Re: Strange Index behavior

=?iso-8859-2?Q?Egy=FCd_Csaba_=28Freemail=29?= <csegyud@freemail.hu> writes:
> The difference between the result times is 16x. I can't understand why the
> planner thinks it is the better way...

The planner thinks that because it thinks the second query will fetch
1500 times as many rows as the first.  Now that I look more carefully
I see that both of those row estimates are off, the first by a lot.
Have you ANALYZEd this table lately?  If you have, it might be a good
idea to increase the statistics target for the tstamp column.

You might also need to play around with random_page_cost, but it will be
counterproductive to touch that until the rowcount estimates are in the
vicinity of reality.

            regards, tom lane