Re: Autovacuum in the backend

On K, 2005-06-15 at 13:41 +0800, Qingqing Zhou wrote:
> "Neil Conway" <neilc(at)samurai(dot)com> writes
> >
> > Wasn't the plan to rewrite pg_autovacuum to use the FSM rather than the
> > stats collector?
> >
>
> I don't understand. Currently the basic logic of pg_autovacuum is to use the
> pg_stat_all_tables numbers like n_tup_upd, n_tup_del to determine if a
> relation need to be vacuumed. How to use FSM to get these information?

One can't probably use FSM as it is, as FSM is filled in by vacuum and
this creates a circular dependency.

But it would be very nice to have something _similar_ to FSM, say DSM
(dead space map), which is filled in when a tuple is marked as "dead for
all running backends", which could be used to implement a vacuum which
vacuums only those pages, which do actually contain removable tuples.

--
Hannu Krosing <hannu(at)skype(dot)net>