Re: recovery starting when backup_label exists, but not recovery.signal

On 9/27/19 4:41 AM, Fujii Masao wrote:
> On Fri, Sep 27, 2019 at 4:07 PM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>>
>> On Fri, Sep 27, 2019 at 3:36 AM David Steele <david(at)pgmasters(dot)net> wrote:
>>>
>>> On 9/24/19 1:25 AM, Fujii Masao wrote:
>>>>
>>>> When backup_label exists, the startup process enters archive recovery mode
>>>> even if recovery.signal file doesn't exist. In this case, the startup process
>>>> tries to retrieve WAL files by using restore_command. Then, at the beginning
>>>> of the archive recovery, the contents of backup_label are copied to pg_control
>>>> and backup_label file is removed. This would be an intentional behavior.
>>>
>>>> But I think the problem is that, if the server shuts down during that
>>>> archive recovery, the restart of the server may cause the recovery to fail
>>>> because neither backup_label nor recovery.signal exist and the server
>>>> doesn't enter an archive recovery mode. Is this intentional, too? Seems No.
>>>>
>>>> So the problematic scenario is;
>>>>
>>>> 1. the server starts with backup_label, but not recovery.signal.
>>>> 2. the startup process enters an archive recovery mode because
>>>> backup_label exists.
>>>> 3. the contents of backup_label are copied to pg_control and
>>>> backup_label is deleted.
>>>
>>> Do you mean deleted or renamed to backup_label.old?
>>>
>>>> 4. the server shuts down..
>>>
>>> This happens after the cluster has reached consistency?
>>>
>>>> 5. the server is restarted. neither backup_label nor recovery.signal exist.
>>>> 6. the startup process starts just crash recovery because neither backup_label
>>>> nor recovery.signal exist. Since it cannot retrieve WAL files from archival
>>>> area, it may fail.
>>>
>>> I tried a few ways to reproduce this but was not successful without
>>> manually removing WAL.
>>
>> Hmm me too. I think that since we enter crash recovery at step #6 we
>> don't retrieve WAL files from archival area.
>>
>> But I reproduced the problem Fujii-san mentioned that the restart of
>> the server during archive recovery causes to the crash recovery
>> instead of resuming the archive recovery.
>
> Yes, it's strange and unexpected to start crash recovery
> when restarting archive recovery. Archive recovery should
> start again in that case, I think.

+1

--
-David
david(at)pgmasters(dot)net