php把session存储在数据库性能如何啊？

Question

SessionHandler.php文件内容如下

<?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文件内容如下

<?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表结构如下

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;

Answer 1

不推荐存数据库中，假如站点访问量大的时候，对数据库会频繁写入,频繁读取，从而影响数据库性能。一般用redis memcache存更好些。而且维护过期时间等也方便。设置key过期时间就好。

Answer 2

存redis这些缓存应用就可以了，读取高效，自动过期