From b1af887f4c4e5402dce1b6ea226ac8b81b92443f Mon Sep 17 00:00:00 2001
From: Alexander Korotkov <akorotkov@postgresql.org>
Date: Mon, 26 Oct 2020 03:44:50 +0300
Subject: [PATCH 2/3] Make MultiXact local cache size configurable

---
 doc/src/sgml/config.sgml               | 16 ++++++++++++++++
 src/backend/access/transam/multixact.c |  2 +-
 src/backend/utils/init/globals.c       |  2 ++
 src/backend/utils/misc/guc.c           | 10 ++++++++++
 src/include/miscadmin.h                |  2 ++
 5 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index f043433e318..fd4ca293476 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1823,6 +1823,22 @@ include_dir 'conf.d'
       </listitem>
      </varlistentry>
 
+    <varlistentry id="guc-multixact-local-cache-entries" xreflabel="multixact_local-cache-entries">
+      <term><varname>multixact_local_cache_entries</varname> (<type>integer</type>)
+      <indexterm>
+       <primary><varname>multixact_local_cache_entries</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Specifies the number cached MultiXact by backend. Any SLRU lookup is preceeded
+        by cache lookup. Higher numbers of cache size help to deduplicate lock sets, while
+        lower values make cache lookup faster.
+        It defaults to 256.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-max-stack-depth" xreflabel="max_stack_depth">
       <term><varname>max_stack_depth</varname> (<type>integer</type>)
       <indexterm>
diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c
index ccbce90f0ea..57be24c0cc1 100644
--- a/src/backend/access/transam/multixact.c
+++ b/src/backend/access/transam/multixact.c
@@ -1613,7 +1613,7 @@ mXactCachePut(MultiXactId multi, int nmembers, MultiXactMember *members)
 	qsort(entry->members, nmembers, sizeof(MultiXactMember), mxactMemberComparator);
 
 	dlist_push_head(&MXactCache, &entry->node);
-	if (MXactCacheMembers++ >= MAX_CACHE_ENTRIES)
+	if (MXactCacheMembers++ >= multixact_local_cache_entries)
 	{
 		dlist_node *node;
 		mXactCacheEnt *entry;
diff --git a/src/backend/utils/init/globals.c b/src/backend/utils/init/globals.c
index 6ab82168398..9ca71933dcc 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -149,3 +149,5 @@ int			VacuumCostBalance = 0;	/* working state for vacuum */
 bool		VacuumCostActive = false;
 
 double		vacuum_cleanup_index_scale_factor;
+
+int         multixact_local_cache_entries = 256;
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index a62d64eaa47..d667578cc33 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2257,6 +2257,16 @@ static struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"multixact_local_cache_entries", PGC_SUSET, RESOURCES_MEM,
+			gettext_noop("Sets the number of cached MultiXact by backend."),
+			NULL
+		},
+		&multixact_local_cache_entries,
+		256, 2, 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/include/miscadmin.h b/src/include/miscadmin.h
index 72e33523984..01af61c963a 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -162,6 +162,8 @@ extern PGDLLIMPORT int MaxConnections;
 extern PGDLLIMPORT int max_worker_processes;
 extern PGDLLIMPORT int max_parallel_workers;
 
+extern PGDLLIMPORT int multixact_local_cache_entries;
+
 extern PGDLLIMPORT int MyProcPid;
 extern PGDLLIMPORT pg_time_t MyStartTime;
 extern PGDLLIMPORT TimestampTz MyStartTimestamp;
-- 
2.14.3