@Subscribe
  @Transactional
  public void onHostEvent(HostsRemovedEvent event) {
    if (LOG.isDebugEnabled()) {
      LOG.debug(event.toString());
    }
  }
Host repo_version entities are removed via cascade.

@param event
         the removal event.
ambari-server/src/main/java/org/apache/ambari/server/events/listeners/upgrade/HostVersionOutOfSyncListener.java