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

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?

--
Magnus Hagander
Me: http://www.hagander.net/
Work: http://www.redpill-linpro.com/