On 2/27/19 4:48 PM, Achilleas Mantzios wrote:
> On 27/2/19 4:16 μ.μ., David Steele wrote:
>> On 2/27/19 2:31 PM, Achilleas Mantzios wrote:
>>> On 27/2/19 1:58 μ.μ., richter@simkorp.com.br wrote:
>>>> Just to notice, I d o use backup from standby and WAL archive from
>>>> standby. It is possible. But you have to configure standby with
>>>> option of wal archive "always".
>>>
>>> I guess there are issues with it. If this was so easy then pgbarman
>>> and pgbackrest would support it out of the box.
>>
>> There are a few issues with it:
>>
>> 1) If you allow the primary and standby to archive to the same
>> repository then there needs to be some conflict resolution if they
>> write at the same time. If they write to different repositories then
>> you need to decided which one to use for a restore, or have some kind
>> of conflict resolution between them. It gets complicated.
>>
>> 2) Writing only from the standby reduces load on the primary but if
>> the connection to the primary is down then you can get behind on
>> archiving. If something then happens to the primary then your recovery
>> point will be limited.
>
> David to quote an older email from you:
> "pgBackRest currently requires some files and all WAL to be sent from
> the primary even when doing backup from standby. We may improve this in
> the future but it's not on the road map right now. "
> So, I had the impression that receiving WALs from the standby was a
> greater technical problem.
No, it just increases the risk of being behind on archiving.
One of the things pgBackRest does well is move a *lot* of WAL and it is
orders of magnitude faster than streaming replication, which is
single-threaded and uncompressed. So, in spite of the additional load
it's generally safest to archive from the primary, especially on high
write volume clusters.
--
-David
david@pgmasters.net