v1-0001-Add-pg_buffercache_evict_all-function-for-testing.patch

From 813e5ec0da4c65970b4b1ce2ec2918e4652da9ab Mon Sep 17 00:00:00 2001
From: Nazir Bilal Yavuz <byavuz81@gmail.com>
Date: Fri, 20 Dec 2024 14:06:47 +0300
Subject: [PATCH v1 1/2] Add pg_buffercache_evict_all() function for testing

This new function provides a mechanism to evict all shared buffers at
once. It is designed to address the inefficiency of repeatedly calling
pg_buffercache_evict() for each individual buffer, which can be
time-consuming when dealing with large shared buffer pools
(e.g., ~790ms vs. ~270ms for 16GB of shared buffers).

It is intended for developer testing and debugging purposes and is
available to superusers only.
---
 src/include/storage/bufmgr.h                  |  2 +-
 src/backend/storage/buffer/bufmgr.c           |  5 +-
 doc/src/sgml/pgbuffercache.sgml               | 22 ++++++++-
 contrib/pg_buffercache/Makefile               |  3 +-
 contrib/pg_buffercache/meson.build            |  1 +
 .../pg_buffercache--1.5--1.6.sql              |  7 +++
 contrib/pg_buffercache/pg_buffercache.control |  2 +-
 contrib/pg_buffercache/pg_buffercache_pages.c | 47 ++++++++++++++++++-
 8 files changed, 82 insertions(+), 7 deletions(-)
 create mode 100644 contrib/pg_buffercache/pg_buffercache--1.5--1.6.sql

diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index eb0fba4230b..7f4eeca4afd 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -297,7 +297,7 @@ extern bool BgBufferSync(struct WritebackContext *wb_context);
 extern void LimitAdditionalPins(uint32 *additional_pins);
 extern void LimitAdditionalLocalPins(uint32 *additional_pins);
 
-extern bool EvictUnpinnedBuffer(Buffer buf);
+extern bool EvictUnpinnedBuffer(Buffer buf, bool *flushed);
 
 /* in buf_init.c */
 extern void BufferManagerShmemInit(void);
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 2622221809c..d2a93cf7cc0 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -6098,12 +6098,14 @@ ResOwnerPrintBufferPin(Datum res)
  * or if the buffer becomes dirty again while we're trying to write it out.
  */
 bool
-EvictUnpinnedBuffer(Buffer buf)
+EvictUnpinnedBuffer(Buffer buf, bool *flushed)
 {
 	BufferDesc *desc;
 	uint32		buf_state;
 	bool		result;
 
+	*flushed = false;
+
 	/* Make sure we can pin the buffer. */
 	ResourceOwnerEnlarge(CurrentResourceOwner);
 	ReservePrivateRefCountEntry();
@@ -6134,6 +6136,7 @@ EvictUnpinnedBuffer(Buffer buf)
 		LWLockAcquire(BufferDescriptorGetContentLock(desc), LW_SHARED);
 		FlushBuffer(desc, NULL, IOOBJECT_RELATION, IOCONTEXT_NORMAL);
 		LWLockRelease(BufferDescriptorGetContentLock(desc));
+		*flushed = true;
 	}
 
 	/* This will return false if it becomes dirty or someone else pins it. */
diff --git a/doc/src/sgml/pgbuffercache.sgml b/doc/src/sgml/pgbuffercache.sgml
index 4b90eefc0b0..df4d90a650a 100644
--- a/doc/src/sgml/pgbuffercache.sgml
+++ b/doc/src/sgml/pgbuffercache.sgml
@@ -31,8 +31,9 @@
   This module provides the <function>pg_buffercache_pages()</function>
   function (wrapped in the <structname>pg_buffercache</structname> view),
   the <function>pg_buffercache_summary()</function> function, the
-  <function>pg_buffercache_usage_counts()</function> function and
-  the <function>pg_buffercache_evict()</function> function.
+  <function>pg_buffercache_usage_counts()</function> function, the
+  <function>pg_buffercache_evict()</function> and the
+  <function>pg_buffercache_evict_all()</function> function.
  </para>
 
