Re: [HACKERS] Re: pgsql: Fix free space map to correctly track the total amount of FSM

Dropping -committers.

On Oct 2, 2007, at 10:37 AM, Tatsuo Ishii wrote:
>> Tatsuo Ishii <ishii@postgresql.org> writes:
>>> Sorry for replying to very old message. But... it seems this was not
>>> backported to 8.1 or earlier.
>>
>> Since it involved a change in the FSM API, it didn't seem reasonable
>> to back-patch it.
>
> So for those versions of PostgreSQL the only way to know the
> appropriate FSM pages is change FSM-restart postmaster-do vacuum cycle
> until vacuum reports the same number of "total page needed"?

That's the only easy way I know of, but there is something that might
make life easier if you're using autovacuum... take SELECT sum
(relpages) FROM pg_class and multiply that by
autovacuum_vacuum_scale_factor. If autovac is doing a reasonable job
of keeping up, that should be a maximum of what you'd need in the FSM.

Hrm... what about adding output to vacuum verbose that indicates how
many pages in a relation have free space? That would allow something
like pgfouine to see how many FSM pages were needed. It would also
make it easier to identify relations that could stand a vacuum full/
reindex/cluster (though you'd also want to know something like
average free space per page).
--
Decibel!, aka Jim C. Nasby, Database Architect  decibel@decibel.org
Give your computer some brain candy! www.distributed.net Team #1828