7.0.2 and 6.5.3 performance

After upgrading to 7.0.2, one of my queries ran much slower on 7.0.2:

7.0.2  took 17 minutes  (After 'optimization' by SET ENABLE_SEQSCAN=OFF)

6.5.3 took 2 minutes

The following is the query/explain under 6.5.3:

super=> select version();
version
-------------------------------------------------------------------
PostgreSQL 6.5.3 on i586-pc-linux-gnu, compiled by gcc egcs-2.91.66
(1 row)

explain  select itm_section, itm_brand, itm_itemno, sum(stl_qty)
     from stl, item where stl_itemno = itm_itemno
        and stl_discounttype in ('','S','V')
        and stl_trxdate>='Jul 01, 2000' and stl_trxdate<='Jul 02, 2000'
        and stl_status='N'
        and itm_sectiontype='O'
        and itm_section >='101'
        and itm_section <='135'
        group by itm_section, itm_brand, itm_itemno;
NOTICE:  QUERY PLAN:

Aggregate  (cost=25780.13 rows=55386 width=72)
  ->  Group  (cost=25780.13 rows=55386 width=72)
        ->  Sort  (cost=25780.13 rows=55386 width=72)
              ->  Hash Join  (cost=25780.13 rows=55386 width=72)
                    ->  Index Scan using stl_datetrx on stl
(cost=15488.75
rows=210658 width=36)
                    ->  Hash  (cost=3225.66 rows=2879 width=36)
                          ->  Seq Scan on item  (cost=3225.66 rows=2879
width=36)

Under 7.0.2, there are no Hash Join or Hash

Are there any way to optimize this type of query?  I have SET
ENABLE_SEQSCAN=OFF
and increased the buffer size.  Without SEQSCAN=OFF the query took even
longer than
17 minutes.


Thanks,
Thomas.