best way to use cache system in our app

We have an Android App with large number of users (about 300K) with lot of requests and calculations using Yii Framework as web-service.

we have a function named getUserRank that takes user_id & timePeriod to calculate the user rank according to 3 tables (using huge joins) and we use it in our app a lot for every single user.


 * get user rank of the user according to the specified period

 * periods: 0-> all  1-> daily  2-> weekly 3-> monthly


public function getUserRank($user_id, $timePeriod){

// piece of code


I use Xcache and mod_php on my server. Is this a good job to store all of the user ranks for few hours before requesting from database in such a way (to send them by json to the App)?

$rank = Yii::app()->cache->get($user_id.$timePeriod); // generate cache id using $user_id.$timePeriod

if($rank == null){

// calculate and populate the cache variable


it depends on your setup there are many questions for instance (e.g. how often does the data change)

It is depends on me to set the expire time of each timePeriod.

My question is about this way of data caching because there are a lot of variables here to store. 4 time period for each 300k user.