Martin Fjordvald

This is part two in my caching series. Part one covered the concept behind the full page caching as well as potential problems to keep in mind. This part will focus on implementing the concept in actual PHP code. By the end of this you’ll have a working implementation that can cache full pages and invalidate them intelligently when an update happens.

Requirements

I’ll provide a fully functional framework with the simple application I used to get my benchmark figures. You’ll need the following software to be able to run it.

• Nginx. I’m not sure which exact version but I generally use and recommend the latest development version.
• PHP 5.3.0. I recommend at least 5.3.3 so you’ll have PHP-FPM for your fastcgi process management.
• MySQL
• Memcached

The Framework

I’ll be referencing the code on github instead of pasting it in this post to keep the size down, so you will probably want to download it.

Edit: Part 2 is now available.

This is the first entry in a short series I’ll do on caching in PHP. During this series I’ll explore some of the options that exist when caching PHP code and provide a unique (I think) solution that I feel works well to gain high performance without sacrificing real-time data.

Caching in PHP is usually done on a per-object basis, people will cache a query or some CPU intensive calculations to prevent redoing these CPU intensive operations. This can get you a long way. I have an old site which uses this method and gets 105 requests per second on really old hardware.

An alternative that is used, for example in the Super Cache WordPress plug-in, is to cache the full-page data. This essentially mean that you create a page only once. This introduces the problem of stale data which people usually solve by checking whether data is still valid or by using a TTL caching mechanism and accepting stale data.

The method I propose is a spin on full-page caching. I’m a big fan of nginx and I tend to use it to solve a lot of my problems, this case is no exception. Nginx has a built-in Memcached module, with this we can store a page in Memcached and have nginx serve it – thus never touching PHP at all. This essentially turns this: