>>neolef+K8
Cassandra offers a mix of commutative operations (sets, maps, increments), an eventlog model, and lightweight (paxos-based) transactions. Unlike a key/value database like Riak, Cassandra can update individual fields of a row or document independently, which simplifies things enormously.
http://www.datastax.com/dev/blog/why-cassandra-doesnt-need-v...
http://www.datastax.com/dev/blog/cql3_collections
http://www.datastax.com/dev/blog/lightweight-transactions-in...