Clustered/covering indexes (or lack thereof :-)

[adrobj]

This is probably a FAQ, but I can't find a good answer...

So - are there common techniques to compensate for the lack of clustered/covering indexes in PostgreSQL? To be more specific - here is my table (simplified):

topic_id int
post_id int
post_text varchar(1024)

The most used query is: SELECT post_id, post_text FROM Posts WHERE topic_id=XXX. Normally I would have created a clustered index on topic_id, and the whole query would take ~1 disk seek.

What would be the common way to handle this in PostgreSQL, provided that I can't afford 1 disk seek per record returned?