PHP Performance Profiling
Due to the incredible growth of PHP in the last couple of years, it's now being used for tasks ranging from tiny scripts to large-scale Web applications. Some Web applications contain hundreds of thousands of lines of PHP code, and the fact that PHP can scale to these levels is a great testament to its design and the efficient Zend Engine that actually manages PHP code execution.
Of course, bigger and more complex projects result in more load on your servers, and when you throw a database into the mix you have even more potential performance bottlenecks to track. A typical scenario might be you've added a few new features to a Web application and now are seeing more server load and memory usage; thus, pages seem to load slower. What can you do? Maybe you can afford to throw bigger hardware at the problem, but even if that's a viable option, you also should find the parts of your code that are causing the slowdowns and optimize them.
A number of factors can affect the performance of a Web application, including Web server configuration, database performance, data structure, the application design and the implementation of the application. I'm going to assume you've already taken care of the first items, and now you want to iron out bottlenecks in your application implementation, that is, in the actual code. But how do you find the bottlenecks in the first place?
The answer is a technique known as performance profiling. Performance profiling runs your code in a controlled environment and returns a report listing such statistics as time spent within each function, how long each database query takes and how much memory has been used.
By doing performance profiling on your code, you quickly can see where you may be wasting time with slow database queries or inefficient code. Having this information then allows you to spend your time tuning PHP and SQL where it needs it most. No more guessing what's going on internally: performance profiling gives you hard figures.
If you're really serious about squeezing every last cycle out of the code, you should investigate all the benchmarking tools you can find, because they work in different ways and allow you to extract different kinds of information. For now, however, I'm going to concentrate on APD, the Advanced PHP Debugger.
APD is a debugger written in C by George Schlossnagle and Daniel Cowgill that loads as an extension to the Zend Engine. It works by hooking into the Zend internals and intercepting PHP function calls, allowing it to do things like measure function execution time, count function calls, perform stack backtraces and other funky things.
Currently, three main ways exist to install APD on a Linux system: grab the source and compile it yourself, use PEAR or use the Debian package. The latest source always is available from the APD Web site. Building and installing it isn't a hard process, but you need to make sure the various PHP development resources are installed on your system. For example, you need the PHP C headers, as well as a program called phpize that is used to prepare the package as a Zend extension. If you decide to go that route, make sure you follow the instructions in the README included with the source.
If you use PEAR, included with PHP4.3+, you can install PHP modules with minimal fuss. Once again, the full instructions are available on the APD Web site, which is part of the PEAR project. Assuming PEAR support is included in your version of PHP, getting it going should be as simple as typing pear install apd and answering a few questions.
Finally, for Debian users I maintain a .deb package of the latest version of APD. It's much too recent to be in Woody, but at the time of this writing it's in Sid (current Unstable) and should enter Sarge (current Testing) soon. You should be able to use apt-get install php4-apd to have everything done for you.
Whatever installation method you use, you should have the CGI version of PHP installed, because some of the command-line tools included with APD are written in PHP and need the parser to run. Personally, I run my Web servers with the Apache module version of PHP because it's much faster, but that doesn't matter. Simply install the CGI version of PHP as well and away you go. It doesn't need to affect your Apache module installation of PHP; they can live side by side quite happily.
You can use the phpinfo() function to confirm that APD installed and loaded properly. Create a file in your Web root that calls phpinfo(), and open it in a browser. The quickest way to do that probably is to type
echo '<?php phpinfo() ?>' > info.php
in your Web root. When you access the file in your browser through your Web server (not by directly opening the file), it lists all the extensions that PHP has loaded. You should see APD listed somewhere on the page. If that worked fine, you're ready for the next step.