@Override
    public long read(int fileId,
                     long defaultValue) throws IOException {
      if (defaultValue != 0) {
        throw new UnsupportedOperationException(
          "defaultValue=" + defaultValue + ": so far only 0 is supported default value for fast-attributes");
      }
      return helper.readLongField(fileId, FIELD_OFFSET);
    }
@Override
    public long read(int fileId,
                     long defaultValue)