Re: pg_upgrade < 9.3 -> >=9.3 misses a step around multixacts

Bruce Momjian wrote:
> On Thu, Jun 19, 2014 at 06:12:41PM -0400, Alvaro Herrera wrote:
> > BTW I hacked up pg_resetxlog a bit to make it generate the necessary
> > pg_multixact/offset file when -m is given. This is not acceptable for
> > commit because it duplicates the #defines from pg_multixact.c, but maybe
> > we want this functionality enough that we're interested in a more
> > complete version of this patch; also it unconditionally writes one zero
> > byte to the file, which is of course wrong if the file exists and
> > already contains data.
>
> Why would we want this if the system functions fine without those files
> being created? I don't think we want pg_resetxlog to be doing anything
> except changing pg_controldata.

I don't understand why you say the system functions fine. If you move
the multixactid with pg_resetxlog to a point which doesn't have the
necessary file and page, the system will not start. Only pg_upgrade
knows to create the file appropriately, but normal operation doesn't.

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