title: Why would the coordinator store hints about dead replicas if a replica node for the row is known to be down ahead of time?
body: <p>According to online docs on datastax (<a href="https://docs.datastax.com/en/cassandra/2.1/cassandra/dml/dml_about_hh_c.html" rel="nofollow noreferrer">https://docs.datastax.com/en/cassandra/2.1/cassandra/dml/dml_about_hh_c.html</a>), the following is stated:</p>
  
  <p><em>During a write operation, when hinted handoff is enabled and consistency can be met, the coordinator stores a hint about dead replicas in the local system.hints table under either of these conditions:</em></p>
  
  <ul>
  <li><em>A replica node for the row is known to be down ahead of time.</em></li>
  <li><em>A replica node does not respond to the write request.</em></li>
  </ul>
  
  <p>What I'm confused is why is the first bullet point a condition why the coordinator would store hints if they already know ahead of time it's down. </p>
  
  <p>According to the docs here(<a href="https://www.datastax.com/dev/blog/how-cassandra-deals-with-replica-failure" rel="nofollow noreferrer">https://www.datastax.com/dev/blog/how-cassandra-deals-with-replica-failure</a>), it states that: <em>the only time Cassandra will fail a write is when too few replicas are alive when the coordinator receives the request.</em></p>
  
  <p>From what I've read so far, hints are utilized only when the required replicas are alive at the time of receiving the request and one or more of the replicas become unresponsive. The first bullet point says that hints are used when a replica node is down already. If Cassandra will just automatically fail a write when too few replicas are alive, what's the point of storing hints for a write that has already been deemed a failure?</p>