| From: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | pgsql-hackers(at)postgresql(dot)org, Hannu Krosing <hannu(at)skype(dot)net> |
| Subject: | Re: The vacuum-ignore-vacuum patch |
| Date: | 2006-07-28 04:05:22 |
| Message-ID: | 20060728040522.GD21610@surnet.cl |
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| Thread: | |
| Lists: | pgsql-hackers pgsql-patches |
Tom Lane wrote:
> Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> > Tom Lane wrote:
> >> nonInVacuumXmin seems useless ... perhaps a vestige of some earlier
> >> version of the computation?
>
> > Hmm, not useless at all really -- only a bug of mine. Turns out the
> > notInVacuumXmin stuff is essential, so I put it back.
>
> Uh, why?
Because it's used to determine the Xmin that our vacuum will use. If
there is a transaction whose Xmin calculation included the Xid of a
transaction running vacuum, we have gained nothing from directly
excluding said vacuum's Xid, because it will affect us anyway indirectly
via that transaction's Xmin.
--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.
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