From: | "Marko Kreen" <markokr(at)gmail(dot)com> |
---|---|
To: | "Alvaro Herrera" <alvherre(at)commandprompt(dot)com> |
Cc: | "Florian G(dot) Pflug" <fgp(at)phlo(dot)org>, PostgreSQL-patches <pgsql-patches(at)postgresql(dot)org> |
Subject: | Re: Lazy xid assignment V3 |
Date: | 2007-09-03 13:15:12 |
Message-ID: | e51f66da0709030615h742fc998nf50549c09c66cba0@mail.gmail.com |
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Lists: | pgsql-patches |
On 9/3/07, Alvaro Herrera <alvherre(at)commandprompt(dot)com> wrote:
> Marko Kreen escribió:
> > On 9/3/07, Alvaro Herrera <alvherre(at)commandprompt(dot)com> wrote:
> > > Florian G. Pflug wrote:
> > > > Since we didn't really reach an agreement on how xid_age should behave,
> > > > I've reverted it back to the original version. So with this patch,
> > > > xid_age will just force assignment of a xid.
> > >
> > > Is this really a good idea? I'm repeating myself, but a query like
> > >
> > > select age(xmin) from bigtable
> > >
> > > could accelerate Xid wraparound. If the server is running close to the
> > > limit it could cause a shutdown to prevent the actual wraparound.
> >
> > Such query would take only one xid, which should not be a problem?
>
> My guess is that it would execute age(xid) once per tuple? Even if all
> the tuples had the same xmin, there's no cache therefore it would
> consume as many Xids as there are tuples.
>
> Am I missing something?
First age() assigns CurrentXid, rest reuse it.
--
marko
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