Re: count(*) performance

On Mon, Mar 27, 2006 at 03:34:32PM +0200, G?briel ?kos wrote:
> Hi,
>
> I guess this is an age-old 100times answered question, but I didn't find
> the answer to it yet (neither in the FAQ nor in the mailing list archives).
>
> Question: I have a table with 2.5M rows. count(*) on this table is
> running 4 minutes long. (dual opteron, 4gig ram, db on 4 disk raid10
> array (sata, not scsi)) Is this normal? How could I make it run faster?
> Maybe make it run faster for the 2nd time? Which parameters should I
> change in postgresql.conf and how?

First, count(*) on PostgreSQL tends to be slow because you can't do
index covering[1].

But in this case, I'd bet money that if it's taking 4 minutes something
else is wrong. Have you been vacuuming that table frequently enough?
What's SELECT relpages FROM pg_class WHERE relname='tablename' show?

[1] http://www.pervasive-postgres.com/lp/newsletters/2006/Insights_postgres_Feb.asp#5
--
Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461