diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index e375fb4dae..bb1a2077ff 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -13,7 +13,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.394 2009/10/26 02:26:29 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/vacuum.c,v 1.395 2009/11/10 18:00:06 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -217,10 +217,10 @@ static List *get_rel_oids(Oid relid, const RangeVar *vacrel,
 static void vac_truncate_clog(TransactionId frozenXID);
 static void vacuum_rel(Oid relid, VacuumStmt *vacstmt, bool do_toast,
 		   bool for_wraparound, bool *scanned_all);
-static void full_vacuum_rel(Relation onerel, VacuumStmt *vacstmt);
+static bool full_vacuum_rel(Relation onerel, VacuumStmt *vacstmt);
 static void scan_heap(VRelStats *vacrelstats, Relation onerel,
 		  VacPageList vacuum_pages, VacPageList fraged_pages);
-static void repair_frag(VRelStats *vacrelstats, Relation onerel,
+static bool repair_frag(VRelStats *vacrelstats, Relation onerel,
 			VacPageList vacuum_pages, VacPageList fraged_pages,
 			int nindexes, Relation *Irel);
 static void move_chain_tuple(Relation rel,
@@ -1020,6 +1020,7 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, bool do_toast, bool for_wraparound,
 	Oid			toast_relid;
 	Oid			save_userid;
 	bool		save_secdefcxt;
+	bool		heldoff;
 
 	if (scanned_all)
 		*scanned_all = false;
@@ -1186,9 +1187,9 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, bool do_toast, bool for_wraparound,
 	 * Do the actual work --- either FULL or "lazy" vacuum
 	 */
 	if (vacstmt->full)
-		full_vacuum_rel(onerel, vacstmt);
+		heldoff = full_vacuum_rel(onerel, vacstmt);
 	else
-		lazy_vacuum_rel(onerel, vacstmt, vac_strategy, scanned_all);
+		heldoff = lazy_vacuum_rel(onerel, vacstmt, vac_strategy, scanned_all);
 
 	/* Restore userid */
 	SetUserIdAndContext(save_userid, save_secdefcxt);
@@ -1202,6 +1203,10 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, bool do_toast, bool for_wraparound,
 	PopActiveSnapshot();
 	CommitTransactionCommand();
 
+	/* now we can allow interrupts again, if disabled */
+	if (heldoff)
+		RESUME_INTERRUPTS();
+
 	/*
 	 * If the relation has a secondary toast rel, vacuum that too while we
 	 * still hold the session lock on the master table.  Note however that
@@ -1235,8 +1240,11 @@ vacuum_rel(Oid relid, VacuumStmt *vacstmt, bool do_toast, bool for_wraparound,
  *
  *		At entry, we have already established a transaction and opened
  *		and locked the relation.
+ *
+ *		The return value indicates whether this function has held off
+ *		interrupts -- caller must RESUME_INTERRUPTS() after commit if true.
  */
-static void
+static bool
 full_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
 {
 	VacPageListData vacuum_pages;		/* List of pages to vacuum and/or
@@ -1247,6 +1255,7 @@ full_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
 	int			nindexes,
 				i;
 	VRelStats  *vacrelstats;
+	bool		heldoff = false;
 
 	vacuum_set_xid_limits(vacstmt->freeze_min_age, vacstmt->freeze_table_age,
 						  onerel->rd_rel->relisshared,
@@ -1298,7 +1307,7 @@ full_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
 	if (fraged_pages.num_pages > 0)
 	{
 		/* Try to shrink heap */
-		repair_frag(vacrelstats, onerel, &vacuum_pages, &fraged_pages,
+		heldoff = repair_frag(vacrelstats, onerel, &vacuum_pages, &fraged_pages,
 					nindexes, Irel);
 		vac_close_indexes(nindexes, Irel, NoLock);
 	}
@@ -1324,6 +1333,8 @@ full_vacuum_rel(Relation onerel, VacuumStmt *vacstmt)
 	/* report results to the stats collector, too */
 	pgstat_report_vacuum(RelationGetRelid(onerel), onerel->rd_rel->relisshared,
 						 true, vacstmt->analyze, vacrelstats->rel_tuples);
+
+	return heldoff;
 }
 
