diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index 3d782d2e5f4..041fdfb70bd 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/catalog/index.c,v 1.219.2.3 2008/01/03 21:25:33 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/catalog/index.c,v 1.219.2.4 2008/05/27 21:14:00 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -33,11 +33,13 @@
 #include "catalog/heap.h"
 #include "catalog/index.h"
 #include "catalog/indexing.h"
+#include "catalog/namespace.h"
 #include "catalog/pg_constraint.h"
 #include "catalog/pg_index.h"
 #include "catalog/pg_opclass.h"
 #include "catalog/pg_proc.h"
 #include "catalog/pg_type.h"
+#include "commands/tablecmds.h"
 #include "executor/executor.h"
 #include "miscadmin.h"
 #include "optimizer/clauses.h"
@@ -1684,6 +1686,21 @@ reindex_index(Oid indexId)
 	/* Open and lock the parent heap relation */
 	heapRelation = heap_open(heapId, AccessExclusiveLock);
 
+	/*
+	 * Don't allow reindex on temp tables of other backends ... their local
+	 * buffer manager is not going to cope.
+	 */
+	if (isOtherTempNamespace(RelationGetNamespace(iRel)))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("cannot reindex temporary tables of other sessions")));
+
+	/*
+	 * Also check for active uses of the index in the current transaction;
+	 * we don't want to reindex underneath an open indexscan.
+	 */
+	CheckTableNotInUse(iRel, "REINDEX INDEX");
+
 	SetReindexProcessing(heapId, indexId);
 
 	/*
diff --git a/src/backend/commands/cluster.c b/src/backend/commands/cluster.c
index 3256b172206..19ea0cac1ae 100644
--- a/src/backend/commands/cluster.c
+++ b/src/backend/commands/cluster.c
@@ -11,7 +11,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/cluster.c,v 1.116.2.3 2007/09/12 15:16:24 alvherre Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/cluster.c,v 1.116.2.4 2008/05/27 21:14:00 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -398,6 +398,12 @@ cluster_rel(RelToCluster *rvtc, bool recheck)
 				 errmsg("\"%s\" is a system catalog",
 						RelationGetRelationName(OldHeap))));
 
+	/*
+	 * Also check for active uses of the relation in the current transaction,
+	 * including open scans and pending AFTER trigger events.
+	 */
+	CheckTableNotInUse(OldHeap, "CLUSTER");
+
 	/* Drop relcache refcnt on OldIndex, but keep lock */
 	index_close(OldIndex);
 
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 97caafbb8e1..ccc25c88f4a 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/tablecmds.c,v 1.91.2.3 2008/05/09 22:38:05 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/tablecmds.c,v 1.91.2.4 2008/05/27 21:14:00 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -397,6 +397,12 @@ TruncateRelation(const RangeVar *relation)
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 			  errmsg("cannot truncate temporary tables of other sessions")));
 
+	/*
+	 * Also check for active uses of the relation in the current
+	 * transaction, including open scans and pending AFTER trigger events.
+	 */
+	CheckTableNotInUse(rel, "TRUNCATE");
+
 	/*
 	 * Don't allow truncate on tables which are referenced by foreign keys
 	 */
@@ -1592,6 +1598,48 @@ update_ri_trigger_args(Oid relid,
 	CommandCounterIncrement();
 }
 
+/*
+ * Disallow TRUNCATE (and similar commands) when the current backend has
+ * any open reference to the target table besides the one just acquired by
+ * the calling command; this implies there's an open cursor or active plan.
+ * We need this check because our AccessExclusiveLock doesn't protect us
+ * against stomping on our own foot, only other people's feet!
+ *
+ * We also reject these commands if there are any pending AFTER trigger events
+ * for the rel.  This is certainly necessary for CLUSTER, because it does not
+ * preserve tuple TIDs and so the pending events would try to fetch the wrong
+ * tuples.  It might be overly cautious in other cases, but again it seems
+ * better to err on the side of paranoia.
+ *
+ * REINDEX calls this with "rel" referencing the index to be rebuilt; here
+ * we are worried about active indexscans on the index.  The trigger-event
+ * check can be skipped, since we are doing no damage to the parent table.
+ *
+ * The statement name (eg, "TRUNCATE") is passed for use in error messages.
+ */
+void
+CheckTableNotInUse(Relation rel, const char *stmt)
+{
+	int			expected_refcnt;
+
+	expected_refcnt = rel->rd_isnailed ? 2 : 1;
+	if (rel->rd_refcnt != expected_refcnt)
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_IN_USE),
+				 /* translator: first %s is a SQL command, eg ALTER TABLE */
+				 errmsg("cannot %s \"%s\" because "
+						"it is being used by active queries in this session",
+						stmt, RelationGetRelationName(rel))));
+
+	if (rel->rd_rel->relkind != RELKIND_INDEX &&
+		AfterTriggerPendingOnRel(RelationGetRelid(rel)))
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_IN_USE),
+				 /* translator: first %s is a SQL command, eg ALTER TABLE */
+				 errmsg("cannot %s \"%s\" because "
+						"it has pending trigger events",
+						stmt, RelationGetRelationName(rel))));
+}
 
