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From Paolo Negri <hungrybl...@gmail.com>
Subject Re: Replication and sequence id question
Date Tue, 16 Apr 2013 09:06:44 GMT
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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