..27b6f1a0a0 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3867,6 +3867,32 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
       </entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry">
+       <para role="column_definition">
+        <structfield>writebacks</structfield> <type>bigint</type>
+       </para>
+       <para>
+        Number of units of size <varname>op_bytes</varname> which the backend
+        requested the kernel write out to permanent storage.
+       </para>
+      </entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry">
+       <para role="column_definition">
+        <structfield>writeback_time</structfield> <type>double precision</type>
+       </para>
+       <para>
+        Time spent in writeback operations in milliseconds (if
+        <xref linkend="guc-track-io-timing"/> is enabled, otherwise zero). This
+        includes the time spent queueing write-out requests and, potentially,
+        the time spent to write out the dirty data.
+       </para>
+      </entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry">
        <para role="column_definition">
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 48aacf66ee..d0c932ad0e 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1131,6 +1131,8 @@ SELECT
        b.read_time,
        b.writes,
        b.write_time,
+       b.writebacks,
+       b.writeback_time,
        b.extends,
        b.extend_time,
        b.op_bytes,
diff --git a/src/backend/postmaster/bgwriter.c b/src/backend/postmaster/bgwriter.c
index caad642ec9..dbf866f262 100644
--- a/src/backend/postmaster/bgwriter.c
+++ b/src/backend/postmaster/bgwriter.c
@@ -129,7 +129,12 @@ BackgroundWriterMain(void)
 											 ALLOCSET_DEFAULT_SIZES);
 	MemoryContextSwitchTo(bgwriter_context);
 
-	WritebackContextInit(&wb_context, &bgwriter_flush_after);
+	/*
+	 * bgwriter will only request writeback for permanent relations in
+	 * IOCONTEXT_NORMAL.
+	 */
+	WritebackContextInit(&wb_context, IOOBJECT_RELATION, IOCONTEXT_NORMAL,
+						 &bgwriter_flush_after);
 
 	/*
 	 * If an exception is encountered, processing resumes here.
@@ -185,7 +190,8 @@ BackgroundWriterMain(void)
 		MemoryContextResetAndDeleteChildren(bgwriter_context);
 
 		/* re-initialize to avoid repeated errors causing problems */
-		WritebackContextInit(&wb_context, &bgwriter_flush_after);
+		WritebackContextInit(&wb_context, IOOBJECT_RELATION, IOCONTEXT_NORMAL,
+							 &bgwriter_flush_after);
 
 		/* Now we can allow interrupts again */
 		RESUME_INTERRUPTS();
diff --git a/src/backend/storage/buffer/buf_init.c b/src/backend/storage/buffer/buf_init.c
index 0057443f0c..a7182fe95a 100644
--- a/src/backend/storage/buffer/buf_init.c
+++ b/src/backend/storage/buffer/buf_init.c
@@ -145,9 +145,15 @@ InitBufferPool(void)
 	/* Init other shared buffer-management stuff */
 	StrategyInitialize(!foundDescs);
 
-	/* Initialize per-backend file flush context */
-	WritebackContextInit(&BackendWritebackContext,
-						 &backend_flush_after);
+	/*
+	 * Initialize per-backend file flush context. IOContext is initialized to
+	 * IOCONTEXT_NORMAL because this is the most common context. IOObject is
+	 * initialized to IOOBJECT_RELATION because writeback is currently only
+	 * requested for permanent relations in shared buffers. The backend can
+	 * overwrite these as appropriate.
+	 */
+	WritebackContextInit(&BackendWritebackContext, IOOBJECT_RELATION,
+						 IOCONTEXT_NORMAL, &backend_flush_after);
 }
 
 /*
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 1fa689052e..116910cdfe 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -1685,6 +1685,8 @@ again:
 		FlushBuffer(buf_hdr, NULL, IOOBJECT_RELATION, io_context);
 		LWLockRelease(content_lock);
 
+		BackendWritebackContext.io_object = IOOBJECT_RELATION;
+		BackendWritebackContext.io_context = io_context;
 		ScheduleBufferTagForWriteback(&BackendWritebackContext,
 									  &buf_hdr->tag);
 	}
@@ -2555,7 +2557,12 @@ BufferSync(int flags)
 	if (num_to_scan == 0)
 		return;					/* nothing to do */
 
-	WritebackContextInit(&wb_context, &checkpoint_flush_after);
+	/*
+	 * Checkpointer will only request writeback of permanent relations in
+	 * IOCONTEXT_NORMAL.
+	 */
+	WritebackContextInit(&wb_context, IOOBJECT_RELATION, IOCONTEXT_NORMAL,
+						 &checkpoint_flush_after);
 
 	TRACE_POSTGRESQL_BUFFER_SYNC_START(NBuffers, num_to_scan);
 
