public AlertHistoryEntity merge(AlertHistoryEntity alert) {
    if (m_configuration.isAlertCacheEnabled()) {
      synchronized (this) {
        return mergeTransactional(alert);
      }
    } else {
      return mergeTransactional(alert);
    }
  }
Merge the speicified alert with the existing alert in the database.

@param alert
         the alert to merge (not {@code null}).
@return the updated alert with merged content (never {@code null}).
ambari-server/src/main/java/org/apache/ambari/server/orm/dao/AlertsDAO.java