优化使用mysql存储session

  之前写过两篇文章《自定义SESSION(二)——数据库保存》和《我为什么不使用session》
   但后来发现都有问题。前者处理在实际中几乎没什么用处,而且session回收还得自己另外处理。后者频繁的操作数据库,打来了很大的性能问题。
   这两天仔细考虑下,大致给出一个方案,但还没有具体详细的测试。
   1、session处理和统计结合起来。同时游客也都有记录。
   2、完全使用数据库和cookie来模拟session的功能。
   3、用户的对session的操作都尽量保证在一条sql语句完成。不用到session的时候,绝对不多一条查询。
   4、为了效率起见,session的回收没有集成进来,但提供了接口,可以调用实现。
  暂时给出代码,不具体解释。
  sql
  CREATE TABLE `*****_session` (
  `sid` char(32) NOT NULL,
  `uid` int(10) NOT NULL,
  `username` char(32) NOT NULL,
  `usertype` tinyint(1) NOT NULL,
  `activetime` int(10) NOT NULL,
  `expiry` int(10) NOT NULL,
  `ip` char(15) NOT NULL,
  `url` char(80) NOT NULL,
  `value` char(255) NOT NULL,
  PRIMARY KEY (`sid`)
  ) ENGINE=MEMORY DEFAULT CHARSET=utf8;
  php代码
  <?
  class session{
  
   private $_sessionPrex= '';//session的前缀
  
   private $_time = '';//当前时间
  
   private $_model = null;//数据库操作模型
  
   private $_expiry = 1200;//session有效时间
  
   private $_domain = '';//session的作用域
  
   protected $isNew = 0;//判定操作动作 0 更新 1 增加
  
   protected $session = array();//对应的一条session记录
  
   public function __construct($options){
   $this->_setOptions($options);
   if(empty($this->_time))$this->_time = time();
   $this->session['activetime'] = $this->_time;
   }
  
   public function start(){
   $this->_getSid();
   }
  
   public function set($key,$value){
   if(in_array($key,array('uid','username','usertype','url','expiry'))){
   if($key == 'expiry'){
   $this->_setCookie($this->_sessionPrex.'_sid',$this->session['sid'],$value);
   $this->_setCookie($this->_sessionPrex.'_uid',$this->session['uid'],$value);
   }
   $this->session[$key] = $value;
   }else{
   $other = $this->session['value'];
   $other[$key] = $value;
   $this->session['value'] = $other;
   }
   }
  
   public function get($key){
   if(in_array($key,array('uid','username','usertype','url','expiry'))){
   return $this->session[$key];
   }else{
   if(isset($this->session['value'][$key])){
   return $this->session['value'][$key];
   }
   return null;
   }
   }
  
   public function gc($file,$time = 1200){
   $lasttime = file_get_contents($file);
   if($lasttime + $time<$this->_time){
   file_put_contents($file,$this->_time);
   return $this->_model->delete('activetime+expiry<'.$this->_time);
   }
   }
  
   public function destroy(){
   $this->session['uid'] = 0;
   $this->session['username'] = '';
   $this->session['usertype'] = -1;
   $this->session['expiry'] = $this->_expiry;
   $this->session['value'] = array();
   $this->_setCookie($this->_sessionPrex.'_sid',$this->session['sid'],$this->_expiry);
   $this->_setCookie($this->_sessionPrex.'_uid',$this->session['uid'],$this->_expiry);
   }
  
   public function __destruct(){
   $this->_save();
   }
  
   private function _save(){
   $dbSession = $this->session;
   $dbSession['value'] = serialize($dbSession['value']);
   if(strlen($dbSession['value'])>255)$this->_error('session->value is too long!');
   if($this->isNew == 1){
   //增加
   $this->_model->insert($dbSession);
   }else{
   //更新
   $sid = $dbSession['sid'];
   $this->_model->update(array_slice($dbSession,1),'sid=\''.$sid.'\'');
   }
   }
  
   private function _getSession($sid){
   $dbSession = $this->_model->detail('sid = \''.$sid.'\'');
   if(!$dbSession)return false;
   $dbSession['value'] = unserialize($dbSession['value']);
   $this->session = array_merge($dbSession,$this->session);
   return true;
   }
  
   private function _getSid(){
   $sid = strip_tags($_COOKIE[$this->_sessionPrex.'_sid']);
   if(strlen($sid)==32){
   if($this->_getSession($sid)){
   return true;
   }
   }else{
   $sid = md5(time().mt_rand(1000,10000));
   $this->_setCookie($this->_sessionPrex.'_sid',$sid);
   }
   $this->_setCookie($this->_sessionPrex.'_uid',0);
   $this->session = array(
   'uid' => 0,
   'username' => '',
   'usertype' => -1,
   'activetime' => $this->_time,
   'ip' => $this->_getip(),
   'url' => strip_tags($_SERVER['REQUEST_URI']),
   'expiry' =>$this->_expiry,
   'value' => array()
   );
   $this->isNew = 1;
   $this->session['sid'] = $sid;
   }
  
   private function _setCookie($name,$value,$expiry=0){
   if(empty($expiry))$expiry = $this->_expiry;
   if(empty($this->_domain)){
   setcookie($name,$value,$this->_time + $expiry,'/');
   }else{
   setcookie($name,$value,$this->_time + $expiry,'/',$this->_domain);
   }
   }
  
   private function _getip(){
   return getip();
   }
  
   private function _setOptions($options){
   foreach ($options as $key=>$value){
   if(in_array($key,array('sessionPrex','time','model','expiry','domain'))){
   $key = '_'.$key;
   $this->$key = $value;
   }
   }
   }
  
   private function _error($msg){
   throw new Phpbean_Exception($msg);
   }
  }
  ?>
  (注意,该代码不能直接使用,本文主要是提供一种思路)