php session writes to database

<?php
 
#
#   codeMaker Alpha 0.1.1 ( haowei.me )
#   This framework comply with the GPL license agreement
#
 
class session_handler {
     
    protected $maxlifetime = null;
    protected $dbHandle = null;
    public $config = null;
     
    public static function init($args) {
        return new self($args);
    }
     
    public function __construct($args) {
         
        $this->config = $args;
        $this->maxlifetime = get_cfg_var("session.gc_maxlifetime");
        session_set_save_handler(
        array($this, "open"),
        array($this, "close"),
        array($this, "read"),
        array($this, "write"),
        array($this, "destroy"),
        array($this, "gc"));
         
    }
     
    public function open() {
        $this->link = mysqli_connect(
        $this->config[&#39;host&#39;], 
        $this->config[&#39;user&#39;], 
        $this->config[&#39;password&#39;], 
        $this->config[&#39;database&#39;]);
        mysqli_set_charset($this->link, "utf8");
        $sql = &#39;CREATE TABLE IF NOT EXISTS `%s` (
        `session_id` varchar(255) NOT NULL,
        `session_data` text,
        `session_expires` char(10) NOT NULL,
        PRIMARY KEY (`session_id`)
        ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;&#39;;
        $sql = sprintf($sql, $this->config[&#39;table&#39;]);
        mysqli_query($this->link, $sql);
        return true;
    }
     
    public function close() {
        return true;
    }
     
     
    public function read($session_id) {
        if(empty($session_id)) return null;
         
        $sql = &#39;SELECT `session_data` AS `data` FROM `%s` WHERE `session_id` = "%s" AND `session_expires` > "%u"&#39;;
        $sql = sprintf($sql, 
        mysqli_real_escape_string($this->link, $this->config[&#39;table&#39;]), 
        mysqli_real_escape_string($this->link, $session_id),
        time());
         
        $result = mysqli_query($this->link, $sql);
        $row = mysqli_fetch_assoc($result);
        return $row[&#39;data&#39;];
         
    }
     
    public function write($session_id, $session_data) {
        if(empty($session_id)) return null;
         
        $newExpires = time() + $this->maxlifetime;
        $sql = &#39;REPLACE INTO `%s` SET `session_id` = "%s", `session_data` = "%s", `session_expires` = "%u"&#39;;
        $sql = sprintf($sql, 
        mysqli_real_escape_string($this->link, $this->config[&#39;table&#39;]), 
        mysqli_real_escape_string($this->link, $session_id),
        mysqli_real_escape_string($this->link, $session_data),
        $newExpires);
         
        $result = mysqli_query($this->link, $sql);
        return mysqli_affected_rows($this->link);
         
    }
     
    public function destroy($session_id) {
        $sql = &#39;DELETE FROM `%s` WHERE `session_id` = "%s"&#39;;
        $sql = sprintf($sql, 
        mysqli_real_escape_string($this->link, $this->config[&#39;table&#39;]), 
        mysqli_real_escape_string($this->link, $session_id));
 
        $result = mysqli_query($this->link, $sql);
        return mysqli_affected_rows($this->link);
    }
     
    public function gc() {
        $sql = &#39;DELETE FROM `%s` WHERE `session_expires` < "%u"&#39;;
        $sql = sprintf($sql, 
        mysqli_real_escape_string($this->link, $this->config[&#39;table&#39;]), 
        time());
         
        $result = mysqli_query($this->link, $sql);
        return mysqli_affected_rows($this->link);
    }
     
}
 
class session {
 
    public static $collection = null;
     
    public static function open($clean = false, $token = false) {
        if($clean) ob_end_clean();
        if($token) session_id($token);
        session_start();
        self::$collection = $_SESSION;
    }
     
    public static function id() {
        $num_args = func_num_args();
        if($num_args) {
            $args = func_get_arg(0);
            return session_id($args);
        }else{
            return session_id();
        }
    }
     
    public static function get($name) {
        return isset($_SESSION[$name]) ? $_SESSION[$name] : null;
    }
     
    public static function set($name, $value) {
        $_SESSION[$name] = $value;
        return true;
    }
     
    public static function delete($name) {
        if(!isset($_SESSION[$name])) return null;
        unset($_SESSION[$name]);
        return true;
    }
     
    public static function destroy() {
        session_destroy();
    }
     
}
 
 
 
$config = array(
"host"=> "127.0.0.1",
"user"=> "root",
"password"=> "123456",
"database"=> "test",
"charset"=> "utf8",
"table"=> "user_session");
 
session_handler::init($config);
session::open();
session::set("profile", array("id"=> 1, "user"=> "haowei", "vip-level"=> 6));