使用缓存系统进行会话存储？

Question

Say I have a caching system that i can use for storing sessions:

// example i have a cache class
$memcached->add('key','value');
// then i can get the session from
$memcached->get('key');

What are the advantages and disadvantages of using caching (e.g. memcached, maybe Redis can fit in, or other things) for sessions rather than using PHP's built-in sessions?

Answer 1

You should be able to have PHP store session data in Apache's runtime memory by setting session.save_handler to mm. However, to do this you need to compile PHP with the memory management module (--with-mm), which I don't think is available for Windows.

If you want to use memcached or some other caching mechanism, then it'd probably be best to implement user-defined storage handlers using session_set_save_handler so you don't have to rewrite your session management code.

If you do that, then I don't think there are any obvious disadvantages to storing session data in that way. The obvious advantage is speed.

Edit: I came across this page which discusses, aside from speed, the main advantages/disadvantages of using memcached for storing sessions, namely:

• It's easy to share sessions across multiple webservers without using sticky sessions.
• However, memcached makes no promises of keeping the data up until expiration—only that the data will not be available after expiration. So if memcached is low on ram, hasn't been used lately, or the server goes down at all, the session data will be lost.