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From Rajkumar Gupta <rajkumar....@gmail.com>
Subject Re: meaning of eventual consistency in Cassandra ?
Date Mon, 03 Jan 2011 19:13:13 GMT
This means that nodes in cassandra cluster contain data that has been
sharded onto serveral nodes as well as this sharded data may be
replicated further across several nodes ? So cassandra storage
utilizes both sharded as well as replication for load balancing? Is
this correct ?

On Mon, Jan 3, 2011 at 11:28 PM, Peter Schuller
<peter.schuller@infidyne.com> wrote:
>> What is the meaning of eventual consistency in Cassandra when nodes in
>> a single cluster do not mantain the copies of same data but rather
>> data is distributed among nodes. Since a single peice of data is
>> recorded at a single place(node),Why wouldn't Cassandra return the
>> recent value from that single place of record? How do multiple copies
>> arise in this situation ? Where are the replicas in Cassandra cluster
>> ?
>
> There is normally not just a single copy. If you run with RF
> (replication factor) = 1, you have a single copy. But this is only
> useful if you don't care about redundancy at all.
>
> With multiple replicas, the consistency depends on what you're doing.
> For example the choice of consistency level (see the levels listed on
> http://wiki.apache.org/cassandra/API).
>
> However note that even with RF=1, there are some things that are still
> only "eventual". For example if you submit a batch mutation,
> concurrent readers may see a partially applied batch mutation for a
> given row even though it is only being written to a single node.
>
> --
> / Peter Schuller
>

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