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

4 files changed, 10 insertions, 17 deletions

diff --git a/src/backend/access/common/relation.c b/src/backend/access/common/relation.c
index beec34f126f..41a0051f88e 100644
--- a/src/backend/access/common/relation.c
+++ b/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);
 
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 7c3a9c1e899..0181976964c 100644
--- a/src/backend/access/transam/xact.c
+++ b/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
diff --git a/src/backend/commands/lockcmds.c b/src/backend/commands/lockcmds.c
index f4da564e012..43bba717f22 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 36fdcc0d52c..9daf3e6588f 100644
--- a/src/backend/commands/tablecmds.c
+++ b/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: