Tom Lane <tgl@sss.pgh.pa.us> writes:
> Zlatko Calusic <zlatko@iskon.hr> writes:
> > It is now NOT using the index, and I don't understand why? Queries are
> > practically the same, tables are practically the same, why is postgres
> > using indexes in the first case and not in the second?
>
> Because it has substantially different ideas about the sizes of the
> two tables --- notice the different estimated row counts. If you
> haven't "vacuum analyzed" these tables recently, do so to bring the
> planner's statistics up-to-date, and then see what you get. You may
> also care to read the user's manual chapter about EXPLAIN,
> http://www.postgresql.org/users-lounge/docs/7.0/postgres/c4888.htm
>
Yes, thanks to all who helped. 'vacuum analyze' was the magical
incantation that helped.
I still have one uncertainty. Is it possible that after some time
postgres once again decides not to use indices (assuming I haven't run
'vacuum analyze' again)?
--
Zlatko
