could you clarify this statement. mongodb native is consistent and atomic wrt to single documents. Are you saying that tokumx does something additional wrt to transactions (which also implies client api changes)?
TokuMX offers multi-document transactional semantics without application changes (snapshot reads), as well as protocol support for multi-statement (read-modify-write style) transactions, within a single shard. We are still designing how we want to present transactions in a sharded cluster.