Oleg Bartunov <o...@sai.msu.su> writes: > what if you create index (price,title) ?
I think that SELECT ... WHERE ... ORDER BY ... LIMIT is basically an intractable problem. We've recognized the difficulty in connection with btree indexes for a long time, and there is no reason at all to think that KNNGist will somehow magically dodge it. You can either visit *all* of the rows satisfying WHERE (and then sort them), or you can visit the rows in ORDER BY order and hope that you find enough of them satisfying the WHERE in a reasonable amount of time. Either of these strategies loses badly in many real-world cases. Maybe with some sort of fuzzy notion of ordering it'd be possible to go faster, but as long as you insist on an exact ORDER BY result, I don't see any way out of it. One way to be fuzzy is to introduce a maximum search distance: SELECT ... WHERE x < limit AND other-conditions ORDER BY x LIMIT n which essentially works by limiting the damage in the visit-all-the-rows approach. Hans didn't do that in his example, but I wonder how much it'd help (and whether the existing GIST support is adequate for it). regards, tom lane -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers