On Tue, Jun 16, 2009 at 11:16 AM, Alexander Staubo<alex@xxxxxxxxxx> wrote: > On Tue, Jun 16, 2009 at 4:36 PM, Tom Lane<tgl@xxxxxxxxxxxxx> wrote: >> Actually the easiest way to fix that is to get rid of the LIMIT. >> (Maybe use a cursor instead, and fetch only twenty rows.) LIMIT >> magnifies the risks from any estimation error, and you've got a lot >> of that here ... > > There's no cursor support in ActiveRecord, the ORM library we use, and > I'm not going to write it. Anyway, I would prefer not to gloss over > the underlying problem with something that requires a "TODO" next to > it. What can be done to fix the underlying problem? Nothing? Basically, we need a system that can accurately estimate multi-column selectivity, or else some kind of planner hints. http://archives.postgresql.org/pgsql-performance/2009-06/msg00023.php http://archives.postgresql.org/pgsql-performance/2009-06/msg00119.php (with apologies for linking to my own posts, but you can go back and read the whole thread if you're interested) ...Robert -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
