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From Jonathan Colby <jonathan.co...@gmail.com>
Subject Re: Quorum and Datacenter loss
Date Sun, 12 Dec 2010 15:42:20 GMT
Thanks a lot Peter.   So basically we would need to choose a
consistency other than QUORUM.    I think in our case consistency is
not necessarily an issue since our data is write-once, read-many
(immutable data).   I suppose having a replication factor of 4 would
result in two nodes in each datacenter having a copy of the data.   If
there's a flaw in my logic, please let me know : ]

On Sun, Dec 12, 2010 at 2:04 PM, Peter Schuller
<peter.schuller@infidyne.com> wrote:
>>> Is my logic wrong here?  Is there a way to ensure the nodes in the
>>> alive datacenter respond successfully if the second datacenter is
>>> lost?  Anyone have experience with this kind of problem?
>>
>> It's impossible to achieve the consistency and availability at the
>> same time. See:
>
> (Assuming partition tolerance)
>
> Anyways, to expand a bit: The final consequence is that if you have a
> cluster that really does need QUORUM consistency, you won't be able to
> survive (in terms of availability, i.e., the cluster serving your
> traffic) data centers going down. If you want to continue operating in
> the case of a partition, you (1) cannot use QUORUM and (2) your
> application must be designed to work with and survive seeing
> inconsistent data.
>
> --
> / Peter Schuller
>

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