private function _loadDelFile()
    {
        if ($this->_delGen == -1) {
            // There is no delete file for this segment
            return null;
        } else if ($this->_delGen == 0) {
            // It's a segment with pre-2.1 format delete file
            // Try to load deletions file
            return $this->_loadPre21DelFile();
        } else {
            // It's 2.1+ format deleteions file
            return $this->_load21DelFile();
        }
    }