Re: Hot Backup with rsync fails at pg_clog if under load

On Oct27, 2011, at 16:30 , Simon Riggs wrote:
> On Thu, Oct 27, 2011 at 3:03 PM, Florian Pflug <fgp(at)phlo(dot)org> wrote:
>
>>> I think you make a good case for doing this.
>>>
>>> However, I'm concerned that moving LogStandbySnapshot() in a backpatch
>>> seems more risky than it's worth. We could easily introduce a new bug
>>> into what we would all agree is a complex piece of code. Minimal
>>> change seems best in this case.
>>
>> OTOH, we currently compute oldestActiveXid within LogStandbySnapshot().
>> Your proposed patch changes that, which also carries a risk since something
>> could depend on these values being in sync. Especially since both the logged
>> snapshot and oldestActiveXid influence the snapshot tracking on the slave.
>>
>> But since you wrote most of that code, your judgement about the relative
>> risks of these two approaches obviously out-weights mine.
>
> We must move oldestActiveXid since that is the source of a bug. There
> is no need to move LogStandbySnapshot(), so I am suggesting we don't
> do that for the backpatch. I was going to implement it the way you
> suggest in HEAD, since I agree that is a cleaner way.

Sound good.

best regards,
Florian Pflug