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From Jonathan Colby <>
Subject Quorum, Hector, and datacenter preference
Date Thu, 24 Mar 2011 13:02:58 GMT
Hi -

Our cluster is spread between 2 datacenters.   We have a straight-forward IP assignment so
that OldNetworkTopology (rackinferring snitch) works well.    We have cassandra clients written
in Hector in each of those data centers.   The Hector clients all have a list of all cassandra
nodes across both data centers.  RF=3.

Is there an order as to which data center gets the first write?    In other words, would (or
can) the Hector client do its first write to the cassandra nodes in its own data center?

It would be ideal it Hector chose the "local" cassandra nodes.  That way, if one data center
is unreachable, the Quorum of replicas in cassandra is still reached (because it was written
to the working data center first).

Otherwise, if the cassandra writes are really random from the Hector client point-of-view,
a data center outage would result in a read failure for any data that has 2 replicas in the
lost data center.

Is anyone doing this?  Is there a flaw in my logic?

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