@Override
  public String toString() {
    return getClass().getSimpleName() + " [requestId=" + requestId + "]";
  }
RequestId identifies the HeartbeatRequestMessage for which this is a response. If it is < 0
this is a periodic heartbeat message.
geode-membership/src/main/java/org/apache/geode/distributed/internal/membership/gms/messages/HeartbeatMessage.java