Problem with complex query

Hello!

Query:

SELECT DISTINCT p.subsec_id
FROM central cn, shops sh, districts d, positions p
WHERE cn.shop_id = sh.shop_id AND sh.distr_id = d.distr_id
AND d.city_id = %d AND cn.pos_id = p.pos_id
AND cn.date_i >= current_date - '7 days'::timespan

While running postgres slowly eats all swap space (30 Meg) and aborts:

pqReadData() -- backend closed the channel unexpectedly.
This probably means the backend terminated abnormally before or
while processing the request.

Is it I just have not enough memory or bug?

Oleg.
----
Oleg Broytmann http://members.xoom.com/phd2/ phd2(at)earthling(dot)net
Programmers don't die, they just GOSUB without RETURN.