Re: Standbys, txid_current_snapshot, wraparound

On Wed, Mar 28, 2012 at 10:54:58PM +0100, Simon Riggs wrote:
> On Wed, Mar 28, 2012 at 10:24 PM, Simon Riggs <simon(at)2ndquadrant(dot)com> wrote:
> > On Wed, Mar 28, 2012 at 9:48 PM, Marko Kreen <markokr(at)gmail(dot)com> wrote:
> >> On Fri, Mar 23, 2012 at 08:52:40AM +0000, Simon Riggs wrote:
> >>> Master pg_controldata - OK txid_current_snapshot() - OK
> >>> Standby pg_controldata - OK txid_current_snapshot() - lower value
> >>
> >> On Skytools list is report about master with slaves, but the
> >> lower value appears on master too:
> >>
> >>  http://lists.pgfoundry.org/pipermail/skytools-users/2012-March/001601.html
> >>
> >> Cc'd original reporter too.
> >
> > Thanks. Am looking.
>
> I can't see how this could happen on the master at all.
>
> On the standby, it can happen if we skip restartpoints for about a
> couple of billion xids. Which would be a problem.
>
> More on this tomorrow.

I can't find a place where WAL replay updates values under XLogCtl.
If that really does not happen, that would explain why standbys can
see wrong epoch.

No clue yet how master can get broken.

--
marko