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From Peter Schuller <>
Subject Re: Multi DC setup
Date Tue, 11 Oct 2011 07:36:17 GMT
> We already have two separate rings. Idea of bidirectional sync is, if one
> ring is down, we can still send the traffic to other ring. When original
> cluster comes back, it will pick up the data from available cluster. I'm not
> sure if it makes sense to have separate rings or combine these two rings
> into one.

Cassandra doesn't have support for synchronizing data between two
different rings. The multi-dc support in Cassandra amounts to having a
single ring containing all nodes from all data centers. Cassandra is
told (by configuring the snitch, such as through a property files)
which nodes are in which data center. Using the
NetworkTopologyStrategy, you then make sure to distribute replicas in
DC:s as you see fit.

Cassandra will then prefer local nodes for read and write operations,
and you can use e.g. LOCAL_QUORUM consistency level to get quorum like
consistency within a DC.

Google/check wiki/read docs about NetworkTopologyStrategy and
PropertyFileSnitch. I don't have a good link to multi-dc off hand
(anyone got a good link to suggest that goes through this?).

/ Peter Schuller (@scode on twitter)

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