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

On Fri, May 30, 2014 at 05:13:17PM +0200, Andres Freund wrote:
> On 2014-05-30 11:00:06 -0400, Bruce Momjian wrote:
> > On Fri, May 30, 2014 at 03:32:44PM +0200, Andres Freund wrote:
> > > On 2014-05-30 09:29:16 -0400, Bruce Momjian wrote:
> > > > This is a bug in 9.3 pg_upgrade as well?
> > >
> > > Yes.
> > >
> > > >  Why has no one reported it before?
> > >
> > > My guess is that it wasn't attributed to pg_upgrade in the
> > > past. Typically the error will only occur a fair amount of time
> > > later. You'll just see vacuums randomly erroring out with slru.c errors
> > > about nonexistant files :(.
> >
> > But how much later?  pg_upgrade is pretty popular now but I am just not
> > seeing the number of errors as I would expect:
> >
> >     ERROR: could not access status of transaction 2072053907
> >     DETAIL: Could not open file "pg_multixact/offsets/7B81": No such file or directory.
>
> > I am not saying there is no bug, but from your analysis it would seem to
> > be 100% of pg_upgrade'ed clusters that use multi-xacts.
>
> It'd need to be clusters that used more multixacts than fit onto two
> slru offsets/ segments in < 9.2. Otherwise things will probably just
> continue to work because there's no hole.

Do you mean <= 9.2 here for the old cluster?  Multi-xacts were added in
9.3:

        commit 0ac5ad5134f2769ccbaefec73844f8504c4d6182
        Author: Alvaro Herrera <alvherre@alvh.no-ip.org>
        Date:   Wed Jan 23 12:04:59 2013 -0300

            Improve concurrency of foreign key locking

--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + Everyone has their own god. +