FWIW, we were able to integrate Druid and Cassandra.  

Its only in PoC right now, but it seems like a powerful combination:
http://brianoneill.blogspot.com/2013/05/cassandra-as-deep-storage-mechanism-for.html

-brian

--
Brian ONeill
Lead Architect, Health Market Science (http://healthmarketscience.com)
mobile:215.588.6024
blog: http://brianoneill.blogspot.com/
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