> Somebody (I think Joe or Heikki) poked a big hole in this last night at
> the Royal Oak. Although the scheme would get rid of the need to replace
> old XIDs with FrozenXid, it does not get rid of the need to set hint
> bits before you can truncate CLOG. So in your example of an insert-only
> table that's probably never read again, there's still a minimum of one
> update visit required on every old page. Now that's still better than
> two update visits ... but we could manage that already, just by tweaking
> vacuum's heuristics about when to freeze vs when to set hint bits.
Yeah, someone pointed that out to me too and suggested that a freeze map
was the better solution. I still think there's something we can do with
pages on the visibility map but I'll have to think about it some more.
-- -- Josh Berkus PostgreSQL Experts Inc.
http://www.pgexperts.com