| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Josh Berkus <josh(at)agliodbs(dot)com> |
| Cc: | postgres hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Idea for getting rid of VACUUM FREEZE on cold pages |
| Date: | 2010-05-22 13:35:29 |
| Message-ID: | 1787.1274535329@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Josh Berkus <josh(at)agliodbs(dot)com> writes:
> From a discussion at dinner at pgcon, I wanted to send this to the list
> for people to poke holes in it:
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.
regards, tom lane
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