TPC-R benchmarks

I am running TPC-R benchmarks with a scale factor of 1, which correspond
to approximately 1 GB database size on PostgreSQL 7.3.4 installed on
CygWin on Windows XP. I dedicated 128 MB of shared memory to my postrges
installation.
Most of the queries were able to complete in a matter of minutes, but
query 17 was taking hours and hours. The query is show below. Is there
any way to optimize it ?

select
sum(l_extendedprice) / 7.0 as avg_yearly
from
lineitem,
part
where
p_partkey = l_partkey
and p_brand = 'Brand#11'
and p_container = 'SM PKG'
and l_quantity < (
select
0.2 * avg(l_quantity)
from
lineitem
where
l_partkey = p_partkey
);

Thanks.

Oleg

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