@@ -5433,10 +5440,13 @@ ts_ckpt_progress_comparator(Datum a, Datum b, void *arg)
  * writeback control will be performed.
  */
 void
-WritebackContextInit(WritebackContext *context, int *max_pending)
+WritebackContextInit(WritebackContext *context, IOObject io_object,
+					 IOContext io_context, int *max_pending)
 {
 	Assert(*max_pending <= WRITEBACK_MAX_PENDING_FLUSHES);
 
+	context->io_object = io_object;
+	context->io_context = io_context;
 	context->max_pending = max_pending;
 	context->nr_pending = 0;
 }
@@ -5491,6 +5501,7 @@ ScheduleBufferTagForWriteback(WritebackContext *context, BufferTag *tag)
 void
 IssuePendingWritebacks(WritebackContext *context)
 {
+	instr_time	io_start;
 	int			i;
 
 	if (context->nr_pending == 0)
@@ -5502,6 +5513,8 @@ IssuePendingWritebacks(WritebackContext *context)
 	 */
 	sort_pending_writebacks(context->pending_writebacks, context->nr_pending);
 
+	io_start = pgstat_prepare_io_time();
+
 	/*
 	 * Coalesce neighbouring writes, but nothing else. For that we iterate
 	 * through the, now sorted, array of pending flushes, and look forward to
@@ -5555,6 +5568,9 @@ IssuePendingWritebacks(WritebackContext *context)
 		smgrwriteback(reln, BufTagGetForkNum(&tag), tag.blockNum, nblocks);
 	}
 
+	pgstat_count_io_op_time(context->io_object, context->io_context,
+							IOOP_WRITEBACK, io_start, context->nr_pending);
+
 	context->nr_pending = 0;
 }
 
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 0d57b6a7c0..70da0a2de1 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1268,6 +1268,8 @@ typedef enum io_stat_col
 	IO_COL_READ_TIME,
 	IO_COL_WRITES,
 	IO_COL_WRITE_TIME,
+	IO_COL_WRITEBACKS,
+	IO_COL_WRITEBACK_TIME,
 	IO_COL_EXTENDS,
 	IO_COL_EXTEND_TIME,
 	IO_COL_CONVERSION,
@@ -1303,6 +1305,8 @@ pgstat_get_io_op_index(IOOp io_op)
 			return IO_COL_REUSES;
 		case IOOP_WRITE:
 			return IO_COL_WRITES;
+		case IOOP_WRITEBACK:
+			return IO_COL_WRITEBACKS;
 	}
 
 	elog(ERROR, "unrecognized IOOp value: %d", io_op);
@@ -1322,6 +1326,7 @@ pgstat_get_io_time_index(IOOp io_op)
 	{
 		case IOOP_READ:
 		case IOOP_WRITE:
+		case IOOP_WRITEBACK:
 		case IOOP_EXTEND:
 		case IOOP_FSYNC:
 			return pgstat_get_io_op_index(io_op) + 1;
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index b2bc81b15f..e766b9b600 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5760,9 +5760,9 @@
   proname => 'pg_stat_get_io', provolatile => 'v',
   prorows => '30', proretset => 't',
   proparallel => 'r', prorettype => 'record', proargtypes => '',
-  proallargtypes => '{text,text,text,int8,float8,int8,float8,int8,float8,int8,int8,int8,int8,int8,float8,timestamptz}',
-  proargmodes => '{o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}',
-  proargnames => '{backend_type,object,context,reads,read_time,writes,write_time,extends,extend_time,op_bytes,hits,evictions,reuses,fsyncs,fsync_time,stats_reset}',
+  proallargtypes => '{text,text,text,int8,float8,int8,float8,int8,float8,int8,float8,int8,int8,int8,int8,int8,float8,timestamptz}',
+  proargmodes => '{o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}',
+  proargnames => '{backend_type,object,context,reads,read_time,writes,write_time,writebacks,writeback_time,extends,extend_time,op_bytes,hits,evictions,reuses,fsyncs,fsync_time,stats_reset}',
   prosrc => 'pg_stat_get_io' },
 
 { oid => '1136', descr => 'statistics: information about WAL activity',
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index fff4ad5b6d..57a2c0866a 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -300,9 +300,10 @@ typedef enum IOOp
 	IOOP_READ,
 	IOOP_REUSE,
 	IOOP_WRITE,
+	IOOP_WRITEBACK,
 } IOOp;
 
-#define IOOP_NUM_TYPES (IOOP_WRITE + 1)
+#define IOOP_NUM_TYPES (IOOP_WRITEBACK + 1)
 
 typedef struct PgStat_BktypeIO
 {
diff --git a/src/include/storage/buf_internals.h b/src/include/storage/buf_internals.h
index 136cf8fbaf..0921710605 100644
--- a/src/include/storage/buf_internals.h
+++ b/src/include/storage/buf_internals.h
@@ -295,6 +295,9 @@ typedef struct PendingWriteback
 /* struct forward declared in bufmgr.h */
 typedef struct WritebackContext
 {
+	IOObject	io_object;
+	IOContext	io_context;
+
 	/* pointer to the max number of writeback requests to coalesce */
 	int		   *max_pending;
 
