@Override
  public final void dispose() {
    lastGroupId = null;
    PersistentHashMap<String, Long> map = recentFileTimestampMap.getValueIfInitialized();
    if (map != null) {
      try {
        map.close();
      }
      catch (IOException e) {
        LOG.info("Cannot close persistent viewed files timestamps hash map", e);
      }
    }
  }
@Override
  public final void dispose()