This is actually more of a fundamental problem with mdtruncate. It

looks
like someone just didn't add support for multiple segments for
truncation.

The following patch seems to do the right thing, for me at least.
It passed my tests, my data looks right(no data that shouldn't be in
there) and regression is ok.

Ole Gjerde

src/backend/storage/smgr/md.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/smgr/md.c,v 1.42 1999/04/05 22:25:11 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/smgr/md.c,v 1.43 1999/05/17 06:38:41 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -711,15 +711,26 @@ mdtruncate(Relation reln, int nblocks)
 	MdfdVec    *v;
 
 #ifndef LET_OS_MANAGE_FILESIZE
-	int			curnblk;
+	int			curnblk,
+					i,
+					oldsegno,
+					newsegno;
+	char		fname[NAMEDATALEN];
+	char		tname[NAMEDATALEN + 10];
 
 	curnblk = mdnblocks(reln);
-	if (curnblk / RELSEG_SIZE > 0)
-	{
-		elog(NOTICE, "Can't truncate multi-segments relation %s",
-			 reln->rd_rel->relname.data);
-		return curnblk;
-	}
+	oldsegno = curnblk / RELSEG_SIZE;
+	newsegno = nblocks / RELSEG_SIZE;
+
+	StrNCpy(fname, RelationGetRelationName(reln)->data, NAMEDATALEN);
+
+	if (newsegno < oldsegno) {
+		for (i = (newsegno + 1);; i++) {
+			sprintf(tname, "%s.%d", fname, i);
+			if (FileNameUnlink(tname) < 0)
+				break;
+		}
+        }
 #endif
 
 	fd = RelationGetFile(reln);