Fix snapshot leak warning for some procedures

The problem arises with the combination of CALL with output parameters
and doing a COMMIT inside the procedure.  When a CALL has output
parameters, the portal uses the strategy PORTAL_UTIL_SELECT instead of
PORTAL_MULTI_QUERY.  Using PORTAL_UTIL_SELECT causes the portal's
snapshot to be registered with the current resource
owner (portal->holdSnapshot); see
9ee1cf04ab6bcefe03a11837b53f29ca9dc24c7a for the reason.

Normally, PortalDrop() unregisters the snapshot.  If not, then
ResourceOwnerRelease() will print a warning about a snapshot leak on
transaction commit.  A transaction commit normally drops all
portals (PreCommit_Portals()), except the active portal.  So in case of
the active portal, we need to manually release the snapshot to avoid the
warning.

Reported-by: Prabhat Sahu <prabhat.sahu@enterprisedb.com>
Reviewed-by: Jonathan S. Katz <jkatz@postgresql.org>

src/backend/utils/mmgr/portalmem.c

@@ -689,13 +689,23 @@ PreCommit_Portals(bool isPrepare)
 
 		/*
 		 * Do not touch active portals --- this can only happen in the case of
-		 * a multi-transaction utility command, such as VACUUM.
+		 * a multi-transaction utility command, such as VACUUM, or a commit in
+		 * a procedure.
 		 *
 		 * Note however that any resource owner attached to such a portal is
-		 * still going to go away, so don't leave a dangling pointer.
+		 * still going to go away, so don't leave a dangling pointer.  Also
+		 * unregister any snapshots held by the portal, mainly to avoid
+		 * snapshot leak warnings from ResourceOwnerRelease().
 		 */
 		if (portal->status == PORTAL_ACTIVE)
 		{
+			if (portal->holdSnapshot)
+			{
+				if (portal->resowner)
+					UnregisterSnapshotFromOwner(portal->holdSnapshot,
+												portal->resowner);
+				portal->holdSnapshot = NULL;
+			}
 			portal->resowner = NULL;
 			continue;
 		}

src/pl/plpgsql/src/expected/plpgsql_transaction.out

@@ -463,6 +463,36 @@ SELECT * FROM test2;
  42
 (1 row)
 
+-- Test transaction in procedure with output parameters.  This uses a
+-- different portal strategy and different code paths in pquery.c.
+CREATE PROCEDURE transaction_test10a(INOUT x int)
+LANGUAGE plpgsql
+AS $$
+BEGIN
+  x := x + 1;
+  COMMIT;
+END;
+$$;
+CALL transaction_test10a(10);
+ x  
+----
+ 11
+(1 row)
+
+CREATE PROCEDURE transaction_test10b(INOUT x int)
+LANGUAGE plpgsql
+AS $$
+BEGIN
+  x := x - 1;
+  ROLLBACK;
+END;
+$$;
+CALL transaction_test10b(10);
+ x 
+---
+ 9
+(1 row)
+
 DROP TABLE test1;
 DROP TABLE test2;
 DROP TABLE test3;

src/pl/plpgsql/src/sql/plpgsql_transaction.sql

@@ -387,6 +387,31 @@ $$;
 SELECT * FROM test2;
 
 
+-- Test transaction in procedure with output parameters.  This uses a
+-- different portal strategy and different code paths in pquery.c.
+CREATE PROCEDURE transaction_test10a(INOUT x int)
+LANGUAGE plpgsql
+AS $$
+BEGIN
+  x := x + 1;
+  COMMIT;
+END;
+$$;
+
+CALL transaction_test10a(10);
+
+CREATE PROCEDURE transaction_test10b(INOUT x int)
+LANGUAGE plpgsql
+AS $$
+BEGIN
+  x := x - 1;
+  ROLLBACK;
+END;
+$$;
+
+CALL transaction_test10b(10);
+
+
 DROP TABLE test1;
 DROP TABLE test2;
 DROP TABLE test3;