protected function getStorageKey($key, $limit, $milliseconds)
    {
        $window = $milliseconds * (floor((microtime(1) * 1000)/$milliseconds));
        $date = date('YmdHis', $window/1000);
        return $date . '::' . $key . '::' . $limit . '::' . $milliseconds . '::COUNT'; 
    }