Yes, `leveldb.write` is synchronous and it throws an exception on failure. This will restart the journal, receive the next `Write` and the processor will never see message for which writing failed. 

If a client wants to have a confirmation that a write actually succeeded it should expect an (application-level) reply from a processor. What a journal could do is to publish a `WriteFailed` to the event bus in case of a `leveldb.write` failure.