Now you are arguing about a lack of a particular builtin feature. Riak is last-write-wins by default with optional vector clocks and builtin CRDTs. Cassandra is last-write-wins by default with clustering columns allowing to implement an equivalent of Riak vector clocks and CRDTs in the application. If you include a client id in the primary key and use client-side timestamps, you essentially are doing vector clocks and there are no conflicts guaranteed - users of Cassandra have been doing it for years.