Re: BUG #14230: Wrong timeline returned by pg_stop_backup on a standby

On Mon, Jul 11, 2016 at 3:31 PM, Magnus Hagander <magnus(at)hagander(dot)net> wrote:
>
>
> On Thu, Jul 7, 2016 at 8:38 AM, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>
> wrote:
>>
>> On Thu, Jul 7, 2016 at 12:57 AM, Marco Nenciarini
>> <marco(dot)nenciarini(at)2ndquadrant(dot)it> wrote:
>> > After further analysis, the issue is that we retrieve the starttli from
>> > the ControlFile structure, but it was using ThisTimeLineID when writing
>> > the backup label.
>> >
>> > I've attached a very simple patch that fixes it.
>>
>> ThisTimeLineID is always set at 0 on purpose on a standby, so we
>> cannot rely on it (well it is set temporarily when recycling old
>> segments). At recovery when parsing the backup_label file there is no
>> actual use of the start segment name, so that's only a cosmetic
>> change. But surely it would be better to get that fixed, because
>> that's useful for debugging.
>>
>> While looking at your patch, I thought that it would have been
>> tempting to use GetXLogReplayRecPtr() to get the timeline ID when in
>> recovery, but what we really want to know here is the timeline of the
>> last REDO pointer, which is starttli, and that's more consistent with
>> the fact that we use startpoint when writing the backup_label file. In
>> short, +1 for this fix.
>>
>> I am adding that in the list of open items, adding Magnus in CC whose
>> commit for non-exclusive backups is at the origin of this defect.
>
>
> I agree this looks correct.
>
> But isn't this also a pre-existing bug in 9.5? Or did we change something
> else that suddenly made it visible?
>

I think the bug is pre-existing, but it becomes visible to user now by new API.

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com