| From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
|---|---|
| To: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: GetOldestXmin going backwards is dangerous after all |
| Date: | 2013-02-04 17:29:15 |
| Message-ID: | 20130204172915.GD22226@awork2.anarazel.de |
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| Lists: | pgsql-hackers |
On 2013-02-04 17:21:50 +0000, Simon Riggs wrote:
> On 4 February 2013 17:02, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
>
> > I unfortunately don't yet see a robust way without storing the last used
> > horizon :(.
>
> We can't go backwards, but we can go forwards.
>
> We can move the next xid forwards by an amount equal to the increase
> in vacuum_defer_cleanup_age.
Don't think that helps, the problem is not new writes but already
removed rows in the toast table.
Besides, advancing the next xid by vacuum_defer_cleanup_age every
restart could get expensive. Unless we find a space to store the old
value which we haven't really got in the back branches (control file?)...
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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