Besides proper configuration of HTTP caching headers, enabling gzip compression is typically the most important technique for speeding up your web page. A chapter was devoted to compression in Steve Souders’ first book, High Performance Web Sites. Now that all browsers support gzip and all responsible web developers have enabled gzipping, that chapter is closed, right? Not quite.
Even if you have enabled gzipping, there is a good chance that a small but significant portion of visitors to your site are not receiving compressed responses. The exact percentage varies greatly across different demographics and geographies, but a large web site in the United States should expect that roughly 15% of visitors don’t indicate gzip compression support. This chapter explains why the percentage is higher than expected, how that affects performance, and what developers can do about it.
With such a small percentage, you might ask, “What’s the big deal?” Let’s take a look at what happens to 10 popular web sites when gzipping is disabled.
In this experiment, the page load time for 10 popular web sites was measured by loading each web site 100 times in Internet Explorer 7.0 on Windows XP Pro. The cache remained primed between iterations to better represent the typical experience. All requests traveled through a proxy (Eric Lawrence’s Fiddler) on the same machine. In the control group the proxy did nothing, but in the experimental ...