Consistency
ANY
- any server (may not be replica)
- Fastest: coordinator caches write and replies quickly to client
ALL
- all replicas
- Ensures strong consistency, but slowest
ONE
- at least one replica
- Faster than ALL, but cannot tolerate a failure
QUORUM
- quorum across all replicas in all datacenters
- Majority > 50%
- Quorums faster than ALL, but still ensure strong consistency
- Several key-value/NoSQL stores (e.g., Riak and Cassandra) use quorums
Types of Consistency
- Cassandra offers Eventual Consistency