You want to speed up your application using a cache.
Install APC (Alternative PHP Cache)
It's easy to install with just two lines from your console.
$ sudo apt-get install -y php-apc $ sudo service apache2 restart
The first line installs the package, the second restarts apache.
APC can help your application in two ways.
First of all, is APC's opcode cache. This speeds up the execution of your program by caching the results of PHP's byte-code compiler.
Secondly, you can use APC as a cache within your application. See Setting up the APC Cache Driver for instructions on using APC as the cache driver.