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

On 06/07/16 17:37, Marco Nenciarini wrote:
> Hi,
>
> On 06/07/16 17:07, francesco(dot)canovai(at)2ndquadrant(dot)it wrote:
>> The following bug has been logged on the website:
>>
>> Bug reference: 14230
>> Logged by: Francesco Canovai
>> Email address: francesco(dot)canovai(at)2ndquadrant(dot)it
>> PostgreSQL version: 9.6beta2
>> Operating system: Linux
>> Description:
>>
>> I'm taking a concurrent backup from a standby in PostgreSQL beta2 and I get
>> the wrong timeline from pg_stop_backup(false).
>>
>> This is what I'm doing:
>>
>> 1) I set up an environment with a primary server and a replica in streaming
>> replication.
>>
>> 2) On the replica, I run
>>
>> postgres=# SELECT pg_start_backup('test_backup', true, false);
>> pg_start_backup
>> -----------------
>> 0/3000A00
>> (1 row)
>>
>> 3) When I run pg_stop_backup, it returns a start wal location belonging to a
>> file with timeline 0.
>>
>> postgres=# SELECT pg_stop_backup(false);
>> pg_stop_backup
>>
>> ---------------------------------------------------------------------------
>> (0/3000AE0,"START WAL LOCATION: 0/3000A00 (file
>> 000000000000000000000003)+
>> CHECKPOINT LOCATION: 0/3000A38
>> +
>> BACKUP METHOD: streamed
>> +
>> BACKUP FROM: standby
>> +
>> START TIME: 2016-07-06 16:44:31 CEST
>> +
>> LABEL: test_backup
>> +
>> ","")
>> (1 row)
>>
>> The timeline returned is fine (is 1) when running the same commands on the
>> master.
>>
>> An incorrect backup label doesn't prevent PostgreSQL from starting up, but
>> it affects the tools using that information.
>>
>>
>
> The issue here is that the do_pg_stop_backup function uses the
> ThisTimeLineID variable that is not valid on standbys.
>
> I think that it should read it from
> ControlFile->checkPointCopy.ThisTimeLineID as we do in do_pg_start_backup.
>

No, that's not the solution.

The backup_label is generated during the do_pg_start_backup call, so
also the copy in ControlFile->checkPointCopy.ThisTimeLineID is
uninitialized.

Regards,
Marco

--
Marco Nenciarini - 2ndQuadrant Italy
PostgreSQL Training, Services and Support
marco(dot)nenciarini(at)2ndQuadrant(dot)it | www.2ndQuadrant.it