@@ -387,7 +390,8 @@ extern PGDLLIMPORT CkptSortItem *CkptBufferIds;
  * Internal buffer management routines
  */
 /* bufmgr.c */
-extern void WritebackContextInit(WritebackContext *context, int *max_pending);
+extern void WritebackContextInit(WritebackContext *context, IOObject io_object,
+								 IOContext io_context, int *max_pending);
 extern void IssuePendingWritebacks(WritebackContext *context);
 extern void ScheduleBufferTagForWriteback(WritebackContext *context, BufferTag *tag);
 
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 69957687fe..0bd6db2bf8 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1887,6 +1887,8 @@ pg_stat_io| SELECT backend_type,
     read_time,
     writes,
     write_time,
+    writebacks,
+    writeback_time,
     extends,
     extend_time,
     op_bytes,
@@ -1896,7 +1898,7 @@ pg_stat_io| SELECT backend_type,
     fsyncs,
     fsync_time,
     stats_reset
-   FROM pg_stat_get_io() b(backend_type, object, context, reads, read_time, writes, write_time, extends, extend_time, op_bytes, hits, evictions, reuses, fsyncs, fsync_time, stats_reset);
+   FROM pg_stat_get_io() b(backend_type, object, context, reads, read_time, writes, write_time, writebacks, writeback_time, extends, extend_time, op_bytes, hits, evictions, reuses, fsyncs, fsync_time, stats_reset);
 pg_stat_progress_analyze| SELECT s.pid,
     s.datid,
     d.datname,
diff --git a/src/test/regress/expected/stats.out b/src/test/regress/expected/stats.out
index 813d6d39ea..26ff27911a 100644
--- a/src/test/regress/expected/stats.out
+++ b/src/test/regress/expected/stats.out
@@ -1384,7 +1384,7 @@ SELECT pg_stat_have_stats('io', 0, 0);
  t
 (1 row)
 
-SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(hits) AS io_stats_pre_reset
+SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(writebacks) + sum(hits) AS io_stats_pre_reset
   FROM pg_stat_io \gset
 SELECT pg_stat_reset_shared('io');
  pg_stat_reset_shared 
@@ -1392,7 +1392,7 @@ SELECT pg_stat_reset_shared('io');
  
 (1 row)
 
-SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(hits) AS io_stats_post_reset
+SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(writebacks) + sum(hits) AS io_stats_post_reset
   FROM pg_stat_io \gset
 SELECT :io_stats_post_reset < :io_stats_pre_reset;
  ?column? 
diff --git a/src/test/regress/sql/stats.sql b/src/test/regress/sql/stats.sql
index 99a28bb79c..257e91d10d 100644
--- a/src/test/regress/sql/stats.sql
+++ b/src/test/regress/sql/stats.sql
@@ -694,10 +694,10 @@ SELECT :io_sum_bulkwrite_strategy_extends_after > :io_sum_bulkwrite_strategy_ext
 
 -- Test IO stats reset
 SELECT pg_stat_have_stats('io', 0, 0);
-SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(hits) AS io_stats_pre_reset
+SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(writebacks) + sum(hits) AS io_stats_pre_reset
   FROM pg_stat_io \gset
 SELECT pg_stat_reset_shared('io');
-SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(hits) AS io_stats_post_reset
+SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(writebacks) + sum(hits) AS io_stats_post_reset
   FROM pg_stat_io \gset
 SELECT :io_stats_post_reset < :io_stats_pre_reset;
 
-- 
2.37.2

From 0ab9af06934ab551f2224493e913ae26000b3f87 Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Sat, 6 May 2023 12:24:28 -0400
Subject: [PATCH v5 1/3] BUFFER_USAGE_LIMIT reduces needed test table size

