diff --git a/doc/src/sgml/ref/truncate.sgml b/doc/src/sgml/ref/truncate.sgml
index fc65f65db55..aa27890f47e 100644
--- a/doc/src/sgml/ref/truncate.sgml
+++ b/doc/src/sgml/ref/truncate.sgml
@@ -1,5 +1,5 @@
 <!--
-$Header: /cvsroot/pgsql/doc/src/sgml/ref/truncate.sgml,v 1.13 2003/09/12 00:12:47 tgl Exp $
+$Header: /cvsroot/pgsql/doc/src/sgml/ref/truncate.sgml,v 1.14 2003/09/19 21:04:19 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -50,6 +50,16 @@ TRUNCATE [ TABLE ] <replaceable class="PARAMETER">name</replaceable>
   </variablelist>
  </refsect1>
 
+ <refsect1>
+  <title>Notes</title>
+
+  <para>
+   <command>TRUNCATE</> cannot be used if there are foreign-key references
+   to the table from other tables.  Checking validity in such cases would
+   require table scans, and the whole point is not to do one.
+  </para>
+ </refsect1>
+
  <refsect1>
   <title>Examples</title>
 
diff --git a/src/backend/catalog/heap.c b/src/backend/catalog/heap.c
index c3253677f93..ce189ff903b 100644
--- a/src/backend/catalog/heap.c
+++ b/src/backend/catalog/heap.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/catalog/heap.c,v 1.251 2003/08/04 02:39:58 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/catalog/heap.c,v 1.252 2003/09/19 21:04:19 tgl Exp $
  *
  *
  * INTERFACE ROUTINES
@@ -1966,9 +1966,11 @@ RelationTruncateIndexes(Oid heapId)
 /*
  *	 heap_truncate
  *
- *	 This routine is used to truncate the data from the
- *	 storage manager of any data within the relation handed
- *	 to this routine.  This is not transaction-safe!
+ *	 This routine deletes all data within the specified relation.
+ *
+ * This is not transaction-safe!  There is another, transaction-safe
+ * implementation in commands/cluster.c.  We now use this only for
+ * ON COMMIT truncation of temporary tables, where it doesn't matter.
  */
 void
 heap_truncate(Oid rid)
@@ -1979,6 +1981,9 @@ heap_truncate(Oid rid)
 	/* Open relation for processing, and grab exclusive access on it. */
 	rel = heap_open(rid, AccessExclusiveLock);
 
+	/* Don't allow truncate on tables that are referenced by foreign keys */
+	heap_truncate_check_FKs(rel);
+
 	/*
 	 * Release any buffers associated with this relation.  If they're
 	 * dirty, they're just dropped without bothering to flush to disk.
@@ -2003,3 +2008,61 @@ heap_truncate(Oid rid)
 	 */
 	heap_close(rel, NoLock);
 }
+
+/*
+ * heap_truncate_check_FKs
+ *		Check for foreign keys referencing a relation that's to be truncated
+ *
+ * We disallow such FKs (except self-referential ones) since the whole point
+ * of TRUNCATE is to not scan the individual rows to be thrown away.
+ *
+ * This is split out so it can be shared by both implementations of truncate.
+ * Caller should already hold a suitable lock on the relation.
+ */
+void
+heap_truncate_check_FKs(Relation rel)
+{
+	Oid			relid = RelationGetRelid(rel);
+	ScanKeyData key;
+	Relation	fkeyRel;
+	SysScanDesc fkeyScan;
+	HeapTuple	tuple;
+
+	/*
+	 * Fast path: if the relation has no triggers, it surely has no FKs
+	 * either.
+	 */
+	if (rel->rd_rel->reltriggers == 0)
+		return;
+
+	/*
+	 * Otherwise, must scan pg_constraint.  Right now, this is a seqscan
+	 * because there is no available index on confrelid.
+	 */
+	fkeyRel = heap_openr(ConstraintRelationName, AccessShareLock);
+
+	ScanKeyEntryInitialize(&key, 0,
+						   Anum_pg_constraint_confrelid,
+						   F_OIDEQ,
+						   ObjectIdGetDatum(relid));
+
+	fkeyScan = systable_beginscan(fkeyRel, NULL, false,
+								  SnapshotNow, 1, &key);
+
+	while (HeapTupleIsValid(tuple = systable_getnext(fkeyScan)))
+	{
+		Form_pg_constraint con = (Form_pg_constraint) GETSTRUCT(tuple);
+
+		if (con->contype == CONSTRAINT_FOREIGN && con->conrelid != relid)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("cannot truncate a table referenced in a foreign key constraint"),
+					 errdetail("Table \"%s\" references \"%s\" via foreign key constraint \"%s\".",
+							   get_rel_name(con->conrelid),
+							   RelationGetRelationName(rel),
+							   NameStr(con->conname))));
+	}
+
+	systable_endscan(fkeyScan);
+	heap_close(fkeyRel, AccessShareLock);
+}
diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index b99d68b3400..fc8a87123fe 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 1.81 2003/09/15 00:26:31 petere Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/tablecmds.c,v 1.82 2003/09/19 21:04:20 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -365,15 +365,9 @@ void
 TruncateRelation(const RangeVar *relation)
 {
 	Relation	rel;
-	Oid			relid;
-	ScanKeyData key;
-	Relation	fkeyRel;
-	SysScanDesc fkeyScan;
-	HeapTuple	tuple;
 
