As far as datastores go, cassandra is write-optimized. Writes are faster than reads. So for this use case (heavy denormalization) it is a good fit. Also, Cass

As far as datastores go, cassandra is write-optimized. Writes are faster than reads. So for this use case (heavy denormalization) it is a good fit. Also, Cassandra reduces the operational complexity of having a logical store which spans multiple hosts. Your memcache example does not get persistence for free, and sharding mysql is something you have to do manually. The interface to a Cassandra cluster is the same regardless of how many nodes you are running. Scaling writes is "hard". Incrementing counters is obviously write heavy, and cassandra aims to make it easier.