Using the minimum BUFFER_USAGE_LIMIT value, the VACUUM ring buffer is
smaller and we can make one of the pg_stat_io test tables smaller while
still causing reuses.
---
 src/test/regress/expected/stats.out | 6 ++++--
 src/test/regress/sql/stats.sql      | 6 ++++--
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/src/test/regress/expected/stats.out b/src/test/regress/expected/stats.out
index 813d6d39ea..d4e4889e7b 100644
--- a/src/test/regress/expected/stats.out
+++ b/src/test/regress/expected/stats.out
@@ -1337,11 +1337,13 @@ SET wal_skip_threshold = '1 kB';
 SELECT sum(reuses) AS reuses, sum(reads) AS reads
   FROM pg_stat_io WHERE context = 'vacuum' \gset io_sum_vac_strategy_before_
 CREATE TABLE test_io_vac_strategy(a int, b int) WITH (autovacuum_enabled = 'false');
-INSERT INTO test_io_vac_strategy SELECT i, i from generate_series(1, 8000)i;
+INSERT INTO test_io_vac_strategy SELECT i, i from generate_series(1, 4500)i;
 -- Ensure that the next VACUUM will need to perform IO by rewriting the table
 -- first with VACUUM (FULL).
 VACUUM (FULL) test_io_vac_strategy;
-VACUUM (PARALLEL 0) test_io_vac_strategy;
+-- Use the minimum BUFFER_USAGE_LIMIT to cause reuses with the smallest table
+-- possible.
+VACUUM (PARALLEL 0, BUFFER_USAGE_LIMIT 128) test_io_vac_strategy;
 SELECT pg_stat_force_next_flush();
  pg_stat_force_next_flush 
 --------------------------
diff --git a/src/test/regress/sql/stats.sql b/src/test/regress/sql/stats.sql
index 99a28bb79c..7ba341314f 100644
--- a/src/test/regress/sql/stats.sql
+++ b/src/test/regress/sql/stats.sql
@@ -670,11 +670,13 @@ SET wal_skip_threshold = '1 kB';
 SELECT sum(reuses) AS reuses, sum(reads) AS reads
   FROM pg_stat_io WHERE context = 'vacuum' \gset io_sum_vac_strategy_before_
 CREATE TABLE test_io_vac_strategy(a int, b int) WITH (autovacuum_enabled = 'false');
-INSERT INTO test_io_vac_strategy SELECT i, i from generate_series(1, 8000)i;
+INSERT INTO test_io_vac_strategy SELECT i, i from generate_series(1, 4500)i;
 -- Ensure that the next VACUUM will need to perform IO by rewriting the table
 -- first with VACUUM (FULL).
 VACUUM (FULL) test_io_vac_strategy;
-VACUUM (PARALLEL 0) test_io_vac_strategy;
+-- Use the minimum BUFFER_USAGE_LIMIT to cause reuses with the smallest table
+-- possible.
+VACUUM (PARALLEL 0, BUFFER_USAGE_LIMIT 128) test_io_vac_strategy;
 SELECT pg_stat_force_next_flush();
 SELECT sum(reuses) AS reuses, sum(reads) AS reads
   FROM pg_stat_io WHERE context = 'vacuum' \gset io_sum_vac_strategy_after_
-- 
2.37.2

From 87a9fa0da3895083d24bb2ee9a744a5afa11e5af Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Sat, 6 May 2023 11:11:04 -0400
Subject: [PATCH v5 2/3] Update parameter name context to wb_context

For clarity of review, renaming the function parameter "context" in
ScheduleBufferTagForWriteback() and IssuePendingWritebacks() to
"wb_context" is a separate commit. The next commit adds an "io_context"
parameter and "wb_context" makes it more clear which is which.
---
 src/backend/storage/buffer/bufmgr.c | 28 ++++++++++++++--------------
 src/include/storage/buf_internals.h |  4 ++--
 2 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 1fa689052e..041d5dc129 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -5445,7 +5445,7 @@ WritebackContextInit(WritebackContext *context, int *max_pending)
  * Add buffer to list of pending writeback requests.
  */
 void
-ScheduleBufferTagForWriteback(WritebackContext *context, BufferTag *tag)
+ScheduleBufferTagForWriteback(WritebackContext *wb_context, BufferTag *tag)
 {
 	PendingWriteback *pending;
 
@@ -5456,11 +5456,11 @@ ScheduleBufferTagForWriteback(WritebackContext *context, BufferTag *tag)
 	 * Add buffer to the pending writeback array, unless writeback control is
 	 * disabled.
 	 */
-	if (*context->max_pending > 0)
+	if (*wb_context->max_pending > 0)
 	{
-		Assert(*context->max_pending <= WRITEBACK_MAX_PENDING_FLUSHES);
+		Assert(*wb_context->max_pending <= WRITEBACK_MAX_PENDING_FLUSHES);
 
-		pending = &context->pending_writebacks[context->nr_pending++];
+		pending = &wb_context->pending_writebacks[wb_context->nr_pending++];
 
 		pending->tag = *tag;
 	}
@@ -5470,8 +5470,8 @@ ScheduleBufferTagForWriteback(WritebackContext *context, BufferTag *tag)
 	 * includes the case where previously an item has been added, but control
 	 * is now disabled.
 	 */
-	if (context->nr_pending >= *context->max_pending)
-		IssuePendingWritebacks(context);
+	if (wb_context->nr_pending >= *wb_context->max_pending)
+		IssuePendingWritebacks(wb_context);
 }
 
