可能很多PHPer都用到了PHP提供的Session功能，可以方便的进行会话功能处理，PHP服务端默认的session存储是文件存放方式，在Windows上PHP默认的Session服务端文件存放在C:\WINDOWS\Temp下，*NIX下默认存放在/tmp下，如果说并发访问很大或者session建立太多，在这两个目录下就会存在大量类似sess_xxxxxx的session文件，同一个目录下文件数过多会导致性能下降，并且可能导致受到攻击最终出现文件系统错误。针对这样的情况，PHP本身体提供了比较好的解决办法。
不少朋友可能都没有注意到php.ini里面Session设置部分中有这样一项：
这项设置提供给我们可以给session存放目录进行多级散列，其中“N”表示要设置的目录级数，“MODE”表示目录的权限属性，默认为600，在WINDOWS上基本是不用设置的，*NIX上也可以不用设置，后面的“/path”表示session文件存放的根目录路径，比如我们设置为下面的格式
上面的设置表示我们把/tmp/phpsession目录作为php的session文件存放根目录，在该目录下进行两级目录散列，每一级目录分别是0-9和a-z共36个字母数字为目录名，这样存放session的目录可以达到36*36个，相信作为单台服务器来说，这是完全够用了，如果说您的系统架构设计为多台服务器共享session数据，可以把目录级增加到3级或者更多。
需要注意的是，php自己并不会自动创建子目录，需要您自己动手去创建，网上找到这样的自动创建目录的代码，大家可以做个参考。下面的代码自动创建3级子目录，可以自己动手根据需要进行修改。
set_time_limit(0);
$string = '0123456789abcdefghijklmnopqrstuvwxyz';
$length = strlen($string);
function makeDir($param)
{
if(!file_exists($param)) {
makeDir(dirname($param));
mkdir($param);
}
}
for($i = 0; $i < $length; $i++) {
for($j = 0; $j < $length; $j++) {
for($k = 0; $k < $length; $k++) {
makeDir($string[$i].'/'.$string[$j].'/'.$string[$k]);
}
}
}
?>
大家可能注意到前面的文字中提到了有关多服务器共享php的SESSION，这是很多应用都会遇到的问题，网上也有不少相关的资源，大家可以去google一下，Michael这里只提一下大概的思路。
一般来说我们用到最多的方法有两种：
1、NFS或者Samba共享的方法，让各个服务器上存放session文件的磁盘共享，这种方法简单可行。
2、集中存储到数据库中，这是比较多的实现方法，通过php提供的session_set_save_handler()函数来重定义session函数，推荐使用这种方法。
欢迎大家一起交流和讨论php中和session相关的技巧和经验。
不错，以前就注意到这个功能，不过一直没试过，现在正好一试:)
另外，关于session，我遇到了一个调试了几乎一个下午也没解决的问题，不知Michael有没有遇到过，简单地说就是下面的三段代码：
index.php:
diogin.php:
another.php:
这样，访问index.php，将新建一个session，然后删除，再检查cookie数组。这三段代码是能正常工作的，可以把session使用的cookie删除。但当我把类似的代码集成进系统后，想用setcookie来删除会话cookie，就行不通，调试了一下午都没解决。不知这里是不是有什么需要注意的事情我没察觉到，Michael遇到过类似的情况吗？
啊，奇怪，源代码怎么给过滤掉了？
那再发一次，不好意思:)
index.php:
session_save_path(‘./’);
session_name(‘DIOGIN_SESSID’);
session_start();
$_SESSION[‘diogin’] = ‘haha’;
header(‘Location: diogin.php’);
diogin.php:
session_save_path(‘./’);
session_name(‘DIOGIN_SESSID’);
if (isset($_COOKIE[‘DIOGIN_SESSID’])) {
session_start();
$_SESSION = array();
session_destroy();
setcookie(‘DIOGIN_SESSID’, false);
header(‘Location: another.php’);
}
another.php:
var_dump($_COOKIE);
说实话，我仔细看了您的留言，但是我还没有搞明白你到底想实现的需求和功能，从你的代码来看，很少看到这样使用cookie和session的，不知道是为了满足什么需求，通常来说，session在我们的应用里面，迫不得已才使用，比如验证码图片，别的地方如果要使用到session，我们都是使用自己开发的session管理，session存储在内存数据库中。
如有可能，你可以再把要实现的需求整理一下告知。
有一个将 PHP Session 利用 memcached 来保存的类。好像是一个丹麦的人写的。 🙂
[Comment ID #13354 Will Be Quoted Here]
这位朋友说得很对，我用数据库保存过，为了多台机器共享session，用memcached原理一样，就是存储和读取的时候把从数据库改成从memcached操作，另外还可以使用共享内存，比如PHP的APC扩展。
我 PHP.INI 知道有这个设置。但真不知道可以设置散列目录储存。
一般我用session_save_path 不过好象这个函数并不支持目录散列。呵呵
[Comment ID #25801 Will Be Quoted Here]
最新的pecl_memcached 扩展可以支持直接在php.ini里面设置类似这样的东西：
session.save_handler = memcache
session.save_path = “tcp://host:port?persistent=1&weight=2&timeout=2&retry_interval=15,tcp://host2:port2”
比如设置：session.save_path = “tcp://127.0.0.1:11211″， 连接本机上11211端口的memcached来存储session
详细的语法可以参考官方文档 php_memcache.h cvs log
最新的session共享和性能提升将使用memcached来存储session，见php.ini的文档部分就明白了，可以设置多个memcached给php的session来使用，并且可以配置各个mc的权重，这是我们现在主流的使用手段。
你好！ 我想问一下 我用了 session_save_path 更改了session保存路径 后来发现我生成的sesion文件夹一直都没有删除过。 就是生成一个之后这一个文件一直都会在。请问这种 情况是什么 原因呢
这个问题是这样的，php的session有自动回收机制，通过session.cookie_lifetime，session.gc_probability，session.gc_divisor以及session.gc_maxlifetime几个参数来控制，在满足条件的情况下，系统会自动进行垃圾回收，但是有一种情况，如果你在session.save_path选项中设定使用子目录来存储session数据文件，垃圾回收程序不会自动启动，你必须使用自己编写的shell脚本、cron项或者其他办法来执行垃圾文件处理。
如我前面所说的，现在普遍采用的办法已经不是使用多集目录的方式来存储session文件，而是采用更高效的memcached或者redis等内存缓存来实现，建议你研究研究，在机器上配置一个memcached，很简单的，这样一劳永逸，还可以实现分布式的服务器之间共享session
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