PortalRun must guard against the possibility that the portal it's

running contains VACUUM or a similar command that will internally start
and commit transactions.  In such a case, the original caller values of
CurrentMemoryContext and CurrentResourceOwner will point to objects that
will be destroyed by the internal commit.  We must restore these pointers
to point to the newly-manufactured transaction context and resource owner,
rather than possibly pointing to deleted memory.
Also tweak xact.c so that AbortTransaction and AbortSubTransaction
forcibly restore a sane value for CurrentResourceOwner, much as they
have always done for CurrentMemoryContext.  I'm not certain this is
necessary but I'm feeling paranoid today.
Responds to Sean Chittenden's bug report of 4-Oct.

src/backend/access/transam/xact.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.190 2004/09/16 20:17:16 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.191 2004/10/04 21:52:14 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -205,6 +205,7 @@ static void AssignSubTransactionId(TransactionState s);
 static void AbortTransaction(void);
 static void AtAbort_Memory(void);
 static void AtCleanup_Memory(void);
+static void AtAbort_ResourceOwner(void);
 static void AtCommit_LocalCache(void);
 static void AtCommit_Memory(void);
 static void AtStart_Cache(void);
@@ -229,6 +230,7 @@ static void PopTransaction(void);
 
 static void AtSubAbort_Memory(void);
 static void AtSubCleanup_Memory(void);
+static void AtSubAbort_ResourceOwner(void);
 static void AtSubCommit_Memory(void);
 static void AtSubStart_Memory(void);
 static void AtSubStart_ResourceOwner(void);
@@ -1103,7 +1105,6 @@ AtAbort_Memory(void)
 		MemoryContextSwitchTo(TopMemoryContext);
 }
 
-
 /*
  * AtSubAbort_Memory
  */
@@ -1115,6 +1116,33 @@ AtSubAbort_Memory(void)
 	MemoryContextSwitchTo(TopTransactionContext);
 }
 
+
+/*
+ *	AtAbort_ResourceOwner
+ */
+static void
+AtAbort_ResourceOwner(void)
+{
+	/*
+	 * Make sure we have a valid ResourceOwner, if possible (else it
+	 * will be NULL, which is OK)
+	 */
+	CurrentResourceOwner = TopTransactionResourceOwner;
+}
+
+/*
+ * AtSubAbort_ResourceOwner
+ */
+static void
+AtSubAbort_ResourceOwner(void)
+{
+	TransactionState s = CurrentTransactionState;
+
+	/* Make sure we have a valid ResourceOwner */
+	CurrentResourceOwner = s->curTransactionOwner;
+}
+
+
 /*
  * AtSubAbort_childXids
  */
@@ -1598,8 +1626,9 @@ AbortTransaction(void)
 	 */
 	s->state = TRANS_ABORT;
 
-	/* Make sure we are in a valid memory context */
+	/* Make sure we have a valid memory context and resource owner */
 	AtAbort_Memory();
+	AtAbort_ResourceOwner();
 
 	/*
 	 * Reset user id which might have been changed transiently.  We cannot
@@ -3338,6 +3367,7 @@ AbortSubTransaction(void)
 	 * do abort processing
 	 */
 	AtSubAbort_Memory();
+	AtSubAbort_ResourceOwner();
 
 	/*
 	 * We can skip all this stuff if the subxact failed before creating

src/backend/tcop/pquery.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/tcop/pquery.c,v 1.87 2004/09/13 20:07:05 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/tcop/pquery.c,v 1.88 2004/10/04 21:52:15 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -491,12 +491,14 @@ PortalRun(Portal portal, long count,
 		  char *completionTag)
 {
 	bool		result;
+	ResourceOwner saveTopTransactionResourceOwner;
+	MemoryContext saveTopTransactionContext;
 	Portal		saveActivePortal;
 	Snapshot	saveActiveSnapshot;
 	ResourceOwner saveResourceOwner;
 	MemoryContext savePortalContext;
 	MemoryContext saveQueryContext;
-	MemoryContext oldContext;
+	MemoryContext saveMemoryContext;
 
 	AssertArg(PortalIsValid(portal));
 
@@ -523,12 +525,26 @@ PortalRun(Portal portal, long count,
 
 	/*
 	 * Set up global portal context pointers.
+	 *
+	 * We have to play a special game here to support utility commands like
+	 * VACUUM and CLUSTER, which internally start and commit transactions.
+	 * When we are called to execute such a command, CurrentResourceOwner
+	 * will be pointing to the TopTransactionResourceOwner --- which will
+	 * be destroyed and replaced in the course of the internal commit and
+	 * restart.  So we need to be prepared to restore it as pointing to
+	 * the exit-time TopTransactionResourceOwner.  (Ain't that ugly?  This
+	 * idea of internally starting whole new transactions is not good.)
+	 * CurrentMemoryContext has a similar problem, but the other pointers
+	 * we save here will be NULL or pointing to longer-lived objects.
 	 */
+	saveTopTransactionResourceOwner = TopTransactionResourceOwner;
+	saveTopTransactionContext = TopTransactionContext;
 	saveActivePortal = ActivePortal;
 	saveActiveSnapshot = ActiveSnapshot;
 	saveResourceOwner = CurrentResourceOwner;
 	savePortalContext = PortalContext;
 	saveQueryContext = QueryContext;
+	saveMemoryContext = CurrentMemoryContext;
 	PG_TRY();
 	{
 		ActivePortal = portal;
@@ -537,7 +553,7 @@ PortalRun(Portal portal, long count,
 		PortalContext = PortalGetHeapMemory(portal);
 		QueryContext = portal->queryContext;
 
-		oldContext = MemoryContextSwitchTo(PortalContext);
+		MemoryContextSwitchTo(PortalContext);
 
 		switch (portal->strategy)
 		{
@@ -620,9 +636,16 @@ PortalRun(Portal portal, long count,
 		portal->status = PORTAL_FAILED;
 
 		/* Restore global vars and propagate error */
+		if (saveMemoryContext == saveTopTransactionContext)
+			MemoryContextSwitchTo(TopTransactionContext);
+		else
+			MemoryContextSwitchTo(saveMemoryContext);
 		ActivePortal = saveActivePortal;
 		ActiveSnapshot = saveActiveSnapshot;
-		CurrentResourceOwner = saveResourceOwner;
+		if (saveResourceOwner == saveTopTransactionResourceOwner)
+			CurrentResourceOwner = TopTransactionResourceOwner;
+		else
+			CurrentResourceOwner = saveResourceOwner;
 		PortalContext = savePortalContext;
 		QueryContext = saveQueryContext;
 
@@ -630,11 +653,16 @@ PortalRun(Portal portal, long count,
 	}
 	PG_END_TRY();
 
-	MemoryContextSwitchTo(oldContext);
-
+	if (saveMemoryContext == saveTopTransactionContext)
+		MemoryContextSwitchTo(TopTransactionContext);
+	else
+		MemoryContextSwitchTo(saveMemoryContext);
 	ActivePortal = saveActivePortal;
 	ActiveSnapshot = saveActiveSnapshot;
-	CurrentResourceOwner = saveResourceOwner;
+	if (saveResourceOwner == saveTopTransactionResourceOwner)
+		CurrentResourceOwner = TopTransactionResourceOwner;
+	else
+		CurrentResourceOwner = saveResourceOwner;
 	PortalContext = savePortalContext;
 	QueryContext = saveQueryContext;