What is faster? File_exist or MySQL query?

Question

Users in my webgame are having certain player information cached in the $_SESSION of PHP. Each time they load the game it checks if the session exists, if not they get the player information from a MySQL database and then it gets stored in the $_SESSION.

Now my problem is, what if the player information gets updated by another process or player? They can't update the $_SESSION cache of the other player.

I know memcached is most probably the solution for this, but I'm not sure if I should take the time for something like this. $_SESSION cache is doing well for me, except for this.

• I was thinking about creating a MySQL table for it which get read at every request and if there's a record for the player that it recreates the cache.
• One other solution would be to create a file in a directory with the id of the player in the name of the file. Every request PHP will check with file_exist if it should clear the cache or not.

What would you guys do? It gets executed every request so it's pretty important to get this optimized.

Answer 1

From a design standpoint alone I'd avoid the file_exists and directory approach. Sure 'file_exists' is fast, but it won't scale well... What happens if a use changes their name?

If you're using APC (and you should) you could APC's user memory cache. As long as you're on a single server it should give you similar performance benifits as memcached without the need for a separate memory caching server process. If a user entry changes frequently, you could run into fragmemntation issues with APC though. In that case, time to bite the bullet and go with memcached--you can even store your session data in memcached for a performance boost.

Also, neither APC or your file_exists solution will scale to multiple load balanced servers--you'd need a DB solution or memcached for that.