### Eclipse Workspace Patch 1.0
#P Postgres-HEAD
Index: src/backend/access/heap/heapam.c
===================================================================
RCS file: /root/cvsrepo/pgsql/src/backend/access/heap/heapam.c,v
retrieving revision 1.264
diff -u -r1.264 heapam.c
--- src/backend/access/heap/heapam.c	30 Sep 2008 10:52:10 -0000	1.264
+++ src/backend/access/heap/heapam.c	8 Oct 2008 01:53:44 -0000
@@ -878,7 +878,7 @@
 
 	/* Make note that we've accessed a temporary relation */
 	if (r->rd_istemp)
-		MyXactAccessedTempRel = true;
+		enlistRelationIdFor2PCChecks(relationId);
 
 	pgstat_initstats(r);
 
@@ -926,7 +926,7 @@
 
 	/* Make note that we've accessed a temporary relation */
 	if (r->rd_istemp)
-		MyXactAccessedTempRel = true;
+		enlistRelationIdFor2PCChecks(relationId);
 
 	pgstat_initstats(r);
 
@@ -976,7 +976,7 @@
 
 	/* Make note that we've accessed a temporary relation */
 	if (r->rd_istemp)
-		MyXactAccessedTempRel = true;
+		enlistRelationIdFor2PCChecks(relationId);
 
 	pgstat_initstats(r);
 
Index: src/backend/access/transam/xact.c
===================================================================
RCS file: /root/cvsrepo/pgsql/src/backend/access/transam/xact.c,v
retrieving revision 1.265
diff -u -r1.265 xact.c
--- src/backend/access/transam/xact.c	11 Aug 2008 11:05:10 -0000	1.265
+++ src/backend/access/transam/xact.c	8 Oct 2008 01:53:44 -0000
@@ -47,6 +47,7 @@
 #include "utils/memutils.h"
 #include "utils/relcache.h"
 #include "utils/snapmgr.h"
+#include "utils/tqual.h"
 #include "utils/xml.h"
 #include "pg_trace.h"
 
@@ -65,13 +66,6 @@
 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
@@ -209,6 +203,9 @@
  */
 static MemoryContext TransactionAbortContext = NULL;
 
+/* Hash table containing Oids of accessed temporary relations */
+HTAB	*accessedTempRel;
+
 /*
  * List of add-on start- and end-of-xact callbacks
  */
@@ -1511,7 +1508,6 @@
 	XactIsoLevel = DefaultXactIsoLevel;
 	XactReadOnly = DefaultXactReadOnly;
 	forceSyncCommit = false;
-	MyXactAccessedTempRel = false;
 
 	/*
 	 * reinitialize within-transaction counters
@@ -1777,6 +1773,36 @@
 	RESUME_INTERRUPTS();
 }
 
+/* ----------------
+ * 	enlistRelationIdFor2PCChecks - enlist a relation in the list of
+ *  	resources to check at PREPARE COMMIT time if we are part of
+ *  	a 2PC transaction. The resource will be removed from the list
+ *  	if the table is dropped before commit.
+ * ----------------
+ */
+void
+enlistRelationIdFor2PCChecks(Oid relationId)
+{
+	/*
+	 * Each time a temporary relation is accessed, it is added to the
+	 * accessedTempRel list. PREPARE TRANSACTION will fail if any
+	 * of the accessed relation is still valid (not dropped).  (This is
+	 * called from from heapam.c.)
+	 */
+	if (accessedTempRel == NULL)
+	{ // Allocate the list on-demand
+		HASHCTL ctl;
+
+		ctl.keysize = sizeof(Oid);
+		ctl.entrysize = sizeof(Oid);
+		accessedTempRel = hash_create("accessed temp tables", 4, &ctl,
+				HASH_ELEM);
+	}
+
+	// Add to the hash list if missing
+	Oid *tid = hash_search(accessedTempRel, &relationId, HASH_ENTER, NULL);
+	*tid = relationId;
+}
 
 /*
  *	PrepareTransaction
@@ -1853,14 +1879,45 @@
 	 * 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.
+	 * We only allow to proceed further if the accessed temp tables have
+	 * been dropped before PREPARE COMMIT.
 	 */
-	if (MyXactAccessedTempRel)
-		ereport(ERROR,
-				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("cannot PREPARE a transaction that has operated on temporary tables")));
+	if (accessedTempRel != NULL)
+	{
+		HASH_SEQ_STATUS	status;
+		Oid*			tempTableOid;
+
+		/* Prevent further updates to the list as recommended in hash_seq_init doc. */
+		hash_freeze(accessedTempRel);
+		hash_seq_init(&status, accessedTempRel);
+		while ((tempTableOid = (Oid *) hash_seq_search(&status)) != NULL)
+		{ /* Check all accessed temp tables. If the table has been dropped,
+		   * try_relation_open will fail and we can safely continue. */
+			Relation tempTable = try_relation_open(*tempTableOid, NoLock);
+			if (tempTable != NULL)
+			{ /* We have an open temp table at PREPARE COMMIT time. We
+			   * will only accept empty temp tables and throw an error
+			   * in other cases. */
+				HeapScanDesc scan;
+				HeapTuple tuple;
+				scan = heap_beginscan(tempTable, SnapshotNow, 0, NULL);
+				if ((tuple = heap_getnext(scan, ForwardScanDirection)) != NULL)
+				{
+					hash_seq_term(&status);
+					hash_destroy(accessedTempRel);
+					accessedTempRel = NULL;
+					ereport(ERROR,
+							(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+									errmsg("cannot PREPARE a transaction that has operated on temporary tables that are not empty at commit time")));
+				}
+				heap_endscan(scan);
+				relation_close(tempTable, NoLock);
+			}
+		}
+		hash_seq_term(&status);
+		hash_destroy(accessedTempRel);
+		accessedTempRel = NULL;
+	}
 
 	/* Prevent cancel/die interrupt while cleaning up */
 	HOLD_INTERRUPTS();
@@ -2151,6 +2208,12 @@
 		elog(FATAL, "CleanupTransaction: unexpected state %s",
 			 TransStateAsString(s->state));
 
+	if (accessedTempRel != NULL)
+	{
+		hash_destroy(accessedTempRel);
+		accessedTempRel = NULL;
+	}
+
 	/*
 	 * do abort cleanup processing
 	 */
Index: src/include/access/xact.h
===================================================================
RCS file: /root/cvsrepo/pgsql/src/include/access/xact.h,v
retrieving revision 1.95
diff -u -r1.95 xact.h
--- src/include/access/xact.h	11 Aug 2008 11:05:11 -0000	1.95
+++ src/include/access/xact.h	8 Oct 2008 01:53:44 -0000
@@ -18,6 +18,7 @@
 #include "nodes/pg_list.h"
 #include "storage/relfilenode.h"
 #include "utils/timestamp.h"
+#include "postgres_ext.h"
 
 
 /*
@@ -44,8 +45,8 @@
 /* Asynchronous commits */
 extern bool XactSyncCommit;
 
-/* Kluge for 2PC support */
-extern bool MyXactAccessedTempRel;
+/* List of temp tables accessed during a transaction for 2PC support */
+extern void enlistRelationIdFor2PCChecks(Oid relationId);
 
 /*
  *	start- and end-of-transaction callbacks for dynamically loaded modules