Are there problems using PHP sessions in a server cluster?

We are developing 开发者_JAVA百科a web site in PHP, and we have to use sessions. The site will be published in a server cluster. How can we make that work?

Thanks.

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Yes this is possible, you need to store your sessions in a central location like a database though. This is pretty simple and just requires you to make some changes to session_set_save_handler - there's a good example of the process you need to follow here

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I would use memcache to store your sessions. It will be much faster than storing them in a database or disk.

Database storage is good but you will need more databases when your site becomes very high traffic. Sessions on disk will also cause a lot of IO issues when your site gets a lot of traffic. Memcache on the other hand scales much better than a DB and files.

I personally use memecache and the sites i work on get millions of hits a day. I have never had any issues with storing sessions in memcache.

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If you've got multiple PHP boxes, you'll want a central session store.

Your best choices are probably database (that link from seengee's answer is a good explanation) or a dedicated memcache box.

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A shared NFS mount for the session directory would be an option, though I've always found nfs performance a bit slow. Alternatives are to write your own session handler using memcache or database for the sessions.

An alternative option is to load balance your web servers using sticky sessions, which will ensure that requests from the same client always go to the same server during the course of the session.