详解PHP会话存储方式
; 指定会话模块是否在请求开始时自动启动一个会话。默认为 0(不启动)
; Initialize session on request startup.
; http://php.net/session.auto-start
session.auto_start = 0
在客户端，会话可以存储在cookie或者通过URL参数来获取。依赖于服务器的配置：
; 指定是否在客户端用 cookie 来存放会话 ID。默认为 1(启用)
; Whether to use cookies.
; http://php.net/session.use-cookies
session.use_cookies = 1
; 指定是否在客户端仅仅使用 cookie 来存放会话 ID。。启用此设定可以防止有关通过 URL 传递会话 ID 的攻击。
; This option forces PHP to fetch and use a cookie for storing and maintaining
; the session id. We encourage this operation as it's very helpful in combatting
; session hijacking when not specifying and managing your own session id. It is
; not the end all be all of session hijacking defense, but it's a good start.
; http://php.net/session.use-only-cookies
session.use_only_cookies = 1
如果确认存储在cookie中，则可以进一点配置会话存储在cookie中的各项配置，如cookie_name，cookie_lifetime，cookie_path，cookie_domain，cookie_secure，cookie_httponly
; Name of the session (used as cookie name).
; http://php.net/session.name
session.name = PHPSESSID
; Lifetime in seconds of cookie or, if 0, until browser is restarted.
; http://php.net/session.cookie-lifetime
session.cookie_lifetime = 0
; The path for which the cookie is valid.
; http://php.net/session.cookie-path
session.cookie_path = /
; The domain for which the cookie is valid.
; http://php.net/session.cookie-domain
session.cookie_domain =
; Whether or not to add the httpOnly flag to the cookie, which makes it inaccessible to browser scripting languages such as JavaScript.
; http://php.net/session.cookie-httponly
session.cookie_httponly =
在服务器端，同样也可以通过多种方式来存储会话。默认会话存储在文件中，此时session.save_path为创建存储文件的路径。
; Handler used to store/retrieve data.
; http://php.net/session.save-handler
session.save_handler = files
; Argument passed to save_handler. In the case of files, this is the path
; where data files are stored. Note: Windows users have to change this
; variable in order to use PHP
's session functions.
;
; The path can be defined as:
;
; session.save_path = "N;/path"
;
; where N is an integer. Instead of storing all the session files in
; /path, what this will do is use subdirectories N-levels deep, and
; store the session data in those directories. This is useful if you
; or your OS have problems with lots of files in one directory, and is
; a more efficient layout for servers that handle lots of sessions.
;
; NOTE 1: PHP will not create this directory structure automatically.
; You can use the script in the ext/session dir for that purpose.
; NOTE 2: See the section on garbage collection below if you choose to
; use subdirectories for session storage
;
; The file storage module creates files using mode 600 by default.
; You can change that by using
;
; session.save_path = "N;MODE;/path"
;
; where MODE is the octal representation of the mode. Note that this
; does not overwrite the process's umask.
; http://php.net/session.save-path
;session.save_path = "/tmp"
PHP支持通过session_set_save_handler来实现会话处理器的自定义open, close, read, write, destroy, gc处理函数，常见的会话处理器包括使用内存型分配(如mm，memcache等)，也可以使用数据库进行存储。由此可见，若需要会话存储与文件系统(例如用数据库PostgreSQL Session Save Handler或默认的文件存储files)协同工作的，此时有可能造成用户定制的会话处理器丢失了未存储数据的会话。若使用内存型分配存储，又需要考虑会话持久化存储问题。
接下来重点讲解memcache(d?)会话处理器。
Memcache模块提供了于memcached方便的面向过程及面向对象的接口，memcached是为了降低动态web应用 从数据库加载数据而产生的一种常驻进程缓存产品。
Memcache模块同时提供了一个session 处理器 (memcache).
更多关于memcached的信息请参见» http://www.memcached.org/.
memcached是一个高性能分布式的内存对象缓存系统， 通常被用于降低数据库加载压力以提高动态web应用的响应速度。
此扩展使用了libmemcached库提供的api与memcached服务端进行交互。它同样提供了一个session处理器(memcached)。 它同时提供了一个session处理器(memcached)。
关于libmemcached的更多信息可以在» http://libmemcached.org/libMemcached.html查看。
memcache会话处理器配置：
session.save_handler = memcache
session.save_path = "tcp://127.0.0.1:11211?persistent=0&weight=1&timeout=1&retry_interval=15,tcp://127.0.0.1:11212?persistent=0&weight=1&timeout=1&retry_interval=15,tcp://127.0.0.1:11213?persistent=0&weight=1&timeout=1&retry_interval=15,tcp://127.0.0.1:11214?persistent=0&weight=1&timeout=1&retry_interval=15"
数据库处理器可以使用Session PgSQL来实现(此扩展被认为已无人维护)。也可以使用其它数据库来实现会话存储，只不过需要自定义处理器函数function.session-set-save-handler.php。具体自定义处理器可参见maria at junkies dot jp。