@Override
  public int getPriority(RequestHeader header, Message param, User user) {
    int priorityByAnnotation = getAnnotatedPriority(header);

    if (priorityByAnnotation >= 0) {
      return priorityByAnnotation;
    }
    if (param == null) {
      return HConstants.NORMAL_QOS;
    }
    return getBasePriority(header, param);
  }
Returns a 'priority' based on the request type.
<p/>
Currently the returned priority is used for queue selection.
<p/>
See the {@code SimpleRpcScheduler} as example. It maintains a queue per 'priority type':
<ul>
<li>HIGH_QOS (meta requests)</li>
<li>REPLICATION_QOS (replication requests)</li>
<li>NORMAL_QOS (user requests).</li>
</ul>
hbase-server/src/main/java/org/apache/hadoop/hbase/ipc/AnnotationReadingPriorityFunction.java