Reduce lock level for CREATE STATISTICS

In line with other lock reductions related to planning.

Simon Riggs

diff --git a/doc/src/sgml/mvcc.sgml b/doc/src/sgml/mvcc.sgml
index 82e69fe2d277e9fb58e3347b02bf4f33a342b0ca..7aa32932fab129639f81578d9decfd9907a18ab4 100644 (file)
--- 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 8d483dbb3a7cc3ce17631a687d0080a50261a9cc..46abadcc811f753242d0eb870c0a130dd5ff40be 100644 (file)
--- 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 &&