 /* ----------------
  *		AlterTableAddColumn
diff --git a/src/backend/commands/trigger.c b/src/backend/commands/trigger.c
index 4b9d5efea98..9d2b2b64e98 100644
--- a/src/backend/commands/trigger.c
+++ b/src/backend/commands/trigger.c
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/trigger.c,v 1.159.2.2 2006/01/12 21:49:31 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/trigger.c,v 1.159.2.3 2008/05/27 21:14:00 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -2365,6 +2365,49 @@ DeferredTriggerSetState(ConstraintsSetStmt *stmt)
 	deferredTriggers->deftrig_events_imm = NULL;
 }
 
+/* ----------
+ * AfterTriggerPendingOnRel()
+ *		Test to see if there are any pending after-trigger events for rel.
+ *
+ * This is used by TRUNCATE, CLUSTER, ALTER TABLE, etc to detect whether
+ * it is unsafe to perform major surgery on a relation.  Note that only
+ * local pending events are examined.  We assume that having exclusive lock
+ * on a rel guarantees there are no unserviced events in other backends ---
+ * but having a lock does not prevent there being such events in our own.
+ *
+ * In some scenarios it'd be reasonable to remove pending events (more
+ * specifically, mark them DONE by the current subxact) but without a lot
+ * of knowledge of the trigger semantics we can't do this in general.
+ * ----------
+ */
+bool
+AfterTriggerPendingOnRel(Oid relid)
+{
+	DeferredTriggerEvent event;
+
+	/* No-op if we aren't in a transaction.  (Shouldn't happen?) */
+	if (deferredTriggers == NULL)
+		return false;
+
+	/* Scan queued events */
+	for (event = deferredTriggers->deftrig_events;
+		 event != NULL;
+		 event = event->dte_next)
+	{
+		/*
+		 * We can ignore completed events.
+		 */
+		if (event->dte_event & (TRIGGER_DEFERRED_DONE |
+								TRIGGER_DEFERRED_CANCELED))
+			continue;
+
+		if (event->dte_relid == relid)
+			return true;
+	}
+
+	return false;
+}
+
 
 /* ----------
  * DeferredTriggerSaveEvent()
diff --git a/src/include/commands/tablecmds.h b/src/include/commands/tablecmds.h
index 793f3a6c799..4fb15de071c 100644
--- a/src/include/commands/tablecmds.h
+++ b/src/include/commands/tablecmds.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: tablecmds.h,v 1.13 2003/08/04 02:40:13 momjian Exp $
+ * $Id: tablecmds.h,v 1.13.4.1 2008/05/27 21:14:00 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -15,6 +15,7 @@
 #define TABLECMDS_H
 
 #include "nodes/parsenodes.h"
+#include "utils/rel.h"
 
 extern void AlterTableAddColumn(Oid myrelid, bool recurse, ColumnDef *colDef);
 
@@ -55,6 +56,8 @@ extern Oid	DefineRelation(CreateStmt *stmt, char relkind);
 
 extern void RemoveRelation(const RangeVar *relation, DropBehavior behavior);
 
+extern void CheckTableNotInUse(Relation rel, const char *stmt);
+
 extern void TruncateRelation(const RangeVar *relation);
 
 extern void renameatt(Oid myrelid,
diff --git a/src/include/commands/trigger.h b/src/include/commands/trigger.h
index fe8f6af61d9..9a15bbdf04a 100644
--- a/src/include/commands/trigger.h
+++ b/src/include/commands/trigger.h
@@ -6,7 +6,7 @@
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $Id: trigger.h,v 1.44 2003/10/06 16:38:28 tgl Exp $
+ * $Id: trigger.h,v 1.44.2.1 2008/05/27 21:14:00 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -192,6 +192,8 @@ extern void DeferredTriggerAbortXact(void);
 
 extern void DeferredTriggerSetState(ConstraintsSetStmt *stmt);
 
+extern bool AfterTriggerPendingOnRel(Oid relid);
+
 
 /*
  * in utils/adt/ri_triggers.c