Re: txid failed epoch increment, again, aka 6291

On Tue, Sep 04, 2012 at 09:46:58AM -0700, Daniel Farina wrote:
> I might try to find the segments leading up to the overflow point and
> try xlogdumping them to see what we can see.

That would be helpful to see.

Just to grasp at yet-flimsier straws, could you post (URL preferred, else
private mail) the output of "objdump -dS" on your "postgres" executable?

> If there's anything to note about the workload, I'd say that it does
> tend to make fairly pervasive use of long running transactions which
> can span probably more than one checkpoint, and the txid reporting
> functions, and a concurrency level of about 300 or so backends ... but
> per my reading of the mechanism so far, it doesn't seem like any of
> this should matter.

Thanks for the details; I agree none of that sounds suspicious.

After some further pondering and testing, this remains a mystery to me.  These
symptoms imply a proper update of ControlFile->checkPointCopy.nextXid without
having properly updated ControlFile->checkPointCopy.nextXidEpoch.  After
recovery, only CreateCheckPoint() updates ControlFile->checkPointCopy at all.
Its logic for doing so looks simple and correct.