In this¹ debate, there seemed to be consensus on the following fact: "In Cassandra, say you use N=3, W=3 & R=1. Let’s say you managed to only write to replicas A & B, but not C. In this case Cassandra will return an error to the application saying the write failed- which is acceptable given than W=3. But Cassandra does not cleanup/rollback the writes that happened to A & B."
If this is still true (even for ConsistencyLevel.ALL) then I would like to add it to the API documentation. I'd also be curious about if there have been discussions about for an optional 2PC mode for use on fast LANs. Paul Prescod ¹ http://jsensarma.com/blog/2009/11/dynamo-part-i-a-followup-and-re-rebuttals/
