public T getUpdateIfChanged(String agentHash) throws AmbariException {
    initializeDataIfNeeded(true);
    return !Objects.equals(agentHash, data.getHash()) ? data : getEmptyData();
  }
Is used to saving and updating last version of event in cluster scope
@param <T> event with hash to control version
ambari-server/src/main/java/org/apache/ambari/server/agent/stomp/AgentClusterDataHolder.java