From 68ea2b7f9b52d35b5fcd9c8d44d88de5a64be3ba Mon Sep 17 00:00:00 2001
From: Simon Riggs <simon@2ndQuadrant.com>
Date: Wed, 5 Apr 2017 18:22:32 -0400
Subject: [PATCH] Reduce lock level for CREATE STATISTICS

In line with other lock reductions related to planning.

Simon Riggs
---
 doc/src/sgml/mvcc.sgml           | 3 ++-
 src/backend/commands/statscmds.c | 8 +++++++-
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
index 82e69fe2d2..7aa32932fa 100644
--- a/doc/src/sgml/mvcc.sgml
+++ b/doc/src/sgml/mvcc.sgml
@@ -923,7 +923,8 @@ ERROR:  could not serialize access due to read/write dependencies among transact
 
         <para>
          Acquired by <command>VACUUM</command> (without <option>FULL</option>),
-         <command>ANALYZE</>, <command>CREATE INDEX CONCURRENTLY</>, and
+         <command>ANALYZE</>, <command>CREATE INDEX CONCURRENTLY</>,
+         <command>CREATE STATISTICS</> and
          <command>ALTER TABLE VALIDATE</command> and other
          <command>ALTER TABLE</command> variants (for full details see
          <xref linkend="SQL-ALTERTABLE">).
diff --git a/src/backend/commands/statscmds.c b/src/backend/commands/statscmds.c
index 8d483dbb3a..46abadcc81 100644
--- a/src/backend/commands/statscmds.c
+++ b/src/backend/commands/statscmds.c
@@ -96,7 +96,13 @@ CreateStatistics(CreateStatsStmt *stmt)
 				 errmsg("statistics \"%s\" already exist", namestr)));
 	}
 
-	rel = heap_openrv(stmt->relation, AccessExclusiveLock);
+	/*
+	 * CREATE STATISTICS will influence future execution plans but does
+	 * not interfere with currently executing plans so it is safe to
+	 * take only ShareUpdateExclusiveLock on relation, conflicting with
+	 * ANALYZE and other DDL that sets statistical information.
+	 */
+	rel = heap_openrv(stmt->relation, ShareUpdateExclusiveLock);
 	relid = RelationGetRelid(rel);
 
 	if (rel->rd_rel->relkind != RELKIND_RELATION &&