v13-0001-Make-all-SLRU-buffer-sizes-configurable.patch

From 5f5d4ed8ae2808766ac1fd48f68602ef530e3833 Mon Sep 17 00:00:00 2001
From: Andrey Borodin <amborodin@acm.org>
Date: Mon, 15 Feb 2021 21:51:56 +0500
Subject: [PATCH v13 1/5] Make all SLRU buffer sizes configurable.

Provide new GUCs to set the number of buffers, instead of using hard
coded defaults.

Author: Andrey M. Borodin <x4mmm@yandex-team.ru>
Reviewed-by: Anastasia Lubennikova <a.lubennikova@postgrespro.ru>
Reviewed-by: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Reviewed-by: Alexander Korotkov <aekorotkov@gmail.com>
Reviewed-by: Gilles Darold <gilles@darold.net>
Reviewed-by: Thomas Munro <thomas.munro@gmail.com>
Discussion: https://postgr.es/m/2BEC2B3F-9B61-4C1D-9FB5-5FAB0F05EF86%40yandex-team.ru
---
 doc/src/sgml/config.sgml                      | 137 ++++++++++++++++++
 src/backend/access/transam/clog.c             |   6 +
 src/backend/access/transam/commit_ts.c        |   5 +-
 src/backend/access/transam/multixact.c        |   8 +-
 src/backend/access/transam/subtrans.c         |   5 +-
 src/backend/commands/async.c                  |   8 +-
 src/backend/storage/lmgr/predicate.c          |   4 +-
 src/backend/utils/init/globals.c              |   8 +
 src/backend/utils/misc/guc.c                  |  77 ++++++++++
 src/backend/utils/misc/postgresql.conf.sample |   9 ++
 src/include/access/multixact.h                |   4 -
 src/include/access/subtrans.h                 |   3 -
 src/include/commands/async.h                  |   5 -
 src/include/miscadmin.h                       |   7 +
 src/include/storage/predicate.h               |   4 -
 15 files changed, 261 insertions(+), 29 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index ddc6d789d8..f1112bfa9c 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1886,6 +1886,143 @@ include_dir 'conf.d'
        </para>
       </listitem>
      </varlistentry>
+     
+    <varlistentry id="guc-multixact-offsets-buffers" xreflabel="multixact_offsets_buffers">
+      <term><varname>multixact_offsets_buffers</varname> (<type>integer</type>)
+      <indexterm>
+       <primary><varname>multixact_offsets_buffers</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Specifies the amount of shared memory to used to cache the contents
+        of <literal>pg_multixact/offsets</literal> (see
+        <xref linkend="pgdata-contents-table"/>).
+        If this value is specified without units, it is taken as blocks,
+        that is <symbol>BLCKSZ</symbol> bytes, typically 8kB.
+        The default value is <literal>8</literal>.
+        This parameter can only be set at server start.
+       </para>
+      </listitem>
+     </varlistentry>
+
+    <varlistentry id="guc-multixact-members-buffers" xreflabel="multixact_members_buffers">
+      <term><varname>multixact_members_buffers</varname> (<type>integer</type>)
+      <indexterm>
+       <primary><varname>multixact_members_buffers</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Specifies the amount of shared memory to used to cache the contents
+        of <literal>pg_multixact/members</literal> (see
+        <xref linkend="pgdata-contents-table"/>).
+        If this value is specified without units, it is taken as blocks,
+        that is <symbol>BLCKSZ</symbol> bytes, typically 8kB.
+        The default value is <literal>16</literal>.
+        This parameter can only be set at server start.
+       </para>
+      </listitem>
+     </varlistentry>
+     
+    <varlistentry id="guc-subtrans-buffers" xreflabel="subtrans_buffers">
+      <term><varname>subtrans_buffers</varname> (<type>integer</type>)
+      <indexterm>
