Re: Re: [GENERAL] 9.4.1 -> 9.4.2 problem: could not access status of transaction 1

On Thu, May 28, 2015 at 07:24:26PM -0400, Robert Haas wrote:
> On Thu, May 28, 2015 at 4:06 PM, Joshua D. Drake <jd@commandprompt.com> wrote:
> > FTR: Robert, you have been a Samurai on this issue. Our many thanks.
>
> Thanks!  I really appreciate the kind words.
>
> So, in thinking through this situation further, it seems to me that
> the situation is pretty dire:
>
> 1. If you pg_upgrade to 9.3 before 9.3.5, then you may have relminmxid
> or datminmxid values which are 1 instead of the correct value.
> Setting the value to 1 was too far in the past if your MXID counter is
> < 2B, and too far in the future if your MXID counter is > 2B.
>
> 2. If you pg_upgrade to 9.3.7 or 9.4.2, then you may have datminmxid
> values which are equal to the next-mxid counter instead of the correct
> value; in other words, they are two new.
>
> 3. If you pg_upgrade to 9.3.5, 9.3.6, 9.4.0, or 9.4.1, then you will
> have the first problem for tables in template databases, and the
> second one for the rest. (See 866f3017a.)

I think we need to step back and look at the brain power required to
unravel the mess we have made regarding multi-xact and fixes.  (I bet
few people can even remember which multi-xact fixes went into which
releases --- I can't.)  Instead of working on actual features, we are
having to do this complex diagnosis because we didn't do a thorough
analysis at the time a pattern of multi-xact bugs started to appear.
Many projects deal with this compound bug debt regularly, but we have
mostly avoided this fate.

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

  + Everyone has their own god. +