@Override
  public String toString() {
    return "Event #" + getSeqid() + " of type " + eventType + " (" + getInformativeName() + ")";
  }
Default prioritized runnable comparator which implements a FIFO ordering.
<p>
Subclasses should not override this. Instead, if they want to implement priority beyond FIFO,
they should override {@link #getPriority()}.
hbase-server/src/main/java/org/apache/hadoop/hbase/executor/EventHandler.java