PHP counts online users

/**
 * Created by PhpStorm.
 * User: jifei
 * Date: 15/11/24
 * Time: 20:58
 *
 * Millions of users per minute, real-time statistics of the total number of online users in the last 15 minutes
*/
class OnlineUser
{
 public $prefix_key = "online";//key prefix
 public function __construct()
 {
 $this->redis = new Redis();
 }
 /**
 * Add new online users to the collection
 *
 * @param $uid
*/
 public function addUser($uid)
 {
 $this->redis->sAdd($this->prefix_key . date('hi '), $uid);
 }
 /**
 * Get the number of online users
 *
 * @param $start_min Statistics start minute hi format
 * @param $end_min Statistics end minutes
 *
 * @return mixed
*/
 public function userNum($start_min, $end_min)
 {
 //The first parameter, the key name of the union
 $params[] = $this->prefix_key . $start_min . '_' . $end_min;
 //Traverse all the minutes in the time interval and put them into the parameters
 for ($min = $start_min; $min < $end_min; $min++) {
 $params[] = $this->prefix_key . $min;
 }
 //Find the union of all minute users and save it. The performance is much faster than direct calculation and return, eliminating the need for data transmission
 $num = call_user_func_array([$this->redis, "sUnionStore"], $params);
 //Delete the temporary union
 $this->redis->delete($params[0]);
 return $num;
 }
}

PHP