+       <primary><varname>subtrans_buffers</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Specifies the amount of shared memory to used to cache the contents
+        of <literal>pg_subtrans</literal> (see
+        <xref linkend="pgdata-contents-table"/>).
+        If this value is specified without units, it is taken as blocks,
+        that is <symbol>BLCKSZ</symbol> bytes, typically 8kB.
+        The default value is <literal>8</literal>.
+        This parameter can only be set at server start.
+       </para>
+      </listitem>
+     </varlistentry>
+     
+    <varlistentry id="guc-notify-buffers" xreflabel="notify_buffers">
+      <term><varname>notify_buffers</varname> (<type>integer</type>)
+      <indexterm>
+       <primary><varname>notify_buffers</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Specifies the amount of shared memory to used to cache the contents
+        of <literal>pg_notify</literal> (see
+        <xref linkend="pgdata-contents-table"/>).
+        If this value is specified without units, it is taken as blocks,
+        that is <symbol>BLCKSZ</symbol> bytes, typically 8kB.
+        The default value is <literal>8</literal>.
+        This parameter can only be set at server start.
+       </para>
+      </listitem>
+     </varlistentry>
+     
+    <varlistentry id="guc-serial-buffers" xreflabel="serial_buffers">
+      <term><varname>serial_buffers</varname> (<type>integer</type>)
+      <indexterm>
+       <primary><varname>serial_buffers</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Specifies the amount of shared memory to used to cache the contents
+        of <literal>pg_serial</literal> (see
+        <xref linkend="pgdata-contents-table"/>).
+        If this value is specified without units, it is taken as blocks,
+        that is <symbol>BLCKSZ</symbol> bytes, typically 8kB.
+        The default value is <literal>16</literal>.
+        This parameter can only be set at server start.
+       </para>
+      </listitem>
+     </varlistentry>
+     
+    <varlistentry id="guc-clog-buffers" xreflabel="clog_buffers">
+      <term><varname>clog_buffers</varname> (<type>integer</type>)
+      <indexterm>
+       <primary><varname>clog_buffers</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Specifies the amount of shared memory to used to cache the contents
+        of <literal>pg_xact</literal> (see
+        <xref linkend="pgdata-contents-table"/>).
+        If this value is specified without units, it is taken as blocks,
+        that is <symbol>BLCKSZ</symbol> bytes, typically 8kB.
+        The default value is <literal>0</literal>, which requests
+        <varname>shared_buffers</varname> / 512, but not more than 128 or
+        fewer than 4 blocks.
+        This parameter can only be set at server start.
+       </para>
+      </listitem>
+     </varlistentry>
+     
+    <varlistentry id="guc-commit-ts-buffers" xreflabel="commit_ts_buffers">
+      <term><varname>commit_ts_buffers</varname> (<type>integer</type>)
+      <indexterm>
+       <primary><varname>commit_ts_buffers</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Specifies the amount of memory to be used to cache the cotents of
+        <literal>pg_commit_ts</literal> (see
+        <xref linkend="pgdata-contents-table"/>).
+        If this value is specified without units, it is taken as blocks,
+        that is <symbol>BLCKSZ</symbol> bytes, typically 8kB.
+        The default value is <literal>0</literal>, which requests
+        <varname>shared_buffers</varname> / 512, but not more than 128 or
+        fewer than 16 blocks.
+        This parameter can only be set at server start.
+       </para>
+      </listitem>
+     </varlistentry>
 
