This weekend I sat down and tackled the RAM problem: the amount of memory it takes the server to generate a single page of a website.

For Backboard, we have our server set up to allocate just 16 MB of RAM to PHP for the execution of each request. This allows us maximize the number of Apache processes we can run on a single server and thus maximize the number of users we support. To do this, though, means that the site has to be pretty light on its memory requirements.

Backboard, as a CakePHP application, has a theoretical minimum requirement for RAM: namely, the amount needed to execute a base installation of Cake. In our testing, this falls between 4 and 6 MB. The goal, of course, is to minimize anything above and beyond this.

Here are some concrete steps you can take to limit the RAM needs of your site:

1. Install a PHP opcode cache, such as eAccelerator, APC, or Xcache.
This prevents the server from having to recompile your PHP scripts on every request, a process that is both RAM- and CPU-intensive. The three options I’ve listed are relatively interchangeable and relatively comparable in terms of performance gains. We went with the first one. eAccelerator took just a few minutes to install and required no code changes, so it is time well spent!

2. Use CakePHP Components wisely.
In Cake, Components are relatively heavy - they add a fair bit of processing overhead and memory use to your application. They definitely have their place, but take care to include only the ones you really need, since they are loaded on every request.

3. Load CakePHP Vendor files lazily.
Cake has great support for vendor code - that is, 3rd party libraries that you call from your application to avoid re-implementing the wheel. Be wary, however, of calling App::import(’Vendor’, …); at the top of any of your controllers or components. What this does is load the vendor libraries for every page on your site, even if that code is not used! Instead, place your App::import() statement immediately before you use the library. That way, it is only loaded if you actually make the call!

4. Controllers are the answer!
The best way to minimize the amount of RAM a given request requires is to separate your actions into multiple controllers, based on what components, models, and helpers they require. This is always a good idea for clarity of code, but with Cake it is beneficial to take it a step further if speed and memory are a concern.

To provide a concrete example, let’s say you want the home page of your site to be as fast as possible. (Sounds reasonable, right?) If the page is not entirely static content, it has to go through a controller, so the optimal technique is to place it in its own controller and only include the components that it needs. By so doing, you eliminate all unnecessary code from the request. Now, it would be ridiculous to place every action in its own controller, but it should be pretty easy to group your actions into a few smaller clusters.

Hopefully these tips provide a launching point for your optimization efforts. What other tricks have you discovered?