Re: [BUG] pg_basebackup from disconnected standby fails

On Tue, Jun 14, 2016 at 8:31 PM, Kyotaro HORIGUCHI
<horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
>> +# Take a second backup of the standby while the master is offline.
>> +$node_master->stop;
>> +$node_standby_1->backup('my_backup_2');
>> +$node_master->start;
>
> I'm not sure that adding the test case for a particular bug like
> this is appropriate. But it would be acceptable because it
> doesn't take long time and it is separate from standard checks.

We already take a backup from a standby when master is connected, it
should not cost much in terms of time.

> It seems to me that we could more agressively advance the
> minRecoveryPoint (but must not let it go too far..), but it is
> right for it to aim a bit smaller than the ideal location.

It may be risky to propose such a change for a backpatch. Anyway, in
any case there is no guarantee that when using the low-level backup
routines pg_start/stop_backup with a custom backup method the minimum
recovery point will be correct.. pg_basebackup does that a bit more
carefully if I recall correctly (too lazy to look at the code now :)).
--
Michael