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From Robert Newson <rnew...@apache.org>
Subject Re: Replication and sequence id question
Date Tue, 16 Apr 2013 11:23:38 GMT
Hi Paolo,

The checkpoint is stored in the database at source and target, so
couchdb will fail to find that document on server B and so it will
start from update sequence 0.

B.

On 16 April 2013 10:06, Paolo Negri <hungryblank@gmail.com> wrote:
> Hi Robert
>
> On Tue, Apr 16, 2013 at 10:05 AM, Robert Newson <rnewson@apache.org> wrote:
>> Hi Paolo,
>>
>> No, couchdb (and touchdb) will be just fine if you fail over to a
>> different server. What will happen is that the replication from server
>> B to your mobile client will start from update sequence 0 (as you will
>> have no previous checkpoint).
>
> I'm wondering what happens if the fallback is not explicit to the
> client let's say I have the database exposed under
> https://mydomain.com/mydatabase and under this url usually respond
> server A but after the failover requests are instead forwarded
> internally to server B won't the mobile client be looking for the
> checkpoint of server A and be confused about the fact of being talking
> with server B instead?
>
>> The replication process will then check
>> whether each update on server B is on your client already. If the A to
>> B replication is still running, then the majority of updates you get
>> from server B will already be present on your mobile device. Any that
>> are missing will be replicated.
>>
>> You can freely replicate from multiple servers to your mobile client, it works.
>>
>> B.
>>
>> On 16 April 2013 08:43, Paolo Negri <hungryblank@gmail.com> wrote:
>>> Dear list
>>>
>>> I have a question related to couchdb replication, let me walk you
>>> through the scenario
>>>
>>> I have 2 servers server A and server B
>>>
>>> on both A and B I'm running couchdb
>>> B is configured to replicate all dbs from A
>>>
>>> I also have one mobile client that uses touchdb to sync data with one
>>> database on server A
>>>
>>> At some point server A breaks and then the mobile client can't reach A
>>> and then will fallback to B
>>>
>>> What happens in terms of syncing? will the mobile client be confused
>>> by the fact that the database on server B doesn't share sequence
>>> numbers with the same database in A?
>>>
>>> Thanks for your help,
>>>
>>> Paolo

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