From 520686d6cc22a599bc06b91391171ca218c3db75 Mon Sep 17 00:00:00 2001
From: Andrey Borodin <amborodin@acm.org>
Date: Mon, 11 May 2020 16:17:02 +0500
Subject: [PATCH v2 2/4] 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       |  1 +
 src/backend/utils/misc/guc.c           | 10 ++++++++++
 src/include/miscadmin.h                |  1 +
 5 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 94d99373a7..31d7c1f4b3 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1777,6 +1777,22 @@ 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 241d9dd78d..445b6258a4 100644
--- a/src/backend/access/transam/multixact.c
+++ b/src/backend/access/transam/multixact.c
@@ -1589,7 +1589,7 @@ 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 01e739da40..f404167ad0 100644
--- a/src/backend/utils/init/globals.c
+++ b/src/backend/utils/init/globals.c
@@ -151,3 +151,4 @@ double		vacuum_cleanup_index_scale_factor;
 
 int			multixact_offsets_slru_buffers = 8;
 int			multixact_members_slru_buffers = 16;
+int			multixact_local_cache_entries = 256;
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index d1fbb75cd5..6443f595cc 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2273,6 +2273,16 @@ static struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"multixact_local_cache_entries", PGC_SUSET, RESOURCES_MEM,
+			gettext_noop("Sets the number 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 bb1475ad2b..9ce2adea63 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -163,6 +163,7 @@ extern PGDLLIMPORT int max_worker_processes;
 extern PGDLLIMPORT int max_parallel_workers;
 extern PGDLLIMPORT int multixact_offsets_slru_buffers;
 extern PGDLLIMPORT int multixact_members_slru_buffers;
+extern PGDLLIMPORT int multixact_local_cache_entries;
 
 extern PGDLLIMPORT int MyProcPid;
 extern PGDLLIMPORT pg_time_t MyStartTime;
-- 
2.24.2 (Apple Git-127)