Re: Setting max_fsm_pages

On Sun, Nov 06, 2005 at 08:05:29PM -0500, Carlos Oliva wrote:
> Thank you for your response Tom.
>
> Should I set the max_fsm_pages to the "total pages needed" obtained from a
> full vacuum or from a analize vacuum? When I run a vacuum analyze (vacuumdb
> -z -v), I get a smaller number of pages needed than when I run a full vacuum
> with analyze (vacuumdb -f -z -v)

There shouldn't be any difference because of analyze. But remember that
as the tables change in size (as well as in the number of dead tuples),
total pages needed can change. For example, if you run a vacuum
immediately after a vacuum full on a system with no other activity,
you'll get:

INFO: free space map: 0 relations, 0 pages stored; 0 total pages needed

That's because there's no dead space to be reclaimed.

Your best bet is to do a vacuum verbose (vacuumdb -v) after the database
has been running for a while using whatever vacuuming scheme you're
going to use (such as pg_autovacuum). That will give you a pretty good
estimate of how many pages you really need. Even that's not 100%
reliable though, so you still need to include extra space as a safety
margin.
--
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