Re: Re: BUG #12990: Missing pg_multixact/members files (appears to have wrapped, then truncated) - Mailing list pgsql-bugs

From Alvaro Herrera
Subject Re: Re: BUG #12990: Missing pg_multixact/members files (appears to have wrapped, then truncated)
Date
Msg-id 20150507183950.GH2523@alvh.no-ip.org
Whole thread Raw
In response to Re: Re: BUG #12990: Missing pg_multixact/members files (appears to have wrapped, then truncated)  (Robert Haas <robertmhaas@gmail.com>)
List pgsql-bugs
Robert Haas wrote:
> On Thu, May 7, 2015 at 2:00 PM, Alvaro Herrera <alvherre@2ndquadrant.com> wrote:

> > I considered this question in the previous commit: is it okay to
> > overwrite a file that is no longer used (per the limits set by vacuum)
> > but not yet removed (by checkpoint)?  It seems to me that there is no
> > data-loss issue with doing that -- which is why the advance-oldest code
> > is called during vacuum and not during checkpoint.
>
> I think the main question is whether truncation will be smart enough
> to zap the non-overwritten part of the old stuff but not the part that
> did get overwritten.

TruncateMultiXact bases its removal of member files on the point set by
checkpoint, MultiXactState->lastCheckpointedOldest.  I tested this back
then and there was no issue.

--
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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