Simplify restriction handling of two-phase commit for temporary objects

There were two flags used to track the access to temporary tables and
to the temporary namespace of a session which are used to restrict
PREPARE TRANSACTION, however the first control flag is a concept
included in the second.  This removes the flag for temporary table
tracking, keeping around only the one at namespace level.

Author: Michael Paquier
Reviewed-by: Álvaro Herrera
Discussion: https://postgr.es/m/20190118053126.GH1883@paquier.xyz

src/backend/access/common/relation.c

@@ -71,7 +71,7 @@ relation_open(Oid relationId, LOCKMODE lockmode)
 
 	/* Make note that we've accessed a temporary relation */
 	if (RelationUsesLocalBuffers(r))
-		MyXactFlags |= XACT_FLAGS_ACCESSEDTEMPREL;
+		MyXactFlags |= XACT_FLAGS_ACCESSEDTEMPNAMESPACE;
 
 	pgstat_initstats(r);
 
@@ -121,7 +121,7 @@ try_relation_open(Oid relationId, LOCKMODE lockmode)
 
 	/* Make note that we've accessed a temporary relation */
 	if (RelationUsesLocalBuffers(r))
-		MyXactFlags |= XACT_FLAGS_ACCESSEDTEMPREL;
+		MyXactFlags |= XACT_FLAGS_ACCESSEDTEMPNAMESPACE;
 
 	pgstat_initstats(r);
 

src/backend/access/transam/xact.c

@@ -2266,6 +2266,11 @@ PrepareTransaction(void)
 	 * clean up the source backend's local buffers and ON COMMIT state if the
 	 * prepared xact includes a DROP of a temp table.
 	 *
+	 * Other objects types, like functions, operators or extensions, share the
+	 * same restriction as they should not be created, locked or dropped as
+	 * this can mess up with this session or even a follow-up session trying
+	 * to use the same temporary namespace.
+	 *
 	 * We must check this after executing any ON COMMIT actions, because they
 	 * might still access a temp relation.
 	 *
@@ -2273,22 +2278,10 @@ PrepareTransaction(void)
 	 * cases, such as a temp table created and dropped all within the
 	 * transaction.  That seems to require much more bookkeeping though.
 	 */
-	if ((MyXactFlags & XACT_FLAGS_ACCESSEDTEMPREL))
-		ereport(ERROR,
-				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("cannot PREPARE a transaction that has operated on temporary tables")));
-
-	/*
-	 * Similarly, PREPARE TRANSACTION is not allowed if the temporary
-	 * namespace has been involved in this transaction as we cannot allow it
-	 * to create, lock, or even drop objects within the temporary namespace
-	 * as this can mess up with this session or even a follow-up session
-	 * trying to use the same temporary namespace.
-	 */
 	if ((MyXactFlags & XACT_FLAGS_ACCESSEDTEMPNAMESPACE))
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("cannot PREPARE a transaction that has operated on temporary namespace")));
+				 errmsg("cannot PREPARE a transaction that has operated on temporary objects")));
 
 	/*
 	 * Likewise, don't allow PREPARE after pg_export_snapshot.  This could be

src/backend/commands/lockcmds.c

@@ -108,7 +108,7 @@ RangeVarCallbackForLockTable(const RangeVar *rv, Oid relid, Oid oldrelid,
 	 */
 	relpersistence = get_rel_persistence(relid);
 	if (relpersistence == RELPERSISTENCE_TEMP)
-		MyXactFlags |= XACT_FLAGS_ACCESSEDTEMPREL;
+		MyXactFlags |= XACT_FLAGS_ACCESSEDTEMPNAMESPACE;
 
 	/* Check permissions. */
 	aclresult = LockTableAclCheck(relid, lockmode, GetUserId());

src/backend/commands/tablecmds.c

@@ -13642,7 +13642,7 @@ PreCommit_on_commit_actions(void)
 				 * relations, we can skip truncating ON COMMIT DELETE ROWS
 				 * tables, as they must still be empty.
 				 */
-				if ((MyXactFlags & XACT_FLAGS_ACCESSEDTEMPREL))
+				if ((MyXactFlags & XACT_FLAGS_ACCESSEDTEMPNAMESPACE))
 					oids_to_truncate = lappend_oid(oids_to_truncate, oc->relid);
 				break;
 			case ONCOMMIT_DROP:

src/include/access/xact.h

@@ -87,10 +87,10 @@ extern int	synchronous_commit;
 extern int	MyXactFlags;
 
 /*
- * XACT_FLAGS_ACCESSEDTEMPREL - set when a temporary relation is accessed. We
+ * XACT_FLAGS_ACCESSEDTEMPNAMESPACE - set when a temporary object is accessed.
- * don't allow PREPARE TRANSACTION in that case.
+ * We don't allow PREPARE TRANSACTION in that case.
  */
-#define XACT_FLAGS_ACCESSEDTEMPREL				(1U << 0)
+#define XACT_FLAGS_ACCESSEDTEMPNAMESPACE		(1U << 0)
 
