Nowadays, even regular Web surfers know some of the things to do when designing a Web site for fast performance. Cut the number of requests to the Web server. Shrink JPEG sizes. Enlist the services of a content delivery network vendor like Akamai Technologies Inc. or Limelight Networks Inc.
Problem is, according to Steve Souders, steps like those, which are aimed at optimizing the Web server, make only a tiny impact.
“We used to tear apart the Apache [Web server] code to figure out what Yahoo was doing,” said Souders, who was Yahoo Inc.'s chief performance engineer for several years before moving to Google Inc. in the same role.
But after performing a detailed analysis, Souders discovered something startling: Only 10% to 20% of the time it took to load a Web site could be attributed to the Web server.
The vast majority was the result of code executing inside the Web browser, said Souders at a talk at Microsoft Corp.'s Tech Ed conference in Los Angeles.
That might have made sense a decade ago, but in today's era of PCs powered by dual- and quad-core CPUs, it doesn't. And the cost of the delays created can be high.
Google has found that a 500-millisecond delay results in a 20% decrease in Web traffic, while Amazon.com Inc. has seen a 100-millisecond delay cutting its sales by 1%, Souders said.
Better browsers, better performance
To fix the problem, Souders first recommends a free tool he created called Yslow, which analyzes and then grades how well a Web page is designed for maximum speed. Originally developed for IE, Yslow 2.0 is an add-on for Firefox integrated with the Firebug Web development tool. It can be downloaded on the Yahoo Developer Network.
Doing that helped one Google site that Souders declined to name speed up its initial page rendering by 60%.
Cascading Style Sheets (CSS) can also drag down site performance. CSS files, which describe a Web page's look and feel, have become more elaborate in recent years.
CSS files are a problem in part because users tend to stay on certain CSS-heavy sites, such as Web mail portals, all day. These sites will re-render constantly throughout the day, producing a delay attributable to overelaborate CSS files each time, Souders said.
“When I look at it, I feel like the teacher who hands out very severe grades,” Souders said. Search engines with minimal content on the page, such as Google.com and Microsoft's Live.com, are among the rare sites that get an A from Yslow.
There are other tools besides Yslow for diagnosing performance bottlenecks. Microsoft offers Visual Roundtrip Organizer, and AOL developed a now-open-source tool called PageTest.
All of those tools judge Web site performance by a set of rules, though none of them matches Yslow's 22 criteria.