The current buffer(..) methods are non-blocking, but do not return anything (return type void). With the addition of the async API and the switch to Java 8, having an async version of these methods that would return an ApiFuture<Void> would simplify writing chained async statements for a transaction. The semantics of the async versions would be exactly the same as the current methods, as those are already non-blocking, but it would make it possible to clean up client code.