On 2013-05-23 22:09:02 -0400, Robert Haas wrote: > On Thu, May 23, 2013 at 1:51 PM, Andres Freund <and...@2ndquadrant.com> wrote: > > So, what I propose instead is basically: > > 1) only vacuum non-all-visible pages, even when doing it for > > anti-wraparound > > Check. We might want an option to force a scan of the whole relation.
Yea, thought of that as well. VACUUM (DEEP) ;). > > 3) When we cannot mark a page all-visible or we cannot get the cleanup > > lock, remember the oldest xmin on that page. We could set all visible > > in the former case, but we want the page to be cleaned up sometime > > soonish. > I think you mean "in the latter case" not "in the former case". If > not, then I'm confused. Uh. Yes. > > We don't even necessarily need to log the hint bits for all items since > > the redo for all_visible could make sure all items are hinted. The only > > problem is knowing up to where we can truncate pg_clog... > [all-visible cannot restore hint bits without FPI because of torn pages] I haven't yet thought about this sufficiently yet. I think we might have a chance of working around this, let me ponder a bit. But even if that means needing a full page write via the usual mechanism for all visible if any hint bits needed to be set we are still out far ahead of the current state imo. * cleanup would quite possibly do an FPI shortly after in vacuum anyway. If we do it for all visible, it possibly does not need to be done for it. * freezing would FPI almost guaranteedly since we do it so much later. * Not having to rescan the whole heap will be a bigger cost saving... Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
