Re: Lazy xid assignment V3

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?

--
Alvaro Herrera http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.