SessionHandler.php the contents of the file are as follows

<?php
namespace Dry\Base;

class SessionHandler{

    private $pdo = null;

    private $lifeTime = 1440;

    public function __construct($pdo)
    {
        $this->pdo = $pdo;
        $this->lifeTime = get_cfg_var("session.gc_maxlifetime");
        session_set_save_handler(
            array($this, "open"),
            array($this, "close"),
            array($this, "read"),
            array($this, "write"),
            array($this, "destroy"),
            array($this, "gc")
        );
        register_shutdown_function("session_write_close");
    }

    public function open($save_path, $session_name)
    {
        return true;
    }

    public function close()
    {
        return true;
    }

    public function read($session_id)
    {
        $time = date("Y-m-d H:i:s");
        $sql = "select session_data from session_handler where session_id="{$session_id}" and session_expires>"{$time}" limit 1";
        $sm = $this->pdo->prepare($sql);
        $sm->execute();
        if($sm->rowCount()){
            $result = $sm->fetch();
            return $result["session_data"];
        }
        else{
            return "";
        }
    }

    public function write($session_id, $session_data)
    {
        $time = date("Y-m-d H:i:s", time()+$this->lifeTime);
        $sql = "select count(1) as total from session_handler where session_id="{$session_id}" limit 1";
        $sm = $this->pdo->prepare($sql);
        $sm->execute();
        if($sm->fetchColumn()){
            $sql="update session_handler set session_data="{$session_data}",session_expires="{$time}" where session_id="{$session_id}"";
        }
        else{
            $sql="insert into session_handler(session_id,session_data,session_expires) values("{$session_id}","{$session_data}","{$time}")";
        }
        $sm = $this->pdo->prepare($sql);
        $sm->execute();
        return true;
    }

    public function destroy($session_id)
    {
        $sql = "delete from session_handler where session_id="{$session_id}"";
        $sm = $this->pdo->prepare($sql);
        $sm->execute();
        return true;
    }

    public function gc($maxlifetime)
    {
        $time = date("Y-m-d H:i:s", time()-$maxlifetime);
        $sql = "delete from session_handler where session_expires<"{$time}"";
        $sm = $this->pdo->prepare($sql);
        $sm->execute();
        return true;
    }

}
?>

test.php the contents of the file are as follows

<?php
require_once("SessionHandler.php");

use Dry\Base\SessionHandler;

$pdo = new PDO("mysql:host=192.168.1.20;dbname=test;port=3306", "root", "1234", array(
    PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
    PDO::ATTR_PERSISTENT => false,
    PDO::MYSQL_ATTR_INIT_COMMAND => "set names utf8",
    PDO::ATTR_ORACLE_NULLS => PDO::NULL_TO_STRING,
    PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC
));

new SessionHandler($pdo);
session_start();

$_SESSION["name"] = "test";
echo $_SESSION["name"];
?>

session_handler the structure of the table is as follows

CREATE TABLE `session_handler` (
  `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
  `session_id` varchar(64) NOT NULL,
  `session_data` mediumtext,
  `session_expires` datetime NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `session_id` (`session_id`) USING BTREE
) ENGINE=InnoDB AUTO_INCREMENT=1 DEFAULT CHARSET=utf8;