session写入数据库

<?php
    class session
    {
        private static $handle = null;
        private static $ip = null;
        private static $lifetime = null;
        private static $time = null;
        
        static function init($pdo)
        {
            self::$handle = $pdo;
            self::$ip = !empty($_SERVER["REMOTE_ADDR"]) ? $_SERVER["REMOTE_ADDR"] : "unknow";
            self::$lifetime = ini_get('session.gc_maxlifetime');
            self::$time = time();
        }

        static function start($pdo)
        {
            self::init($pdo);
            session_set_save_handler(
                array(__CLASS__,'open'),
                array(__CLASS__,'close'),
                array(__CLASS__,'read'),
                array(__CLASS__,'write'),
                array(__CLASS__,'destroy'),
                array(__CLASS__,'gc')
            );
            session_start();
        }

        public static function open($path, $name)
        {
            return true;
        }

        public static function close()
        {
            return true;
        }

        public static function read($PHPSESSID)
        {
            $sql = "select * from session where PHPSESSID = ?";
            $smit = self::$handle->prepare($sql);
            $smit->execute(array($PHPSESSID));

            if(!$result = $smit->fetch(PDO::FETCH_ASSOC))
            {
                return '';
            }

            if(self::$ip != $result['client_ip'])
            {
                self::destroy($PHPSESSID);
                return '';
            }

            if( ($result['update_time'] + self::$lifetime) < self::$time)
            {
                self::destroy($PHPSESSID);
                return '';
            }

            return $result['data'];
        }

        public static function write($PHPSESSID,$data)
        {
            $sql = "select * from session where PHPSESSID = ?";
            $stmt = self::$handle->prepare($sql);
            $stmt->execute(array($PHPSESSID));

            if($result = $stmt->fetch(PDO::FETCH_ASSOC))
            {
                if($result['data'] != $data || self::$time-30 > $result['update_time'])
                {
                    $sql="update session set update_time = ?, data =? where PHPSESSID = ?";
                    $stmt = self::$handle->prepare($sql);
                    $stmt->execute(array(self::$time,$data,$PHPSESSID));
                }

                
            }else
            {
                if(!empty($data))
                {
                    $sql="insert into session(PHPSESSID, update_time, client_ip, data) values(?,?,?,?)";
                    $sth = self::$handle->prepare($sql);
                    $sth->execute(array($PHPSESSID,self::$time,self::$ip,$data));
                }
            }
            return true;
        }

        public static function destroy($PHPSESSID)
        {
            $sql = "delete from session where PHPSESSID = ?";
            $sth = self::$handle->prepare($sql);
            $sth->execute(array($PHPSESSID));
            return true;
        }

        public static function gc($lifetime)
        {
            $sql = "delete from session where update_time < ?";
            $stmt=self::$handler->prepare($sql);
            $stmt->execute(array(self::$time-self::$lifetime));
            return true;
        }
    }
    
    try{
        $pdo = new PDO("mysql:host=localhost;dbname=test", "root" ,"");
    }catch(PDOException $e)
    {
        echo $e->getMessage();
    }

    session::start($pdo);