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From Jonathan Colby <>
Subject how does cassandra pick its replicant peers?
Date Fri, 25 Mar 2011 22:00:19 GMT

Does anyone know how cassandra chooses the nodes for its other replicant copies?

The first node gets the first copy because its token is assigned for that key.   But what
about the other copies of the data?

Do the replicant nodes stay the same based on the token range?  Or are the other copies send
to any random node based on its load and availability?

I think this is important in order to understand because it affects how to plan for situations
where a significant number of nodes are suddenly unavailable, such as the loss of a data center.

If the replicants are copied just based on random availability, then quorum writes could survive
on the remaining nodes.  But if the replicant nodes are somehow pre-determined, those replicants
may node be available and writes will fail.

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