Re: pg_autovacuum and VACUUM FREEZE

On Thu, 2003-10-16 at 10:16, Rod Taylor wrote:
> > The vacuum man page says, "FREEZE is not recommnded for routine use". 
> > That was enough to keep me away.  However if vacuum freeze was
> > considerably lighter than normal database wide vacuums then there might
> > be an advantage to using it.  Especially since when pg_autovaccum
> > decides it's time to deal with xid wraparound, it does it to all the
> > databases, which could a several hours of vacuum on large clusters. 
> 
> Each database has it's own last xid. Just because one database is about
> to go over the limit doesn't mean they all are.  Why don't you treat
> each database independently in this regard (then they wouldn't
> necessarily all be kicked off at once).

My choice of words above was poor, let me try again.

pg_autovacuum does treat each database independently, however assuming
that you never manually run vacuum (which is the eventual goal of
pg_autovacuum), then database wide vacuums will have never been run on
any table in any database, so all databases will approach xid wraparound
at the same time.

So, pg_autovacuum does deal with them separately, but doesn't make an
effort to spread out the vacuums if all / multiple databases happen to
need it at the same time.

In practice, I don't see this as a big problem right now, but it should
still be handled better by pg_autovacuum.