| From: | Jeff Davis <pgsql(at)j-davis(dot)com> |
|---|---|
| To: | Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov> |
| Cc: | Alvaro Herrera <alvherre(at)commandprompt(dot)com>, Josh Berkus <josh(at)agliodbs(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: [PERFORM] Re: freezing tuples ( was: Why is vacuum_freeze_min_age100m? ) |
| Date: | 2009-08-13 22:24:21 |
| Message-ID: | 1250202261.24981.66.camel@monkey-cat.sm.truviso.com |
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| Lists: | pgsql-hackers pgsql-performance |
On Thu, 2009-08-13 at 17:17 -0500, Kevin Grittner wrote:
> It wouldn't surprise
> me to find workloads where writing data three times (once for the
> data, once for hint bits, and once to freeze the tid)
I'm not sure that we're limited to 3 times, here. I could be missing
something, but if you have tuples with different xmins on the same page,
some might be older than 100M, which you freeze, and then you will have
to come back later to freeze the rest. As far as I can tell, the maximum
number of writes is the number of tuples that fit on the page.
Regards,
Jeff Davis
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