 	/* Grab exclusive lock in preparation for truncate */
 	rel = heap_openrv(relation, AccessExclusiveLock);
-	relid = RelationGetRelid(rel);
 
 	/* Only allow truncate on regular tables */
 	if (rel->rd_rel->relkind != RELKIND_RELATION)
@@ -383,7 +377,7 @@ TruncateRelation(const RangeVar *relation)
 						RelationGetRelationName(rel))));
 
 	/* Permissions checks */
-	if (!pg_class_ownercheck(relid, GetUserId()))
+	if (!pg_class_ownercheck(RelationGetRelid(rel), GetUserId()))
 		aclcheck_error(ACLCHECK_NOT_OWNER, ACL_KIND_CLASS,
 					   RelationGetRelationName(rel));
 
@@ -405,35 +399,7 @@ TruncateRelation(const RangeVar *relation)
 	/*
 	 * Don't allow truncate on tables which are referenced by foreign keys
 	 */
-	fkeyRel = heap_openr(ConstraintRelationName, AccessShareLock);
-
-	ScanKeyEntryInitialize(&key, 0,
-						   Anum_pg_constraint_confrelid,
-						   F_OIDEQ,
-						   ObjectIdGetDatum(relid));
-
-	fkeyScan = systable_beginscan(fkeyRel, 0, false,
-								  SnapshotNow, 1, &key);
-
-	/*
-	 * First foreign key found with us as the reference should throw an
-	 * error.
-	 */
-	while (HeapTupleIsValid(tuple = systable_getnext(fkeyScan)))
-	{
-		Form_pg_constraint con = (Form_pg_constraint) GETSTRUCT(tuple);
-
-		if (con->contype == 'f' && con->conrelid != relid)
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-					 errmsg("cannot truncate a table referenced in a foreign key constraint"),
-					 errdetail("Table \"%s\" references this one via foreign key constraint \"%s\".",
-							   get_rel_name(con->conrelid),
-							   NameStr(con->conname))));
-	}
-
-	systable_endscan(fkeyScan);
-	heap_close(fkeyRel, AccessShareLock);
+	heap_truncate_check_FKs(rel);
 
 	/*
 	 * Do the real work using the same technique as cluster, but without
@@ -3137,11 +3103,28 @@ AlterTableAddForeignKeyConstraint(Relation rel, FkConstraint *fkconstraint)
 		aclcheck_error(aclresult, ACL_KIND_CLASS,
 					   RelationGetRelationName(rel));
 
-	if (isTempNamespace(RelationGetNamespace(pkrel)) &&
-		!isTempNamespace(RelationGetNamespace(rel)))
-		ereport(ERROR,
-				(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
-				 errmsg("cannot reference temporary table from permanent table constraint")));
+	/*
+	 * Disallow reference from permanent table to temp table or vice versa.
+	 * (The ban on perm->temp is for fairly obvious reasons.  The ban on
+	 * temp->perm is because other backends might need to run the RI triggers
+	 * on the perm table, but they can't reliably see tuples the owning
+	 * backend has created in the temp table, because non-shared buffers
+	 * are used for temp tables.)
+	 */
+	if (isTempNamespace(RelationGetNamespace(pkrel)))
+	{
+		if (!isTempNamespace(RelationGetNamespace(rel)))
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					 errmsg("cannot reference temporary table from permanent table constraint")));
+	}
+	else
+	{
+		if (isTempNamespace(RelationGetNamespace(rel)))
+			ereport(ERROR,
+					(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+					 errmsg("cannot reference permanent table from temporary table constraint")));
+	}
 
 	/*
 	 * Look up the referencing attributes to make sure they exist, and
diff --git a/src/include/catalog/heap.h b/src/include/catalog/heap.h
index 86c97ff4786..a9cd65ff068 100644
--- a/src/include/catalog/heap.h
+++ b/src/include/catalog/heap.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: heap.h,v 1.61 2003/08/04 02:40:10 momjian Exp $
+ * $Id: heap.h,v 1.62 2003/09/19 21:04:20 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -48,6 +48,8 @@ extern void heap_drop_with_catalog(Oid rid);
 
 extern void heap_truncate(Oid rid);
 
+extern void heap_truncate_check_FKs(Relation rel);
+
 extern void AddRelationRawConstraints(Relation rel,
 						  List *rawColDefaults,
 						  List *rawConstraints);
diff --git a/src/test/regress/expected/truncate.out b/src/test/regress/expected/truncate.out
index 91ea40b7929..2cd41f83ba0 100644
--- a/src/test/regress/expected/truncate.out
+++ b/src/test/regress/expected/truncate.out
@@ -42,7 +42,7 @@ SELECT * FROM truncate_a;
 
 TRUNCATE truncate_a;
 ERROR:  cannot truncate a table referenced in a foreign key constraint
-DETAIL:  Table "truncate_b" references this one via foreign key constraint "$1".
+DETAIL:  Table "truncate_b" references "truncate_a" via foreign key constraint "$1".
 SELECT * FROM truncate_a;
  col1 
 ------