  <para>
@@ -65,6 +66,12 @@
   function is restricted to superusers only.
  </para>
 
+ <para>
+  The <function>pg_buffercache_evict_all()</function> function tries to evict
+  all buffers in the buffer pool. It returns how many buffers are
+  evicted and flushed. Use of this function is restricted to superusers only.
+ </para>
+
  <sect2 id="pgbuffercache-pg-buffercache">
   <title>The <structname>pg_buffercache</structname> View</title>
 
@@ -378,6 +385,17 @@
   </para>
  </sect2>
 
+ <sect2 id="pgbuffercache-pg-buffercache-evict-all">
+  <title>The <structname>pg_buffercache_evict_all</structname> Function</title>
+  <para>
+   The <function>pg_buffercache_evict_all()</function> function is very similar
+   to <function>pg_buffercache_evict()</function> function.  The difference is,
+   the <function>pg_buffercache_evict_all()</function> does not take argument;
+   instead it tries to evict all buffers in the buffer pool.  The function is
+   intended for developer testing only.
+  </para>
+ </sect2>
+
 <sect2 id="pgbuffercache-sample-output">
   <title>Sample Output</title>
 
diff --git a/contrib/pg_buffercache/Makefile b/contrib/pg_buffercache/Makefile
index eae65ead9e5..2a33602537e 100644
--- a/contrib/pg_buffercache/Makefile
+++ b/contrib/pg_buffercache/Makefile
@@ -8,7 +8,8 @@ OBJS = \
 EXTENSION = pg_buffercache
 DATA = pg_buffercache--1.2.sql pg_buffercache--1.2--1.3.sql \
 	pg_buffercache--1.1--1.2.sql pg_buffercache--1.0--1.1.sql \
-	pg_buffercache--1.3--1.4.sql pg_buffercache--1.4--1.5.sql
+	pg_buffercache--1.3--1.4.sql pg_buffercache--1.4--1.5.sql \
+	pg_buffercache--1.5--1.6.sql
 PGFILEDESC = "pg_buffercache - monitoring of shared buffer cache in real-time"
 
 REGRESS = pg_buffercache
diff --git a/contrib/pg_buffercache/meson.build b/contrib/pg_buffercache/meson.build
index 1ca3452918b..1ff57aa22e9 100644
--- a/contrib/pg_buffercache/meson.build
+++ b/contrib/pg_buffercache/meson.build
@@ -23,6 +23,7 @@ install_data(
   'pg_buffercache--1.2.sql',
   'pg_buffercache--1.3--1.4.sql',
   'pg_buffercache--1.4--1.5.sql',
+  'pg_buffercache--1.5--1.6.sql',
   'pg_buffercache.control',
   kwargs: contrib_data_args,
 )
diff --git a/contrib/pg_buffercache/pg_buffercache--1.5--1.6.sql b/contrib/pg_buffercache/pg_buffercache--1.5--1.6.sql
new file mode 100644
index 00000000000..c08b799be94
--- /dev/null
+++ b/contrib/pg_buffercache/pg_buffercache--1.5--1.6.sql
@@ -0,0 +1,7 @@
+\echo Use "ALTER EXTENSION pg_buffercache UPDATE TO '1.6'" to load this file. \quit
+
+CREATE FUNCTION pg_buffercache_evict_all(
+    OUT buffers_evicted int4,
+    OUT buffers_flushed int4)
+AS 'MODULE_PATHNAME', 'pg_buffercache_evict_all'
+LANGUAGE C PARALLEL SAFE VOLATILE;
diff --git a/contrib/pg_buffercache/pg_buffercache.control b/contrib/pg_buffercache/pg_buffercache.control
index 5ee875f77dd..b030ba3a6fa 100644
--- a/contrib/pg_buffercache/pg_buffercache.control
+++ b/contrib/pg_buffercache/pg_buffercache.control
@@ -1,5 +1,5 @@
 # pg_buffercache extension
 comment = 'examine the shared buffer cache'
-default_version = '1.5'
+default_version = '1.6'
 module_pathname = '$libdir/pg_buffercache'
 relocatable = true
diff --git a/contrib/pg_buffercache/pg_buffercache_pages.c b/contrib/pg_buffercache/pg_buffercache_pages.c
index 3ae0a018e10..ea7c0e6934c 100644
--- a/contrib/pg_buffercache/pg_buffercache_pages.c
+++ b/contrib/pg_buffercache/pg_buffercache_pages.c
@@ -19,6 +19,7 @@
 #define NUM_BUFFERCACHE_PAGES_ELEM	9
 #define NUM_BUFFERCACHE_SUMMARY_ELEM 5
 #define NUM_BUFFERCACHE_USAGE_COUNTS_ELEM 4
+#define NUM_BUFFERCACHE_EVICT_ALL_ELEM 2
 
