Re: Re: [COMMITTERS] pgsql: Make CheckRequiredParameterValues() depend upon correct - Mailing list pgsql-hackers

On Tue, Apr 27, 2010 at 6:49 PM, Heikki Linnakangas
<heikki.linnakangas@enterprisedb.com> wrote:
> Fujii Masao wrote:
>> config.sgml
>>> <literal>on</literal>.  It is thought that there is little
>>> measurable difference in performance from using this feature, so
>>> feedback is welcome if any production impacts are noticeable.
>>> It is likely that this parameter will be removed in later releases.
>>
>> Is this description still required for recovery_connections?
>
> Hmm, I guess it was referring to setting recovery_connections in the
> master, I don't see us removing that option from the standby in the
> future. recovery_connections in the master is being replaced with the
> wal_mode setting, so I guess that's not required anymore.

Agreed.

>>> if (!XLogArchivingActive())
>>>   ereport(ERROR,
>>>     (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
>>>      errmsg("WAL archiving is not active"),
>>>      errhint("archive_mode must be enabled at server start.")));
>>
>> You need to change the error messages which refer to archive_mode,
>> like the above.
>
> Hmm, I think we should change not only the error message, but the logic
> too. There's two related checks there:
>
>>       if (!XLogArchivingActive())
>>               ereport(ERROR,
>>                               (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
>>                                errmsg("WAL archiving is not active"),
>>                                errhint("archive_mode must be enabled at server start.")));
>>
>>       if (!XLogArchiveCommandSet())
>>               ereport(ERROR,
>>                               (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
>>                                errmsg("WAL archiving is not active"),
>>                                errhint("archive_command must be defined before "
>>                                                "online backups can be made safely.")));
>
> You can use streaming replication too to transport the WAL generated
> during the backup, so I think we should just check that wal_mode>='archive'.

It's OK in pg_start_backup(), but seems NG in pg_stop_backup() since
it waits until some WAL files have been archived by the archiver. No?

>> + /*
>> +  * For Hot Standby, the WAL must be generated with 'hot_standby' mode,
>> +  * and we must have at least as many backend slots as the primary.
>> +  */
>> + if (InArchiveRecovery && XLogRequestRecoveryConnections)
>> + {
>> +   if (ControlFile->wal_mode < WAL_MODE_HOT_STANDBY)
>> +       ereport(ERROR,
>> +              (errmsg("recovery connections cannot start because
>> wal_mode was not set to 'hot_standby' on the WAL source server")));
>>
>> This seems to always prevent the server from doing an archive recovery
>> since wal_mode is expected to be WAL_MODE_ARCHIVE in that case.
>
> No, it doesn't prevent archive recovery. It only prevents hot standby if
> wal_mode was not 'hot_standby' in the master. I think you missed the "&&
> XLogRequestRecoveryConnections" condition above.

Even if we do only archive recovery, XLogRequestRecoveryConnections
might be TRUE. Or we need to ensure that the recovery_connection is
FALSE in the postgresql.conf before starting archive recovery?

And I tried archive recovery, and encountered the following error.
 LOG:  starting archive recovery LOG:  restored log file "000000010000000000000001" from archive FATAL:  recovery
connectionscannot start because wal_mode was not 
set to 'hot_standby' on the WAL source server LOG:  startup process (PID 32512) exited with exit code 1 LOG:  aborting
startupdue to startup process failure 

XLOG-related parameters in postgresql.conf archive_mode = on archive_command = 'cp %p ../data.arh/%f' wal_mode =
archiverecovery_connections = on 

Regards,

--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center