Performance Question Followup

Another small point:

Even after I do:

set enable_seqscan = off;

explain delete from masterfti where masterfti.id = master.id and
master.retrieved < '31-Oct-2001';
NOTICE:  QUERY PLAN:

Nested Loop  (cost=100000000.00..100000511.92 rows=163 width=14)
  ->  Seq Scan on masterfti  (cost=100000000.00..100000000.00 rows=1 width=10)
  ->  Index Scan using master_pkey on master  (cost=0.00..509.89 rows=163
width=4)

EXPLAIN

The full index (both fields) exists on MasterFTI. Why is a delete doing a
dequential scan on it, even after it has been told not to?

However, just after doing a vacuum analyze:

set enable_seqscan = on;
SET VARIABLE
testdb=> explain delete from masterfti where masterfti.id = master.id and
master.retrieved < '31-Oct-2001';
NOTICE:  QUERY PLAN:

Hash Join  (cost=2472.52..94079.09 rows=96051 width=14)
  ->  Seq Scan on masterfti  (cost=0.00..26610.10 rows=1624010 width=10)
  ->  Hash  (cost=2465.31..2465.31 rows=2886 width=4)
        ->  Index Scan using master_retrieved_index on master
(cost=0.00..2465.31 rows=2886 width=4)

EXPLAIN

set enable_seqscan = on doesn't make any difference.

Can someone explain to me what is happening?

I'm running PostgreSQL 7.1.3 on a RH 7.0 based system.

Thanks.

Gordan