Re: BUG #5722: vacuum full does not update last_vacuum statistics

On Mon, Oct 25, 2010 at 11:03:07AM -0400, Tom Lane wrote:
> Perhaps. The new implementation of VACUUM FULL is really more like a
> CLUSTER, or one of the rewriting variants of ALTER TABLE. Should all
> of those operations result in an update of last_vacuum? From an
> implementation standpoint it's difficult to say that only some of them
> should, because all of them result in a table that has no immediate
> need for vacuuming. The only argument I can see for having only VACUUM
> FULL update the timestamp is that it's called VACUUM and the others
> aren't. Which is an argument, but not a terribly impressive one IMO.

I agree it's an unimpressive argument; perhaps it's worth considering that
last_vacuum doesn't really indicate how much a particular table needs
vacuuming, either. Without the update/delete statistics telling you how much
updating and deleting has happened since the last vacuum, there's really no
way of guessing how vacuum-needy something might be based only on available
statistics. last_vacuum is just a nice way of verifying that [auto]vacuum
happens on the table sometimes, and influencing an administrator's WAGs about
what needs vacuuming.

--
Joshua Tolley / eggyknap
End Point Corporation
http://www.endpoint.com