0001-Simplify-2PC-restriction-handling-for-temporary-obje.patch

From 52c23f7a3f63dffa57d57ceeac7c1e2ef5ba68ad Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Wed, 16 Jan 2019 10:34:13 +0900
Subject: [PATCH] Simplify 2PC restriction handling for temporary objects

There are two flags used to control access to temporary tables and
access to the temporary namespace of a session, however the first
control flag is actually a concept included in the second.  This removes
the flag for temporary table tracking, keeping around only the one at
namespace level.
---
 src/backend/access/heap/heapam.c   |  4 ++--
 src/backend/access/transam/xact.c  | 19 ++++++-------------
 src/backend/commands/lockcmds.c    |  2 +-
 src/backend/commands/tablecmds.c   |  2 +-
 src/include/access/xact.h          | 12 +++---------
 src/test/regress/expected/temp.out | 14 +++++++-------
 6 files changed, 20 insertions(+), 33 deletions(-)

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 9afbc8228d..dd54810052 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -1144,7 +1144,7 @@ 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);
 
@@ -1194,7 +1194,7 @@ 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);
 
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 18467d96d2..0c20729c68 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -2259,13 +2259,18 @@ PrepareTransaction(void)
 	/* NOTIFY will be handled below */
 
 	/*
-	 * Don't allow PREPARE TRANSACTION if we've accessed a temporary table in
+	 * Don't allow PREPARE TRANSACTION if we've accessed a temporary object in
 	 * this transaction.  Having the prepared xact hold locks on another
 	 * backend's temp table seems a bad idea --- for instance it would prevent
 	 * the backend from exiting.  There are other problems too, such as how to
 	 * 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.
 	 *
@@ -2273,18 +2278,6 @@ 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),
diff --git a/src/backend/commands/lockcmds.c b/src/backend/commands/lockcmds.c
index 4cd7ec2d5f..bea99b59a2 100644
--- a/src/backend/commands/lockcmds.c
+++ b/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());
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index d2781cbf19..79b0a0d6e8 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -13253,7 +13253,7 @@ 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:
diff --git a/src/include/access/xact.h b/src/include/access/xact.h
index ed21a13896..ae89920687 100644
--- a/src/include/access/xact.h
+++ b/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
- * don't allow PREPARE TRANSACTION in that case.
+ * XACT_FLAGS_ACCESSEDTEMPNAMESPACE - set when a temporary namespace is
+ * accessed.  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
  */
diff --git a/src/test/regress/expected/temp.out b/src/test/regress/expected/temp.out
index d6d8f25141..b1dfe6499f 100644
--- a/src/test/regress/expected/temp.out
+++ b/src/test/regress/expected/temp.out
@@ -327,15 +327,15 @@ ERROR:  cannot PREPARE a transaction that has operated on temporary namespace
 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 namespace
 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 namespace
 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 namespace
 -- 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 namespace
 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 namespace
 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 namespace
 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 namespace
 -- 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
-- 
2.20.1