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From Paolo Negri <hungrybl...@gmail.com>
Subject Re: Replication and sequence id question
Date Tue, 16 Apr 2013 12:48:17 GMT
Thanks again for the answer, I'm now confused by the role of the
checkpoint and its storage, let's say that I have a mobile app that
has been downloaded on 100k devices and I'm using touchdb to sync my
db to the devices, does this mean that each device will need to store
a checkpoint on my server side database, so that I'd end up with 100k
local documents in the database each one belonging to one of the
clients?

Paolo

On Tue, Apr 16, 2013 at 1:23 PM, Robert Newson <rnewson@apache.org> wrote:
> 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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