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
