public function commit($expungeDeletes = false, $waitFlush = null, $waitSearcher = true, $timeout = 3600)
    {
        if ($waitFlush) {
            user_error('waitFlush must be false when using Solr 4.0+' . E_USER_ERROR);
        }

        $expungeValue = $expungeDeletes ? 'true' : 'false';
        $searcherValue = $waitSearcher ? 'true' : 'false';

        $rawPost = '<commit expungeDeletes="' . $expungeValue . '" waitSearcher="' . $searcherValue . '" />';
        return $this->_sendRawPost($this->_updateUrl, $rawPost, $timeout);
    }