 
@@ -1874,8 +1885,11 @@ scan_heap(VRelStats *vacrelstats, Relation onerel,
  *		for them after committing (in hack-manner - without losing locks
  *		and freeing memory!) current transaction. It truncates relation
  *		if some end-blocks are gone away.
+ *
+ *		The return value indicates whether this function has held off
+ *		interrupts -- caller must RESUME_INTERRUPTS() after commit if true.
  */
-static void
+static bool
 repair_frag(VRelStats *vacrelstats, Relation onerel,
 			VacPageList vacuum_pages, VacPageList fraged_pages,
 			int nindexes, Relation *Irel)
@@ -1900,6 +1914,7 @@ repair_frag(VRelStats *vacrelstats, Relation onerel,
 	int			keep_tuples = 0;
 	int			keep_indexed_tuples = 0;
 	PGRUsage	ru0;
+	bool		heldoff = false;
 
 	pg_rusage_init(&ru0);
 
@@ -2705,8 +2720,12 @@ repair_frag(VRelStats *vacrelstats, Relation onerel,
 		 *
 		 * XXX This desperately needs to be revisited.	Any failure after this
 		 * point will result in a PANIC "cannot abort transaction nnn, it was
-		 * already committed"!
+		 * already committed"!  As a precaution, we prevent cancel interrupts
+		 * after this point to mitigate this problem; caller is responsible for
+		 * re-enabling them after committing the transaction.
 		 */
+		HOLD_INTERRUPTS();
+		heldoff = true;
 		ForceSyncCommit();
 		(void) RecordTransactionCommit();
 	}
@@ -2906,6 +2925,8 @@ repair_frag(VRelStats *vacrelstats, Relation onerel,
 		pfree(vacrelstats->vtlinks);
 
 	ExecContext_Finish(&ec);
+
+	return heldoff;
 }
 
 /*
diff --git a/src/backend/commands/vacuumlazy.c b/src/backend/commands/vacuumlazy.c
index 8fb06e4a68..92fee334ff 100644
--- a/src/backend/commands/vacuumlazy.c
+++ b/src/backend/commands/vacuumlazy.c
@@ -29,7 +29,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.122 2009/08/24 02:18:32 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/vacuumlazy.c,v 1.123 2009/11/10 18:00:06 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -140,8 +140,11 @@ static int	vac_cmp_itemptr(const void *left, const void *right);
  *
  *		At entry, we have already established a transaction and opened
  *		and locked the relation.
+ *
+ *		The return value indicates whether this function has held off
+ *		interrupts -- caller must RESUME_INTERRUPTS() after commit if true.
  */
-void
+bool
 lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
 				BufferAccessStrategy bstrategy, bool *scanned_all)
 {
@@ -153,6 +156,7 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
 	TimestampTz starttime = 0;
 	bool		scan_all;
 	TransactionId freezeTableLimit;
+	bool		heldoff = false;
 
 	pg_rusage_init(&ru0);
 
@@ -194,12 +198,22 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
 	 *
 	 * Don't even think about it unless we have a shot at releasing a goodly
 	 * number of pages.  Otherwise, the time taken isn't worth it.
+	 *
+	 * Note that after we've truncated the heap, it's too late to abort the
+	 * transaction; doing so would lose the sinval messages needed to tell
+	 * the other backends about the table being shrunk.  We prevent interrupts
+	 * in that case; caller is responsible for re-enabling them after
+	 * committing the transaction.
 	 */
 	possibly_freeable = vacrelstats->rel_pages - vacrelstats->nonempty_pages;
 	if (possibly_freeable > 0 &&
 		(possibly_freeable >= REL_TRUNCATE_MINIMUM ||
 		 possibly_freeable >= vacrelstats->rel_pages / REL_TRUNCATE_FRACTION))
+	{
+		HOLD_INTERRUPTS();
+		heldoff = true;
 		lazy_truncate_heap(onerel, vacrelstats);
+	}
 
 	/* Vacuum the Free Space Map */
 	FreeSpaceMapVacuum(onerel);
@@ -246,6 +260,8 @@ lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
 
 	if (scanned_all)
 		*scanned_all = vacrelstats->scanned_all;
+
+	return heldoff;
 }
 
 
diff --git a/src/include/commands/vacuum.h b/src/include/commands/vacuum.h
index b7dff7b0c4..bd313f3184 100644
--- a/src/include/commands/vacuum.h
+++ b/src/include/commands/vacuum.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/commands/vacuum.h,v 1.85 2009/06/11 14:49:11 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/commands/vacuum.h,v 1.86 2009/11/10 18:00:06 alvherre Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -146,7 +146,7 @@ extern bool vac_is_partial_index(Relation indrel);
 extern void vacuum_delay_point(void);
 
 /* in commands/vacuumlazy.c */
-extern void lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
+extern bool lazy_vacuum_rel(Relation onerel, VacuumStmt *vacstmt,
 				BufferAccessStrategy bstrategy, bool *scanned_all);
 
 /* in commands/analyze.c */