 #define ST_SORT sort_pending_writebacks
@@ -5489,25 +5489,25 @@ ScheduleBufferTagForWriteback(WritebackContext *context, BufferTag *tag)
  * error out - it's just a hint.
  */
 void
-IssuePendingWritebacks(WritebackContext *context)
+IssuePendingWritebacks(WritebackContext *wb_context)
 {
 	int			i;
 
-	if (context->nr_pending == 0)
+	if (wb_context->nr_pending == 0)
 		return;
 
 	/*
 	 * Executing the writes in-order can make them a lot faster, and allows to
 	 * merge writeback requests to consecutive blocks into larger writebacks.
 	 */
-	sort_pending_writebacks(context->pending_writebacks, context->nr_pending);
+	sort_pending_writebacks(wb_context->pending_writebacks, wb_context->nr_pending);
 
 	/*
 	 * Coalesce neighbouring writes, but nothing else. For that we iterate
 	 * through the, now sorted, array of pending flushes, and look forward to
 	 * find all neighbouring (or identical) writes.
 	 */
-	for (i = 0; i < context->nr_pending; i++)
+	for (i = 0; i < wb_context->nr_pending; i++)
 	{
 		PendingWriteback *cur;
 		PendingWriteback *next;
@@ -5517,7 +5517,7 @@ IssuePendingWritebacks(WritebackContext *context)
 		RelFileLocator currlocator;
 		Size		nblocks = 1;
 
-		cur = &context->pending_writebacks[i];
+		cur = &wb_context->pending_writebacks[i];
 		tag = cur->tag;
 		currlocator = BufTagGetRelFileLocator(&tag);
 
@@ -5525,10 +5525,10 @@ IssuePendingWritebacks(WritebackContext *context)
 		 * Peek ahead, into following writeback requests, to see if they can
 		 * be combined with the current one.
 		 */
-		for (ahead = 0; i + ahead + 1 < context->nr_pending; ahead++)
+		for (ahead = 0; i + ahead + 1 < wb_context->nr_pending; ahead++)
 		{
 
-			next = &context->pending_writebacks[i + ahead + 1];
+			next = &wb_context->pending_writebacks[i + ahead + 1];
 
 			/* different file, stop */
 			if (!RelFileLocatorEquals(currlocator,
@@ -5555,7 +5555,7 @@ IssuePendingWritebacks(WritebackContext *context)
 		smgrwriteback(reln, BufTagGetForkNum(&tag), tag.blockNum, nblocks);
 	}
 
-	context->nr_pending = 0;
+	wb_context->nr_pending = 0;
 }
 
 
diff --git a/src/include/storage/buf_internals.h b/src/include/storage/buf_internals.h
index 136cf8fbaf..f8ac811379 100644
--- a/src/include/storage/buf_internals.h
+++ b/src/include/storage/buf_internals.h
@@ -388,8 +388,8 @@ extern PGDLLIMPORT CkptSortItem *CkptBufferIds;
  */
 /* bufmgr.c */
 extern void WritebackContextInit(WritebackContext *context, int *max_pending);
-extern void IssuePendingWritebacks(WritebackContext *context);
-extern void ScheduleBufferTagForWriteback(WritebackContext *context, BufferTag *tag);
+extern void IssuePendingWritebacks(WritebackContext *wb_context);
+extern void ScheduleBufferTagForWriteback(WritebackContext *wb_context, BufferTag *tag);
 
 /* freelist.c */
 extern IOContext IOContextForStrategy(BufferAccessStrategy strategy);
-- 
2.37.2

From 8420944a3b57a292ce56f34a985498844e8dd3c1 Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Sat, 6 May 2023 11:16:58 -0400
Subject: [PATCH v5 3/3] Add writeback to pg_stat_io

28e626bde00 added the concept of IOOps but neglected to include
writeback operations. ac8d53dae5 added time spent doing these I/O
operations. Without counting writeback, checkpointer write timing in the
log often differed substantially from that in pg_stat_io. To fix this,
add IOOp IOOP_WRITEBACK and track writeback in pg_stat_io.

NOTE: Catalog version must be increased.

Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Reported-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/20230419172326.dhgyo4wrrhulovt6%40awork3.anarazel.de
---
 doc/src/sgml/monitoring.sgml           | 26 +++++++++++++++++++++
 src/backend/catalog/system_views.sql   |  2 ++
 src/backend/storage/buffer/bufmgr.c    | 32 ++++++++++++++++++++------
 src/backend/utils/activity/pgstat_io.c | 14 ++++++-----
 src/backend/utils/adt/pgstatfuncs.c    |  5 ++++
 src/include/catalog/pg_proc.dat        |  6 ++---
 src/include/pgstat.h                   |  3 ++-
 src/include/storage/buf_internals.h    |  5 ++--
 src/test/regress/expected/rules.out    |  4 +++-
 src/test/regress/expected/stats.out    |  4 ++--
 src/test/regress/sql/stats.sql         |  4 ++--
 11 files changed, 81 insertions(+), 24 deletions(-)

diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml
index 99f7f95c39..cf13ade205 100644
--- a/doc/src/sgml/monitoring.sgml
+++ b/doc/src/sgml/monitoring.sgml
@@ -3867,6 +3867,32 @@ SELECT pid, wait_event_type, wait_event FROM pg_stat_activity WHERE wait_event i
       </entry>
      </row>
 
+     <row>
+      <entry role="catalog_table_entry">
+       <para role="column_definition">
+        <structfield>writebacks</structfield> <type>bigint</type>
+       </para>
+       <para>
+        Number of units of size <varname>op_bytes</varname> which the process
+        requested the kernel write out to permanent storage.
+       </para>
+      </entry>
+     </row>
+
+     <row>
+      <entry role="catalog_table_entry">
+       <para role="column_definition">
+        <structfield>writeback_time</structfield> <type>double precision</type>
+       </para>
+       <para>
+        Time spent in writeback operations in milliseconds (if
+        <xref linkend="guc-track-io-timing"/> is enabled, otherwise zero). This
+        includes the time spent queueing write-out requests and, potentially,
+        the time spent to write out the dirty data.
+       </para>
+      </entry>
+     </row>
+
      <row>
       <entry role="catalog_table_entry">
        <para role="column_definition">
diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 48aacf66ee..d0c932ad0e 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -1131,6 +1131,8 @@ SELECT
        b.read_time,
        b.writes,
        b.write_time,
+       b.writebacks,
+       b.writeback_time,
        b.extends,
        b.extend_time,
        b.op_bytes,
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 041d5dc129..3952476d15 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -1685,7 +1685,7 @@ again:
 		FlushBuffer(buf_hdr, NULL, IOOBJECT_RELATION, io_context);
 		LWLockRelease(content_lock);
 
-		ScheduleBufferTagForWriteback(&BackendWritebackContext,
+		ScheduleBufferTagForWriteback(&BackendWritebackContext, io_context,
 									  &buf_hdr->tag);
 	}
 
@@ -2725,8 +2725,11 @@ BufferSync(int flags)
 		CheckpointWriteDelay(flags, (double) num_processed / num_to_scan);
 	}
 
-	/* issue all pending flushes */
-	IssuePendingWritebacks(&wb_context);
+	/*
+	 * Issue all pending flushes. Only checkpointer calls BufferSync(), so
+	 * IOContext will always be IOCONTEXT_NORMAL.
+	 */
+	IssuePendingWritebacks(&wb_context, IOCONTEXT_NORMAL);
 
 	pfree(per_ts_stat);
 	per_ts_stat = NULL;
@@ -3110,7 +3113,11 @@ SyncOneBuffer(int buf_id, bool skip_recently_used, WritebackContext *wb_context)
 
 	UnpinBuffer(bufHdr);
 
-	ScheduleBufferTagForWriteback(wb_context, &tag);
+	/*
+	 * SyncOneBuffer() is only called by checkpointer and bgwriter, so
+	 * IOContext will always be IOCONTEXT_NORMAL.
+	 */
+	ScheduleBufferTagForWriteback(wb_context, IOCONTEXT_NORMAL, &tag);
 
 	return result | BUF_WRITTEN;
 }
@@ -5445,7 +5452,8 @@ WritebackContextInit(WritebackContext *context, int *max_pending)
  * Add buffer to list of pending writeback requests.
  */
 void
-ScheduleBufferTagForWriteback(WritebackContext *wb_context, BufferTag *tag)
+ScheduleBufferTagForWriteback(WritebackContext *wb_context, IOContext io_context,
+							  BufferTag *tag)
 {
 	PendingWriteback *pending;
 
@@ -5471,7 +5479,7 @@ ScheduleBufferTagForWriteback(WritebackContext *wb_context, BufferTag *tag)
 	 * is now disabled.
 	 */
 	if (wb_context->nr_pending >= *wb_context->max_pending)
-		IssuePendingWritebacks(wb_context);
+		IssuePendingWritebacks(wb_context, io_context);
 }
 
 #define ST_SORT sort_pending_writebacks
@@ -5489,8 +5497,9 @@ ScheduleBufferTagForWriteback(WritebackContext *wb_context, BufferTag *tag)
  * error out - it's just a hint.
  */
 void
-IssuePendingWritebacks(WritebackContext *wb_context)
+IssuePendingWritebacks(WritebackContext *wb_context, IOContext io_context)
 {
+	instr_time	io_start;
 	int			i;
 
 	if (wb_context->nr_pending == 0)
@@ -5502,6 +5511,8 @@ IssuePendingWritebacks(WritebackContext *wb_context)
 	 */
 	sort_pending_writebacks(wb_context->pending_writebacks, wb_context->nr_pending);
 
