code: @Deprecated
    private DatanodeDescriptor getDatanodeByIndex(int index) {
      int i = 0;
      for (DatanodeDescriptor node : datanodeMap.values()) {
        if (i == index) {
          return node;
        }
        i++;
      }
      return null;
    }
docs: Stop at and return the datanode at index (used for content browsing)