 PG_MODULE_MAGIC;
 
@@ -64,6 +65,7 @@ PG_FUNCTION_INFO_V1(pg_buffercache_pages);
 PG_FUNCTION_INFO_V1(pg_buffercache_summary);
 PG_FUNCTION_INFO_V1(pg_buffercache_usage_counts);
 PG_FUNCTION_INFO_V1(pg_buffercache_evict);
+PG_FUNCTION_INFO_V1(pg_buffercache_evict_all);
 
 Datum
 pg_buffercache_pages(PG_FUNCTION_ARGS)
@@ -356,6 +358,7 @@ Datum
 pg_buffercache_evict(PG_FUNCTION_ARGS)
 {
 	Buffer		buf = PG_GETARG_INT32(0);
+	bool		flushed;
 
 	if (!superuser())
 		ereport(ERROR,
@@ -365,5 +368,47 @@ pg_buffercache_evict(PG_FUNCTION_ARGS)
 	if (buf < 1 || buf > NBuffers)
 		elog(ERROR, "bad buffer ID: %d", buf);
 
-	PG_RETURN_BOOL(EvictUnpinnedBuffer(buf));
+	PG_RETURN_BOOL(EvictUnpinnedBuffer(buf, &flushed));
+}
+
+/*
+ * Try to evict all shared buffers.
+ */
+Datum
+pg_buffercache_evict_all(PG_FUNCTION_ARGS)
+{
+	Datum		result;
+	TupleDesc	tupledesc;
+	HeapTuple	tuple;
+	Datum		values[NUM_BUFFERCACHE_EVICT_ALL_ELEM];
+	bool		nulls[NUM_BUFFERCACHE_EVICT_ALL_ELEM] = {0};
+
+	int32		buffers_evicted = 0;
+	int32		buffers_flushed = 0;
+	bool		flushed;
+
+	if (get_call_result_type(fcinfo, NULL, &tupledesc) != TYPEFUNC_COMPOSITE)
+		elog(ERROR, "return type must be a row type");
+
+	if (!superuser())
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+				 errmsg("must be superuser to use pg_buffercache_evict_all function")));
+
+	for (int buf = 1; buf < NBuffers; buf++)
+	{
+		if (EvictUnpinnedBuffer(buf, &flushed))
+			buffers_evicted++;
+		if (flushed)
+			buffers_flushed++;
+	}
+
+	values[0] = Int32GetDatum(buffers_evicted);
+	values[1] = Int32GetDatum(buffers_flushed);
+
+	/* Build and return the tuple. */
+	tuple = heap_form_tuple(tupledesc, values, nulls);
+	result = HeapTupleGetDatum(tuple);
+
+	PG_RETURN_DATUM(result);
 }
-- 
2.45.2