---------- Forwarded message ----------
From:
Greg Smith <
gsmith@gregsmith.com>
Date: Tue, Mar 11, 2008 at 4:31 AM
Subject: Re: [PERFORM] count * performance issue
To: Joe Mirabal <
jmmirabal@gmail.com>
Cc:
pgsql-performance@postgresql.orgOn 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.
