Get rid of rd_nblocks field in relcache entries. Turns out this was

costing us lots more to maintain than it was worth.  On shared tables
it was of exactly zero benefit because we couldn't trust it to be
up to date.  On temp tables it sometimes saved an lseek, but not often
enough to be worth getting excited about.  And the real problem was that
we forced an lseek on every relcache flush in order to update the field.
So all in all it seems best to lose the complexity.

src/include/access/relscan.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/relscan.h,v 1.34 2003/11/29 22:40:55 pgsql Exp $
+ * $PostgreSQL: pgsql/src/include/access/relscan.h,v 1.35 2004/05/08 19:09:25 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -25,6 +25,7 @@ typedef struct HeapScanDescData
 	Snapshot	rs_snapshot;	/* snapshot to see */
 	int			rs_nkeys;		/* number of scan keys */
 	ScanKey		rs_key;			/* array of scan key descriptors */
+	BlockNumber rs_nblocks;		/* number of blocks to scan */
 
 	/* scan current state */
 	HeapTupleData rs_ctup;		/* current tuple in scan, if any */