FWIW, I don't think Cassandra is particularly any better today semantically than it used to be. Merge conflicts are still at the cell level than the row level,

FWIW, I don't think Cassandra is particularly any better today semantically than it used to be. Merge conflicts are still at the cell level than the row level, and wall-clock time is still the way that LWW resolution is determined. It let's you mix strongly consistent and eventually consistent data together, which makes no sense. But the difference is that Cassandra is reliably "broken" in those ways, and as a result there are ways of using it which don't lean heavily on those weaknesses. Such as writing only immutable data or isolating all data that will be used in paxos transactions into their own column families by convention, etc. Cassandra more or less behaves exactly as it claims that it does. So you can do a somewhat thorough investigation of its system semantics and know what you can rely on and what you can't. MongoDB doesn't even uphold the system semantics it claims that it has, so it's just broken in weird and esoteric ways that you discover mostly by accident.