public function markUrlAsFollowed(PHPCrawlerURLDescriptor $UrlDescriptor)
  {
    PHPCrawlerBenchmark::start("marking_url_as_followes");
    $hash = md5($UrlDescriptor->url_rebuild);
    $this->PDO->exec("UPDATE urls SET processed = 1, in_process = 0 WHERE distinct_hash = '".$hash."';");
    PHPCrawlerBenchmark::stop("marking_url_as_followes"); 
  }