Fix PREPARE TRANSACTION to reject the case where the transaction has dropped a

temporary table; we can't support that because there's no way to clean up the
source backend's internal state if the eventual COMMIT PREPARED is done by
another backend.  This was checked correctly in 8.1 but I broke it in 8.2 :-(.
Patch by Heikki Linnakangas, original trouble report by John Smith.

src/backend/access/heap/heapam.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.249 2008/01/30 18:35:55 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.250 2008/03/04 19:54:06 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -868,6 +868,10 @@ relation_open(Oid relationId, LOCKMODE lockmode)
 	if (!RelationIsValid(r))
 		elog(ERROR, "could not open relation with OID %u", relationId);
 
+	/* Make note that we've accessed a temporary relation */
+	if (r->rd_istemp)
+		MyXactAccessedTempRel = true;
+
 	pgstat_initstats(r);
 
 	return r;
@@ -912,6 +916,10 @@ try_relation_open(Oid relationId, LOCKMODE lockmode)
 	if (!RelationIsValid(r))
 		elog(ERROR, "could not open relation with OID %u", relationId);
 
+	/* Make note that we've accessed a temporary relation */
+	if (r->rd_istemp)
+		MyXactAccessedTempRel = true;
+
 	pgstat_initstats(r);
 
 	return r;
@@ -958,6 +966,10 @@ relation_open_nowait(Oid relationId, LOCKMODE lockmode)
 	if (!RelationIsValid(r))
 		elog(ERROR, "could not open relation with OID %u", relationId);
 
+	/* Make note that we've accessed a temporary relation */
+	if (r->rd_istemp)
+		MyXactAccessedTempRel = true;
+
 	pgstat_initstats(r);
 
 	return r;

src/backend/access/transam/xact.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.257 2008/01/15 18:56:59 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.258 2008/03/04 19:54:06 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -62,6 +62,13 @@ bool		XactSyncCommit = true;
 int			CommitDelay = 0;	/* precommit delay in microseconds */
 int			CommitSiblings = 5; /* # concurrent xacts needed to sleep */
 
+/*
+ * MyXactAccessedTempRel is set when a temporary relation is accessed.
+ * We don't allow PREPARE TRANSACTION in that case.  (This is global
+ * so that it can be set from heapam.c.)
+ */
+bool		MyXactAccessedTempRel = false;
+
 
 /*
  *	transaction states - transaction state from server perspective
@@ -1445,6 +1452,7 @@ StartTransaction(void)
 	XactIsoLevel = DefaultXactIsoLevel;
 	XactReadOnly = DefaultXactReadOnly;
 	forceSyncCommit = false;
+	MyXactAccessedTempRel = false;
 
 	/*
 	 * reinitialize within-transaction counters
@@ -1770,6 +1778,26 @@ PrepareTransaction(void)
 
 	/* NOTIFY and flatfiles will be handled below */
 
+	/*
+	 * Don't allow PREPARE TRANSACTION if we've accessed a temporary table
+	 * 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.
+	 *
+	 * We must check this after executing any ON COMMIT actions, because
+	 * they might still access a temp relation.
+	 *
+	 * XXX In principle this could be relaxed to allow some useful special
+	 * cases, such as a temp table created and dropped all within the
+	 * transaction.  That seems to require much more bookkeeping though.
+	 */
+	if (MyXactAccessedTempRel)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("cannot PREPARE a transaction that has operated on temporary tables")));
+
 	/* Prevent cancel/die interrupt while cleaning up */
 	HOLD_INTERRUPTS();
 

src/backend/storage/lmgr/lmgr.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/lmgr.c,v 1.96 2008/01/08 23:18:50 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/lmgr.c,v 1.97 2008/03/04 19:54:06 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -19,12 +19,10 @@
 #include "access/transam.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
-#include "catalog/namespace.h"
 #include "miscadmin.h"
 #include "storage/lmgr.h"
 #include "storage/procarray.h"
 #include "utils/inval.h"
-#include "utils/lsyscache.h"
 
 
 /*
@@ -663,44 +661,6 @@ UnlockSharedObject(Oid classid, Oid objid, uint16 objsubid,
 }
 
 
-/*
- * LockTagIsTemp
- *		Determine whether a locktag is for a lock on a temporary object
- *
- * We need this because 2PC cannot deal with temp objects
- */
-bool
-LockTagIsTemp(const LOCKTAG *tag)
-{
-	switch ((LockTagType) tag->locktag_type)
-	{
-		case LOCKTAG_RELATION:
-		case LOCKTAG_RELATION_EXTEND:
-		case LOCKTAG_PAGE:
-		case LOCKTAG_TUPLE:
-			/* check for lock on a temp relation */
-			/* field1 is dboid, field2 is reloid for all of these */
-			if ((Oid) tag->locktag_field1 == InvalidOid)
-				return false;	/* shared, so not temp */
-			if (isTempOrToastNamespace(get_rel_namespace((Oid) tag->locktag_field2)))
-				return true;
-			break;
-		case LOCKTAG_TRANSACTION:
-		case LOCKTAG_VIRTUALTRANSACTION:
-			/* there are no temp transactions */
-			break;
-		case LOCKTAG_OBJECT:
-			/* there are currently no non-table temp objects */
-			break;
-		case LOCKTAG_USERLOCK:
-		case LOCKTAG_ADVISORY:
-			/* assume these aren't temp */
-			break;
-	}
-	return false;				/* default case */
-}
-
-
 /*
  * Append a description of a lockable object to buf.
  *

src/backend/storage/lmgr/lock.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/lock.c,v 1.181 2008/02/02 22:26:17 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/lmgr/lock.c,v 1.182 2008/03/04 19:54:06 tgl Exp $
  *
  * NOTES
  *	  A lock table is a shared memory hash table.  When
@@ -37,7 +37,6 @@
 #include "access/twophase_rmgr.h"
 #include "miscadmin.h"
 #include "pgstat.h"
-#include "storage/lmgr.h"
 #include "utils/memutils.h"
 #include "utils/ps_status.h"
 #include "utils/resowner.h"
@@ -1871,12 +1870,6 @@ AtPrepare_Locks(void)
 				elog(ERROR, "cannot PREPARE when session locks exist");
 		}
 
-		/* Can't handle it if the lock is on a temporary object */
-		if (LockTagIsTemp(&locallock->tag.lock))
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("cannot PREPARE a transaction that has operated on temporary tables")));
-
 		/*
 		 * Create a 2PC record.
 		 */

src/include/access/xact.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/xact.h,v 1.93 2008/01/01 19:45:56 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/access/xact.h,v 1.94 2008/03/04 19:54:06 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -44,6 +44,9 @@ extern bool XactReadOnly;
 /* Asynchronous commits */
 extern bool XactSyncCommit;
 
+/* Kluge for 2PC support */
+extern bool MyXactAccessedTempRel;
+
 /*
  *	start- and end-of-transaction callbacks for dynamically loaded modules
  */

src/include/storage/lmgr.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/storage/lmgr.h,v 1.60 2008/01/01 19:45:59 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/storage/lmgr.h,v 1.61 2008/03/04 19:54:06 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -72,9 +72,6 @@ extern void LockSharedObject(Oid classid, Oid objid, uint16 objsubid,
 extern void UnlockSharedObject(Oid classid, Oid objid, uint16 objsubid,
 				   LOCKMODE lockmode);
 
-/* Knowledge about which locktags describe temp objects */
-extern bool LockTagIsTemp(const LOCKTAG *tag);
-
 /* Describe a locktag for error messages */
 extern void DescribeLockTag(StringInfo buf, const LOCKTAG *tag);