Iterating through keys is not trivial in Riak, you need a 2i to have that. If you have the manpower to maintain your solution and there are people with performance engineering skill it is probably good. Riak has very predictable performance and it is easy to tune and rock solid system this is why it is used in several healthcare systems and for the game that has the largest player base at the moment as well. The consistent hashing layer on the top of LevelDB which is essentially the foundation of RocksDB makes it super nice system. Anyways, I hope Keevo will be available for us as well.

The "you need 2i to have that" is too heavy.

See yugabyte that does cassandra+keevo+rocksdb+raft