      <varlistentry id="guc-max-stack-depth" xreflabel="max_stack_depth">
       <term><varname>max_stack_depth</varname> (<type>integer</type>)
diff --git a/src/backend/access/transam/clog.c b/src/backend/access/transam/clog.c
index 6fa4713fb4..0318e8ff59 100644
--- a/src/backend/access/transam/clog.c
+++ b/src/backend/access/transam/clog.c
@@ -659,6 +659,9 @@ TransactionIdGetStatus(TransactionId xid, XLogRecPtr *lsn)
 /*
  * Number of shared CLOG buffers.
  *
+ * If values is configured via GUC - just use given value. Otherwise
+ * apply following euristics.
+ *
  * On larger multi-processor systems, it is possible to have many CLOG page
  * requests in flight at one time which could lead to disk access for CLOG
  * page if the required page is not found in memory.  Testing revealed that we
@@ -675,6 +678,9 @@ TransactionIdGetStatus(TransactionId xid, XLogRecPtr *lsn)
 Size
 CLOGShmemBuffers(void)
 {
+	/* consider 0 and 1 as unset GUC */
+	if (clog_buffers > 1)
+		return clog_buffers;
 	return Min(128, Max(4, NBuffers / 512));
 }
 
diff --git a/src/backend/access/transam/commit_ts.c b/src/backend/access/transam/commit_ts.c
index 268bdba339..0d2632b90e 100644
--- a/src/backend/access/transam/commit_ts.c
+++ b/src/backend/access/transam/commit_ts.c
@@ -530,7 +530,10 @@ pg_xact_commit_timestamp_origin(PG_FUNCTION_ARGS)
 Size
 CommitTsShmemBuffers(void)
 {
-	return Min(16, Max(4, NBuffers / 1024));
+	/* consider 0 and 1 as unset GUC */
+	if (commit_ts_buffers > 1)
+		return commit_ts_buffers;
+	return Min(16, Max(4, NBuffers / 512));
 }
 
 /*
diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
index 1f9f1a1fa1..21787765e2 100644
--- a/src/backend/access/transam/multixact.c
+++ b/src/backend/access/transam/multixact.c
@@ -1831,8 +1831,8 @@ MultiXactShmemSize(void)
 			 mul_size(sizeof(MultiXactId) * 2, MaxOldestSlot))
 
 	size = SHARED_MULTIXACT_STATE_SIZE;
-	size = add_size(size, SimpleLruShmemSize(NUM_MULTIXACTOFFSET_BUFFERS, 0));
-	size = add_size(size, SimpleLruShmemSize(NUM_MULTIXACTMEMBER_BUFFERS, 0));
+	size = add_size(size, SimpleLruShmemSize(multixact_offsets_buffers, 0));
+	size = add_size(size, SimpleLruShmemSize(multixact_members_buffers, 0));
 
 	return size;
 }
@@ -1848,13 +1848,13 @@ MultiXactShmemInit(void)
 	MultiXactMemberCtl->PagePrecedes = MultiXactMemberPagePrecedes;
 
 	SimpleLruInit(MultiXactOffsetCtl,
-				  "MultiXactOffset", NUM_MULTIXACTOFFSET_BUFFERS, 0,
+				  "MultiXactOffset", multixact_offsets_buffers, 0,
 				  MultiXactOffsetSLRULock, "pg_multixact/offsets",
 				  LWTRANCHE_MULTIXACTOFFSET_BUFFER,
 				  SYNC_HANDLER_MULTIXACT_OFFSET);
 	SlruPagePrecedesUnitTests(MultiXactOffsetCtl, MULTIXACT_OFFSETS_PER_PAGE);
 	SimpleLruInit(MultiXactMemberCtl,
-				  "MultiXactMember", NUM_MULTIXACTMEMBER_BUFFERS, 0,
+				  "MultiXactMember", multixact_offsets_buffers, 0,
 				  MultiXactMemberSLRULock, "pg_multixact/members",
 				  LWTRANCHE_MULTIXACTMEMBER_BUFFER,
 				  SYNC_HANDLER_MULTIXACT_MEMBER);
diff --git a/src/backend/access/transam/subtrans.c b/src/backend/access/transam/subtrans.c
index 6a8e521f89..785f2520fd 100644
--- a/src/backend/access/transam/subtrans.c
+++ b/src/backend/access/transam/subtrans.c
@@ -31,6 +31,7 @@
 #include "access/slru.h"
 #include "access/subtrans.h"
 #include "access/transam.h"
+#include "miscadmin.h"
 #include "pg_trace.h"
 #include "utils/snapmgr.h"
 
