On 16 December 2012 14:41, Andres Freund <and...@2ndquadrant.com> wrote: > On 2012-12-16 13:23:56 +0530, Pavan Deolasee wrote: >> Another idea could have been to NOT clear the visibility bit when a >> HOT update happens. Such tuple can get pruned by HOT prune, so we >> don't need vacuum per se, and the index-only scans are not affected >> because the update was a HOT update, so the index keys did not change >> either. So index-only scans would continue to return the same result. >> Don't know if this would work with hot standby, probably not. > > For IOSs that sounds like an interesting and itself easy to implement > idea, you basically only would need to add a single !use_hot_update in > the if blocks doing the PageClearAllVisible in heap_update. > This probably could make IOSs far more likely in some scenarios.
Doing that would completely change the meaning of the visibility map from a heap visibility map into an index-only map. IndexOnly scans would still work, but nothing else would ever and it would be hard to confirm the validity of the vm. -1 -- Simon Riggs 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
