Alvaro Herrera wrote: > Excerpts from Robert Haas's message of mi?? jun 02 14:16:33 -0400 2010: > > > We could, but I think we'd be better off just freezing at the time we > > mark the page PD_ALL_VISIBLE and then using the visibility map for > > both purposes. Keeping around the old xmin values after every tuple > > on the page is visible to every running transaction is useful only for > > forensics, and building a whole new freeze map just to retain that > > information longer (and eventually force a massive anti-wraparound > > vacuum) seems like overkill. > > Reducing the xid wraparound horizon "a bit" is reasonable, but moving it > all the way forward to OldestXmin is a bit much, methinks. > > Besides, there's another argument for not freezing tuples immediately: > they may be updated shortly thereafter, causing extra churn for no gain. > > I'd prefer a setting that would tell the system to freeze all tuples > that fall within a safety range whenever any tuple in the page is frozen > -- weren't you working on a patch to do this? (was it Jeff Davis?) > > (BTW maybe instead of separate visibility and freeze maps we could have > two bits in the visibility map?)
Yeah, the two-bits idea was suggested during the conversation core had about the issue. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + None of us is going to be here forever. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
