&gt; Could the service have committed more messages than it acknowledged?<p>Yes of course. It may have committed records but not had time to to ACK success.<p>&gt; Or many less than I&#x27;ve sent?<p>Yes again. However it will NEVER ACK success for writes which it hasn&#x27;t committed.<p>So the persistence story is pretty straightforward (I&#x27;ll see if we can update docs if this is missing).<p>If you want to avoid duplication on the write side, you would have to retrieve the last log record-- with id x-- and start adding records again from id x+1.<p>Fencing + locking combine to provide efficient exclusive access and the fat client (for now) guarantees write ordering.