 /*
  * XACT_FLAGS_ACQUIREDACCESSEXCLUSIVELOCK - records whether the top level xact
@@ -98,12 +98,6 @@ extern int	MyXactFlags;
  */
 #define XACT_FLAGS_ACQUIREDACCESSEXCLUSIVELOCK	(1U << 1)
 
-/*
- * XACT_FLAGS_ACCESSEDTEMPNAMESPACE - set when a temporary namespace is
- * accessed.  We don't allow PREPARE TRANSACTION in that case.
- */
-#define XACT_FLAGS_ACCESSEDTEMPNAMESPACE		(1U << 2)
-
 /*
  *	start- and end-of-transaction callbacks for dynamically loaded modules
  */

src/test/modules/test_extensions/expected/test_extensions.out

@@ -148,7 +148,7 @@ SELECT create_extension_with_temp_schema();
 (1 row)
 
 PREPARE TRANSACTION 'twophase_extension';
-ERROR:  cannot PREPARE a transaction that has operated on temporary namespace
+ERROR:  cannot PREPARE a transaction that has operated on temporary objects
 -- Clean up
 DROP TABLE test_ext4_tab;
 DROP FUNCTION create_extension_with_temp_schema();

src/test/regress/expected/temp.out

@@ -310,32 +310,32 @@ begin;
 create function pg_temp.twophase_func() returns void as
   $$ select '2pc_func'::text $$ language sql;
 prepare transaction 'twophase_func';
-ERROR:  cannot PREPARE a transaction that has operated on temporary namespace
+ERROR:  cannot PREPARE a transaction that has operated on temporary objects
 -- Function drop
 create function pg_temp.twophase_func() returns void as
   $$ select '2pc_func'::text $$ language sql;
 begin;
 drop function pg_temp.twophase_func();
 prepare transaction 'twophase_func';
-ERROR:  cannot PREPARE a transaction that has operated on temporary namespace
+ERROR:  cannot PREPARE a transaction that has operated on temporary objects
 -- Operator creation
 begin;
 create operator pg_temp.@@ (leftarg = int4, rightarg = int4, procedure = int4mi);
 prepare transaction 'twophase_operator';
-ERROR:  cannot PREPARE a transaction that has operated on temporary namespace
+ERROR:  cannot PREPARE a transaction that has operated on temporary objects
 -- These generate errors about temporary tables.
 begin;
 create type pg_temp.twophase_type as (a int);
 prepare transaction 'twophase_type';
-ERROR:  cannot PREPARE a transaction that has operated on temporary tables
+ERROR:  cannot PREPARE a transaction that has operated on temporary objects
 begin;
 create view pg_temp.twophase_view as select 1;
 prepare transaction 'twophase_view';
-ERROR:  cannot PREPARE a transaction that has operated on temporary tables
+ERROR:  cannot PREPARE a transaction that has operated on temporary objects
 begin;
 create sequence pg_temp.twophase_seq;
 prepare transaction 'twophase_sequence';
-ERROR:  cannot PREPARE a transaction that has operated on temporary tables
+ERROR:  cannot PREPARE a transaction that has operated on temporary objects
 -- Temporary tables cannot be used with two-phase commit.
 create temp table twophase_tab (a int);
 begin;
@@ -345,19 +345,19 @@ select a from twophase_tab;
 (0 rows)
 
 prepare transaction 'twophase_tab';
-ERROR:  cannot PREPARE a transaction that has operated on temporary tables
+ERROR:  cannot PREPARE a transaction that has operated on temporary objects
 begin;
 insert into twophase_tab values (1);
 prepare transaction 'twophase_tab';
-ERROR:  cannot PREPARE a transaction that has operated on temporary tables
+ERROR:  cannot PREPARE a transaction that has operated on temporary objects
 begin;
 lock twophase_tab in access exclusive mode;
 prepare transaction 'twophase_tab';
-ERROR:  cannot PREPARE a transaction that has operated on temporary tables
+ERROR:  cannot PREPARE a transaction that has operated on temporary objects
 begin;
 drop table twophase_tab;
 prepare transaction 'twophase_tab';
-ERROR:  cannot PREPARE a transaction that has operated on temporary tables
+ERROR:  cannot PREPARE a transaction that has operated on temporary objects
 -- Corner case: current_schema may create a temporary schema if namespace
 -- creation is pending, so check after that.  First reset the connection
 -- to remove the temporary namespace, and make sure that non-parallel plans
@@ -374,4 +374,4 @@ SELECT current_schema() ~ 'pg_temp' AS is_temp_schema;
 (1 row)
 
 PREPARE TRANSACTION 'twophase_search';
-ERROR:  cannot PREPARE a transaction that has operated on temporary namespace
+ERROR:  cannot PREPARE a transaction that has operated on temporary objects