+	io_start = pgstat_prepare_io_time();
+
 	/*
 	 * Coalesce neighbouring writes, but nothing else. For that we iterate
 	 * through the, now sorted, array of pending flushes, and look forward to
@@ -5555,6 +5566,13 @@ IssuePendingWritebacks(WritebackContext *wb_context)
 		smgrwriteback(reln, BufTagGetForkNum(&tag), tag.blockNum, nblocks);
 	}
 
+	/*
+	 * Assume that writeback requests are only issued for buffers containing
+	 * blocks of permanent relations.
+	 */
+	pgstat_count_io_op_time(IOOBJECT_RELATION, io_context,
+							IOOP_WRITEBACK, io_start, wb_context->nr_pending);
+
 	wb_context->nr_pending = 0;
 }
 
diff --git a/src/backend/utils/activity/pgstat_io.c b/src/backend/utils/activity/pgstat_io.c
index 25735eb6c0..eb7d35d422 100644
--- a/src/backend/utils/activity/pgstat_io.c
+++ b/src/backend/utils/activity/pgstat_io.c
@@ -424,6 +424,14 @@ pgstat_tracks_io_op(BackendType bktype, IOObject io_object,
 		 bktype == B_CHECKPOINTER) && io_op == IOOP_EXTEND)
 		return false;
 
+	/*
+	 * Temporary tables are not logged and thus do not require fsync'ing.
+	 * Writeback is not requested for temporary tables.
+	 */
+	if (io_object == IOOBJECT_TEMP_RELATION &&
+		(io_op == IOOP_FSYNC || io_op == IOOP_WRITEBACK))
+		return false;
+
 	/*
 	 * Some IOOps are not valid in certain IOContexts and some IOOps are only
 	 * valid in certain contexts.
@@ -448,12 +456,6 @@ pgstat_tracks_io_op(BackendType bktype, IOObject io_object,
 	if (strategy_io_context && io_op == IOOP_FSYNC)
 		return false;
 
-	/*
-	 * Temporary tables are not logged and thus do not require fsync'ing.
-	 */
-	if (io_context == IOCONTEXT_NORMAL &&
-		io_object == IOOBJECT_TEMP_RELATION && io_op == IOOP_FSYNC)
-		return false;
 
 	return true;
 }
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 0d57b6a7c0..70da0a2de1 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -1268,6 +1268,8 @@ typedef enum io_stat_col
 	IO_COL_READ_TIME,
 	IO_COL_WRITES,
 	IO_COL_WRITE_TIME,
+	IO_COL_WRITEBACKS,
+	IO_COL_WRITEBACK_TIME,
 	IO_COL_EXTENDS,
 	IO_COL_EXTEND_TIME,
 	IO_COL_CONVERSION,
@@ -1303,6 +1305,8 @@ pgstat_get_io_op_index(IOOp io_op)
 			return IO_COL_REUSES;
 		case IOOP_WRITE:
 			return IO_COL_WRITES;
+		case IOOP_WRITEBACK:
+			return IO_COL_WRITEBACKS;
 	}
 
 	elog(ERROR, "unrecognized IOOp value: %d", io_op);
@@ -1322,6 +1326,7 @@ pgstat_get_io_time_index(IOOp io_op)
 	{
 		case IOOP_READ:
 		case IOOP_WRITE:
+		case IOOP_WRITEBACK:
 		case IOOP_EXTEND:
 		case IOOP_FSYNC:
 			return pgstat_get_io_op_index(io_op) + 1;
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index b2bc81b15f..e766b9b600 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -5760,9 +5760,9 @@
   proname => 'pg_stat_get_io', provolatile => 'v',
   prorows => '30', proretset => 't',
   proparallel => 'r', prorettype => 'record', proargtypes => '',
-  proallargtypes => '{text,text,text,int8,float8,int8,float8,int8,float8,int8,int8,int8,int8,int8,float8,timestamptz}',
-  proargmodes => '{o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}',
-  proargnames => '{backend_type,object,context,reads,read_time,writes,write_time,extends,extend_time,op_bytes,hits,evictions,reuses,fsyncs,fsync_time,stats_reset}',
+  proallargtypes => '{text,text,text,int8,float8,int8,float8,int8,float8,int8,float8,int8,int8,int8,int8,int8,float8,timestamptz}',
+  proargmodes => '{o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o,o}',
+  proargnames => '{backend_type,object,context,reads,read_time,writes,write_time,writebacks,writeback_time,extends,extend_time,op_bytes,hits,evictions,reuses,fsyncs,fsync_time,stats_reset}',
   prosrc => 'pg_stat_get_io' },
 
