PHP Performance Profiling

To get the best understanding of how your PHP implementation runs under real conditions, you should do the profiling in an environment as close as possible to the real thing. Real data and many real or simulated client connections are helpful. You can create this environment by making a duplicate of your site and running HTTP benchmarking software or even using a couple of shell scripts and Wget to simulate user loads. Alternatively, you can do the profiling right on your live site.

As you've seen, using the profiling features of APD in your scripts causes the Web server to write out text files for every script access. That's obviously a very bad thing if you're trying to profile a live site, because data is dumped out faster than you can deal with it. Besides, it causes a slowdown on the server if your site has a lot of visitors--and if it didn't, you wouldn't be profiling it, would you? A useful little trick to get around the problem is to activate profiling only for page requests coming from your specific IP address. Doing so allows you to browse the live site and produce profile information without any action being taken on requests by other users.

This situation actually is pretty trivial to implement. Simply wrap the invocation of apd_set_pprof_trace() in a check for the requesting IP address, as shown below. Then, only your nominated client addresses cause the script to go into profiling mode:

        <?php
        $DEBUGIPS = array('203.222.90.204','192.168.0.23');
        if(array_search($_SERVER[REMOTE_IP], $DEBUGIPS)) {
                apd_set_pprof_trace();
        }
        ?> 

What now? Optimize your code, of course. I'm not going to tell you how to do that here, because it's way beyond the scope of this short article. But, at least now you have some insight into the internal workings of your application and won't be wasting time optimizing parts of your code that aren't really a problem. And when you do make changes, you have a benchmark against which you can test your code to see how the changes affect performance and efficiency.

Jonathan Oxer is the founder and Technical Director of Internet Vision Technologies, an Australian Web application development agency with clients around the world. He also is a Debian developer, current maintainer of apt-cacher and was organizer of the Debian Mini-Conf in Perth in January 2003 in association with Linux Conf Australia, where he also presented one of the technical papers. His first book, How to Hire a Web Developer and Stay Sane, will be published soon. His second book, The Debian Universe is being written live on-line, and his third and fourth books (How to Deploy Web Applications and Stay Sane and Disaster Proofing for Small Networks) already are underway.