Re: Idea for getting rid of VACUUM FREEZE on cold pages

On 5/26/10 6:32 PM, Robert Haas wrote:
> Hmm, yeah.  Maybe we should freeze when we set PD_ALL_VISIBLE; that
> might be just as good, and simpler.  Assuming the visibility map is
> sufficiently crash-safe/non-buggy, we could then teach VACUUM that
> it's OK to advance relfrozenxid even when doing just a partial vacuum
> - because any pages that were skipped must contain only frozen tuples.
>  Previously you've objected to proposals in this direction because
> they might destroy forensic information, but maybe we should do it
> anyway.

It would be an improvement, and easier than the various ways of never
having to visit the pages, which are all fairly intensive.  Given the
destruction of rollback information, though, we'd probably want a way to
switch this behaviour on and off as an autovacuum setting.

Does this send us down the wrong path, though?  I thought we wanted to
think about removing hint bits so that we could implement things like
CRCs.  No?

--                                  -- Josh Berkus                                    PostgreSQL Experts Inc.
                        http://www.pgexperts.com