@@ -184,14 +185,14 @@ SubTransGetTopmostTransaction(TransactionId xid)
 Size
 SUBTRANSShmemSize(void)
 {
-	return SimpleLruShmemSize(NUM_SUBTRANS_BUFFERS, 0);
+	return SimpleLruShmemSize(subtrans_buffers, 0);
 }
 
 void
 SUBTRANSShmemInit(void)
 {
 	SubTransCtl->PagePrecedes = SubTransPagePrecedes;
-	SimpleLruInit(SubTransCtl, "Subtrans", NUM_SUBTRANS_BUFFERS, 0,
+	SimpleLruInit(SubTransCtl, "Subtrans", subtrans_buffers, 0,
 				  SubtransSLRULock, "pg_subtrans",
 				  LWTRANCHE_SUBTRANS_BUFFER, SYNC_HANDLER_NONE);
 	SlruPagePrecedesUnitTests(SubTransCtl, SUBTRANS_XACTS_PER_PAGE);
diff --git a/src/backend/commands/async.c b/src/backend/commands/async.c
index 4b16fb5682..de17f52cd7 100644
--- a/src/backend/commands/async.c
+++ b/src/backend/commands/async.c
@@ -107,7 +107,7 @@
  * frontend during startup.)  The above design guarantees that notifies from
  * other backends will never be missed by ignoring self-notifies.
  *
- * The amount of shared memory used for notify management (NUM_NOTIFY_BUFFERS)
+ * The amount of shared memory used for notify management (notify_buffers)
  * can be varied without affecting anything but performance.  The maximum
  * amount of notification data that can be queued at one time is determined
  * by slru.c's wraparound limit; see QUEUE_MAX_PAGE below.
@@ -225,7 +225,7 @@ typedef struct QueuePosition
  *
  * Resist the temptation to make this really large.  While that would save
  * work in some places, it would add cost in others.  In particular, this
- * should likely be less than NUM_NOTIFY_BUFFERS, to ensure that backends
+ * should likely be less than notify_buffers, to ensure that backends
  * catch up before the pages they'll need to read fall out of SLRU cache.
  */
 #define QUEUE_CLEANUP_DELAY 4
@@ -514,7 +514,7 @@ AsyncShmemSize(void)
 	size = mul_size(MaxBackends + 1, sizeof(QueueBackendStatus));
 	size = add_size(size, offsetof(AsyncQueueControl, backend));
 
-	size = add_size(size, SimpleLruShmemSize(NUM_NOTIFY_BUFFERS, 0));
+	size = add_size(size, SimpleLruShmemSize(notify_buffers, 0));
 
 	return size;
 }
@@ -562,7 +562,7 @@ AsyncShmemInit(void)
 	 * Set up SLRU management of the pg_notify data.
 	 */
 	NotifyCtl->PagePrecedes = asyncQueuePagePrecedes;
-	SimpleLruInit(NotifyCtl, "Notify", NUM_NOTIFY_BUFFERS, 0,
+	SimpleLruInit(NotifyCtl, "Notify", notify_buffers, 0,
 				  NotifySLRULock, "pg_notify", LWTRANCHE_NOTIFY_BUFFER,
 				  SYNC_HANDLER_NONE);
 
diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c
index d493aeef0f..b1f4f1651d 100644
--- a/src/backend/storage/lmgr/predicate.c
+++ b/src/backend/storage/lmgr/predicate.c
@@ -872,7 +872,7 @@ SerialInit(void)
 	 */
 	SerialSlruCtl->PagePrecedes = SerialPagePrecedesLogically;
 	SimpleLruInit(SerialSlruCtl, "Serial",
-				  NUM_SERIAL_BUFFERS, 0, SerialSLRULock, "pg_serial",
+				  serial_buffers, 0, SerialSLRULock, "pg_serial",
 				  LWTRANCHE_SERIAL_BUFFER, SYNC_HANDLER_NONE);
 #ifdef USE_ASSERT_CHECKING
 	SerialPagePrecedesLogicallyUnitTests();
@@ -1395,7 +1395,7 @@ PredicateLockShmemSize(void)
 
