Hi, I have been reading this conversation for a few days now and I just wanted to ask this. From the release notes, one of the new additions in 8.3 is (Allow col IS NULL to use an index (Teodor)).
Sorry, if I am missing something here, but shouldn't something like this allow us to get a (fast) accurate count ? SELECT COUNT(*) from table WHERE indexed_field IS NULL + SELECT COUNT(*) from table WHERE indexed_field IS NOT NULL *Robins Tharakan* ---------- Forwarded message ---------- From: Greg Smith <[EMAIL PROTECTED]> Date: Tue, Mar 11, 2008 at 4:31 AM Subject: Re: [PERFORM] count * performance issue To: Joe Mirabal <[EMAIL PROTECTED]> Cc: pgsql-performance@postgresql.org On Mon, 10 Mar 2008, Joe Mirabal wrote: > I run queries on the data nad get immediate max and min as well as other > aggrgate functions very quickly, however a select count(*) of the table > takes forever usually nearly an hour or more. Are you sure the form of "select count(*)" you're using is actually utilizing the index to find a useful subset? What do you get out of EXPLAIN ANALZYE on the query? In order for indexes to be helpful a couple of things need to happen: 1) They have to be structured correctly to be useful 2) There needs to be large enough settings for shared_buffes and effective_cache_size that the database things it can use them efficiently 3) The tables involved need to be ANALYZEd to keep their statistics up to date. The parameters to run a 400GB *table* are very different from the defaults; if you want tuning suggestions you should post the non-default entries in your postgresql.conf file from what you've already adjusted along with basic information about your server (PostgreSQL version, OS, memory, disk setup). > We in our warehouse use the count(*) as our verification of counts by > day/month's etc If you've got a database that size and you're doing that sort of thing on it, you really should be considering partitioning as well. -- * Greg Smith [EMAIL PROTECTED] http://www.gregsmith.com Baltimore, MD -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
