Re: help needed -- sequential scan problem

sarlav kumar <sarlavk(at)yahoo(dot)com> writes:
> I have a query which does not use index scan unless I force postgres to use index scan. I dont want to force postgres, unless there is no way of optimizing this query.

The major issue seems to be in the sub-selects:

> -> Seq Scan on merchant_purchase mp (cost=0.00..95.39 rows=44 width=4) (actual time=2.37..2.58 rows=6 loops=619)
> Filter: (merchant_id = $0)

where the estimated row count is a factor of 7 too high. If the
estimated row count were even a little lower, it'd probably have gone
for an indexscan. You might get some results from increasing the
statistics target for merchant_purchase.merchant_id. If that doesn't
help, I'd think about reducing random_page_cost a little bit.

regards, tom lane