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.
-- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
