@Override
  public String toString() {
    return "ReplicaTracker: [" + remoteReplicaInfo.toString() + " " + replicaStatus.toString() + " " + throttledTill
        + "]";
  }
whenever a group is finished, this method gets called for corresponding replica trackers,
replica status is moved to unknown and replica is throttled
ambry-replication/src/main/java/com/github/ambry/replication/continuous/ReplicaTracker.java