 { oid => '1136', descr => 'statistics: information about WAL activity',
diff --git a/src/include/pgstat.h b/src/include/pgstat.h
index fff4ad5b6d..57a2c0866a 100644
--- a/src/include/pgstat.h
+++ b/src/include/pgstat.h
@@ -300,9 +300,10 @@ typedef enum IOOp
 	IOOP_READ,
 	IOOP_REUSE,
 	IOOP_WRITE,
+	IOOP_WRITEBACK,
 } IOOp;
 
-#define IOOP_NUM_TYPES (IOOP_WRITE + 1)
+#define IOOP_NUM_TYPES (IOOP_WRITEBACK + 1)
 
 typedef struct PgStat_BktypeIO
 {
diff --git a/src/include/storage/buf_internals.h b/src/include/storage/buf_internals.h
index f8ac811379..30807d5d97 100644
--- a/src/include/storage/buf_internals.h
+++ b/src/include/storage/buf_internals.h
@@ -388,8 +388,9 @@ extern PGDLLIMPORT CkptSortItem *CkptBufferIds;
  */
 /* bufmgr.c */
 extern void WritebackContextInit(WritebackContext *context, int *max_pending);
-extern void IssuePendingWritebacks(WritebackContext *wb_context);
-extern void ScheduleBufferTagForWriteback(WritebackContext *wb_context, BufferTag *tag);
+extern void IssuePendingWritebacks(WritebackContext *wb_context, IOContext io_context);
+extern void ScheduleBufferTagForWriteback(WritebackContext *wb_context,
+										  IOContext io_context, BufferTag *tag);
 
 /* freelist.c */
 extern IOContext IOContextForStrategy(BufferAccessStrategy strategy);
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 69957687fe..0bd6db2bf8 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -1887,6 +1887,8 @@ pg_stat_io| SELECT backend_type,
     read_time,
     writes,
     write_time,
+    writebacks,
+    writeback_time,
     extends,
     extend_time,
     op_bytes,
@@ -1896,7 +1898,7 @@ pg_stat_io| SELECT backend_type,
     fsyncs,
     fsync_time,
     stats_reset
-   FROM pg_stat_get_io() b(backend_type, object, context, reads, read_time, writes, write_time, extends, extend_time, op_bytes, hits, evictions, reuses, fsyncs, fsync_time, stats_reset);
+   FROM pg_stat_get_io() b(backend_type, object, context, reads, read_time, writes, write_time, writebacks, writeback_time, extends, extend_time, op_bytes, hits, evictions, reuses, fsyncs, fsync_time, stats_reset);
 pg_stat_progress_analyze| SELECT s.pid,
     s.datid,
     d.datname,
diff --git a/src/test/regress/expected/stats.out b/src/test/regress/expected/stats.out
index d4e4889e7b..b836d70775 100644
--- a/src/test/regress/expected/stats.out
+++ b/src/test/regress/expected/stats.out
@@ -1386,7 +1386,7 @@ SELECT pg_stat_have_stats('io', 0, 0);
  t
 (1 row)
 
-SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(hits) AS io_stats_pre_reset
+SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(writebacks) + sum(hits) AS io_stats_pre_reset
   FROM pg_stat_io \gset
 SELECT pg_stat_reset_shared('io');
  pg_stat_reset_shared 
@@ -1394,7 +1394,7 @@ SELECT pg_stat_reset_shared('io');
  
 (1 row)
 
-SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(hits) AS io_stats_post_reset
+SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(writebacks) + sum(hits) AS io_stats_post_reset
   FROM pg_stat_io \gset
 SELECT :io_stats_post_reset < :io_stats_pre_reset;
  ?column? 
diff --git a/src/test/regress/sql/stats.sql b/src/test/regress/sql/stats.sql
index 7ba341314f..ec0b98687e 100644
--- a/src/test/regress/sql/stats.sql
+++ b/src/test/regress/sql/stats.sql
@@ -696,10 +696,10 @@ SELECT :io_sum_bulkwrite_strategy_extends_after > :io_sum_bulkwrite_strategy_ext
 
 -- Test IO stats reset
 SELECT pg_stat_have_stats('io', 0, 0);
-SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(hits) AS io_stats_pre_reset
+SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(writebacks) + sum(hits) AS io_stats_pre_reset
   FROM pg_stat_io \gset
 SELECT pg_stat_reset_shared('io');
-SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(hits) AS io_stats_post_reset
+SELECT sum(evictions) + sum(reuses) + sum(extends) + sum(fsyncs) + sum(reads) + sum(writes) + sum(writebacks) + sum(hits) AS io_stats_post_reset
   FROM pg_stat_io \gset
 SELECT :io_stats_post_reset < :io_stats_pre_reset;
 
-- 
2.37.2