private T initializeData(Long hostId, boolean regenerateHash) {
    T hostData;
    try {
      hostData = getCurrentData(hostId);
    } catch (AmbariException e) {
      LOG.error("Error during retrieving initial value for host: {} and class {}", hostId, getClass().getName(), e);
      throw new AmbariRuntimeException("Error during retrieving initial value for host: " + hostId + " and class: " + getClass().getName(), e);
    }
    if (regenerateHash) {
      regenerateDataIdentifiers(hostData);
    }
    return hostData;
  }
Is used to saving and updating last version of event in host scope
@param <T> event with hash to control version
ambari-server/src/main/java/org/apache/ambari/server/agent/stomp/AgentHostDataHolder.java