 	/* Shared memory structures for SLRU tracking of old committed xids. */
 	size = add_size(size, sizeof(SerialControlData));
-	size = add_size(size, SimpleLruShmemSize(NUM_SERIAL_BUFFERS, 0));
+	size = add_size(size, SimpleLruShmemSize(serial_buffers, 0));
 
 	return size;
 }
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index 73e0a672ae..e90275be6c 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -148,3 +148,11 @@ int64		VacuumPageDirty = 0;
 
 int			VacuumCostBalance = 0;	/* working state for vacuum */
 bool		VacuumCostActive = false;
+
+int			multixact_offsets_buffers = 8;
+int			multixact_members_buffers = 16;
+int			subtrans_buffers = 32;
+int			notify_buffers = 8;
+int			serial_buffers = 16;
+int			clog_buffers = 0;
+int			commit_ts_buffers = 0;
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 0c5dc4d3e8..003bc820d2 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2305,6 +2305,83 @@ static struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"multixact_offsets_buffers", PGC_POSTMASTER, RESOURCES_MEM,
+			gettext_noop("Sets the number of shared memory buffers used for MultiXact offsets SLRU."),
+			NULL,
+			GUC_UNIT_BLOCKS
+		},
+		&multixact_offsets_buffers,
+		8, 2, INT_MAX / 2,
+		NULL, NULL, NULL
+	},
+
+	{
+		{"multixact_members_buffers", PGC_POSTMASTER, RESOURCES_MEM,
+			gettext_noop("Sets the number of shared memory buffers used for MultiXact members SLRU."),
+			NULL,
+			GUC_UNIT_BLOCKS
+		},
+		&multixact_members_buffers,
+		16, 2, INT_MAX / 2,
+		NULL, NULL, NULL
+	},
+
+	{
+		{"subtrans_buffers", PGC_POSTMASTER, RESOURCES_MEM,
+			gettext_noop("Sets the number of shared memory buffers used for substransactions SLRU."),
+			NULL,
+			GUC_UNIT_BLOCKS
+		},
+		&subtrans_buffers,
+		32, 2, INT_MAX / 2,
+		NULL, NULL, NULL
+	},
+
+	{
+		{"notify_buffers", PGC_POSTMASTER, RESOURCES_MEM,
+			gettext_noop("Sets the number of shared memory buffers used for asyncronous notifications SLRU."),
+			NULL,
+			GUC_UNIT_BLOCKS
+		},
+		&notify_buffers,
+		8, 2, INT_MAX / 2,
+		NULL, NULL, NULL
+	},
+
+	{
+		{"serial_buffers", PGC_POSTMASTER, RESOURCES_MEM,
+			gettext_noop("Sets the number of shared memory buffers used for predicate locks SLRU."),
+			NULL,
+			GUC_UNIT_BLOCKS
+		},
+		&serial_buffers,
+		16, 2, INT_MAX / 2,
+		NULL, NULL, NULL
+	},
+
+	{
+		{"clog_buffers", PGC_POSTMASTER, RESOURCES_MEM,
+			gettext_noop("Sets the number of shared memory buffers used for commit log SLRU."),
+			NULL,
+			GUC_UNIT_BLOCKS
+		},
+		&clog_buffers,
+		0, 0, INT_MAX / 2,
+		NULL, NULL, NULL
+	},
+
+	{
+		{"commit_ts_buffers", PGC_POSTMASTER, RESOURCES_MEM,
+			gettext_noop("Sets the number of shared memory buffers used for commit timestamps SLRU."),
+			NULL,
+			GUC_UNIT_BLOCKS
+		},
+		&commit_ts_buffers,
+		0, 0, INT_MAX / 2,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"temp_buffers", PGC_USERSET, RESOURCES_MEM,
 			gettext_noop("Sets the maximum number of temporary buffers used by each session."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index b234a6bfe6..1b8515989b 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -190,6 +190,15 @@
 					# (change requires restart)
 #backend_flush_after = 0		# measured in pages, 0 disables
 
