public static function getDbNo($identifier)
 {
     $sign = $identifier;
     is_numeric($identifier) || ($sign = Sign::sign64($identifier));
     $tag = intval(Sign::mod($sign, AppConf::$dbConf['db_num'] * AppConf::$dbConf['tb_num']) / AppConf::$dbConf['tb_num']);
     return $tag;
 }