session 丢失问题

1. 存到memcached中, 十分简单, 在使用session之前, 加入下面两行代码

int_set('session.save_handler', 'memcache');
int_set('session.save_path', '127.0.0.1:11211');

2.存到数据库里面, 重新定义了session的生命周期

<?php
/**
 * Class SessionDBTool
 */
class SessionDBTool{
    private $link;    //数据库连接对象
    public function __construct(){
        //自定义session处理方法
        ini_set('session.save_handler','user');
        session_set_save_handler(
            array($this,'sess_open'),
            array($this,'sess_close'),
            array($this,'sess_read'),
            array($this,'sess_write'),
            array($this,'sess_destroy'),
            array($this,'sess_gc')
        );
        //开启session
        @session_start();
    }

     //开启session
    public function sess_open(){
        $this->link = MYSQLDB::getInstance($GLOBALS['config']['database']);
        //mysql_connect('localhost','root','root');
        //mysql_query('use shop');
    }
    public function sess_close(){
        return true;
    }

    //读取session
    public function sess_read($sess_id){
        $time = time();
        $expire = ini_get('session.gc_maxlifetime');
        $sql="select sess_data from it_session where sess_id='$sess_id' and $time - time < $expire";
        if($row=$this->link->fetchRow($sql)){
            return $row['sess_data'];
        }else{
            return '';
        }
    }

    //写入session
    public function sess_write($sess_id,$sess_data){
        $expire=time();
        //存在则更新
        $sql = "replace into it_session values('$sess_id','$expire', '$sess_data')";
        return $this->link->myquery($sql);
    }

    //销毁
    public function sess_destroy($sess_id){
        $sql="delete from it_session where sess_id='$sess_id'";
        return $this->link->myquery($sql);
    }

    //垃圾回收, 可以设置概率
    public function sess_gc($ttl){
        $now = time();
        $last = $now -$ttl;
        //删除过期session
        $sql = "delete from it_session where expire < $last";
        return $this->link->myquery($sql);
    }
}