title: Kafka uncommitted messages
body: <p>Lets say the partition has 4 replicas (1 leader, 3 followers) and all are currently in sync. <code>min.insync.replicas</code> is set to 3 and <code>request.required.acks</code> is set to all or -1.</p>
  
  <p>The producer send a message to the leader, the leader appends it to it's log. After that, two of the replicas crashed before they could fetch this message. One remaining replica successfully fetched the message and appended to it's own log.</p>
  
  <p>The leader, after certain timeout, will send an error (NotEnoughReplicas, I think) to the producer since min.insync.replicas condition is not met.</p>
  
  <p>My question is: what will happen to the message which was appended to leader and one of the replica's log? </p>
  
  <p>Will it be delivered to the consumers when crashed replicas come back online and broker starts accepting and committing new messages (i.e. high watermark is forwarded in the log)?</p>