Re: determining random_page_cost value - Mailing list pgsql-hackers

On Tue, Oct 25, 2005 at 04:37:34PM -0400, Yohanes Santoso wrote:
> > All of this goes to uphold Tom's general assertion that the default of 4 is 
> > more or less correct 
> 
> Doesn't this show that 4:1 is a pretty optimistic value considering
> that no long-running db files are fragmentation-free?
> 
> >but the calculation in which we're using that number is 
> > not.
> 
> The calculation inside the planner, IOW, how the planner uses the RPC
> value?

The problem with RPC is that the estimator functions are sub-optimal in
many cases and tend to favor seqscan when they shouldn't. This is why
many people run with RPC set unrealistically low, such as 2.

IMHO until the estimator algorithms improve worrying about RPC is
pointless.
-- 
Jim C. Nasby, Sr. Engineering Consultant      jnasby@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461