+# - SLRU Buffers (change requires restart) -
+
+#clog_buffers = 0			# memory for pg_xact (0 = auto)
+#subtrans_buffers = 32			# memory for pg_subtrans
+#multixact_offsets_buffers = 8		# memory for pg_multixact/offsets
+#multixact_members_buffers = 16		# memory for pg_multixact/members
+#notify_buffers = 8			# memory for pg_nofity
+#serial_buffers = 16			# memory for pg_serial
+#commit_ts_buffers = 0			# memory for pg_commit_ts (0 = auto)
 
 #------------------------------------------------------------------------------
 # WRITE-AHEAD LOG
diff --git a/src/include/access/multixact.h b/src/include/access/multixact.h
index 4bbb035eae..97c0a46376 100644
--- a/src/include/access/multixact.h
+++ b/src/include/access/multixact.h
@@ -29,10 +29,6 @@
 
 #define MaxMultiXactOffset	((MultiXactOffset) 0xFFFFFFFF)
 
-/* Number of SLRU buffers to use for multixact */
-#define NUM_MULTIXACTOFFSET_BUFFERS		8
-#define NUM_MULTIXACTMEMBER_BUFFERS		16
-
 /*
  * Possible multixact lock modes ("status").  The first four modes are for
  * tuple locks (FOR KEY SHARE, FOR SHARE, FOR NO KEY UPDATE, FOR UPDATE); the
diff --git a/src/include/access/subtrans.h b/src/include/access/subtrans.h
index d0ab44ae82..ca0999056e 100644
--- a/src/include/access/subtrans.h
+++ b/src/include/access/subtrans.h
@@ -11,9 +11,6 @@
 #ifndef SUBTRANS_H
 #define SUBTRANS_H
 
-/* Number of SLRU buffers to use for subtrans */
-#define NUM_SUBTRANS_BUFFERS	32
-
 extern void SubTransSetParent(TransactionId xid, TransactionId parent);
 extern TransactionId SubTransGetParent(TransactionId xid);
 extern TransactionId SubTransGetTopmostTransaction(TransactionId xid);
diff --git a/src/include/commands/async.h b/src/include/commands/async.h
index 9217f66b91..fa831e3721 100644
--- a/src/include/commands/async.h
+++ b/src/include/commands/async.h
@@ -15,11 +15,6 @@
 
 #include <signal.h>
 
-/*
- * The number of SLRU page buffers we use for the notification queue.
- */
-#define NUM_NOTIFY_BUFFERS	8
-
 extern bool Trace_notify;
 extern volatile sig_atomic_t notifyInterruptPending;
 
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index 013850ac28..9c325b4312 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -162,6 +162,13 @@ extern PGDLLIMPORT int MaxBackends;
 extern PGDLLIMPORT int MaxConnections;
 extern PGDLLIMPORT int max_worker_processes;
 extern PGDLLIMPORT int max_parallel_workers;
+extern PGDLLIMPORT int multixact_offsets_buffers;
+extern PGDLLIMPORT int multixact_members_buffers;
+extern PGDLLIMPORT int subtrans_buffers;
+extern PGDLLIMPORT int notify_buffers;
+extern PGDLLIMPORT int serial_buffers;
+extern PGDLLIMPORT int clog_buffers;
+extern PGDLLIMPORT int commit_ts_buffers;
 
 extern PGDLLIMPORT int MyProcPid;
 extern PGDLLIMPORT pg_time_t MyStartTime;
diff --git a/src/include/storage/predicate.h b/src/include/storage/predicate.h
index 152b698611..c72779bd88 100644
--- a/src/include/storage/predicate.h
+++ b/src/include/storage/predicate.h
@@ -26,10 +26,6 @@ extern int	max_predicate_locks_per_xact;
 extern int	max_predicate_locks_per_relation;
 extern int	max_predicate_locks_per_page;
 
-
-/* Number of SLRU buffers to use for Serial SLRU */
-#define NUM_SERIAL_BUFFERS		16
-
 /*
  * A handle used for sharing SERIALIZABLEXACT objects between the participants
  * in a parallel query.
-- 
2.30.1