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

On Fri, Jun 20, 2014 at 02:24:55PM -0400, Tom Lane wrote:
> Bruce Momjian <bruce@momjian.us> writes:
> > On Fri, Jun 20, 2014 at 01:41:42PM -0400, Tom Lane wrote:
> >> Yeah.  In my mind, at least, there's been a TODO for some time for
> >> pg_resetxlog to make sure that pg_clog and the other SLRU-like files
> >> get populated appropriately when you tell it to change those counters.
> >> You have to have a segment file at the right place or startup fails.
>
> > Well, if we are going to do this, we had better do all cases or the
> > behavior will be quite surprising, and when doing disaster recovery,
> > surprises are not good.  I am a little worried that removing files as
> > part of pg_resetxlog might cause data to be lost as users try to figure
> > things out.
>
> Huh?  The basic charter of pg_resetxlog is to throw away files, ie, all
> of your WAL.
>
> But in this case what we're talking about is a secondary function, namely
> the ability to move the XID, MXID, etc counter values.  Up to now, if you
> did that, it was on your head to manually create appropriate SLRU segment
> files.  It's certainly less error-prone, not more so, if the code were
> to take care of that for you.

I am fine with that, but let's do a complete job so the user API is not
confusing.

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

  + Everyone has their own god. +