code: void cleanupClusterConfigFiles() throws IOException {
      Zxid latestZxid = getLatestZxid();
      List<File> files = getFilesWithPrefix(this.rootDir, "cluster_config");
      if (files.isEmpty()) {
        LOG.error("There's no cluster_config files in log directory.");
        throw new RuntimeException("There's no cluster_config files!");
      }
      Iterator<File> iter = files.iterator();
      while (iter.hasNext()) {
        File file = iter.next();
        String fileName = file.getName();
        String strZxid = fileName.substring(fileName.indexOf('.') + 1);
        Zxid zxid = Zxid.fromSimpleString(strZxid);
        if (zxid.compareTo(latestZxid) > 0) {
          // Deletes the config file if its zxid is larger than the latest zxid on
          // disk.
          file.delete();
          iter.remove();
        }
      }
      if (files.isEmpty()) {
        LOG.error("There's no cluster_config files after cleaning up.");
        throw new RuntimeException("There's no cluster_config files!");
      }
      // Persists changes.
      fsyncDirectory();
    }
docs: cluster_config files.