On Wed, Dec 1, 2010 at 11:40 AM, Heikki Linnakangas <heikki.linnakan...@enterprisedb.com> wrote: > On 01.12.2010 18:25, Robert Haas wrote: >> >> I think we can improve this a bit further by also introducing a >> HEAP_XMIN_FROZEN bit that we set in lieu of overwriting XMIN with >> FrozenXID. This allows us to freeze tuples aggressively - if we want >> - without losing any forensic information. We can then modify the >> above algorithm slightly, so that when we observe that a page is all >> visible, we not only set PD_ALL_VISIBLE on the page but also >> HEAP_XMIN_FROZEN on each tuple. > > Hmm, actually, if we're willing to believe PD_ALL_VISIBLE in the page header > over the xmin/xmax on the tuples, we could simply not bother doing > anti-wraparound vacuums for pages that have the flag set. I'm not sure what > changes that would require outside heapam.c, as we'd have to be careful to > not trust the xmin/xmax if the flag was set. > > The first update on the page that clears the flag would need to freeze all > the tuples in that scheme.
That seems more complex for no particular gain. I guess it saves an infomask bit, but I'm willing to burn one to reduce code complexity. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers