Nowadays, even regular Web surfers know some of the things to avoid when designing a Web site for fast performance. Cut the number of requests to the Web server. Shrink JPEG sizes. Employ a content delivery network vendor like Akamai Technologies Inc. or Limelight Networks Inc.
Problem is, according to Steve Souders, steps like these 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 on Tuesday at Microsoft Corp.'s Tech Ed conference in Los Angeles (download PowerPoint here)
That may 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 has seen a 100 millisecond delay cutting its sales by 1%, Souders said.
Better browsers, better performance
To fix, Souders first recommends a free tool he created called Yslow that analyzes and then grades how well a Web page is designed for maximum speed. Originally developed for Internet Explorer, Yslow 2.0 is an add-on for Firefox integrated with the Firebug Web development tool. It is downloadable here.
Doing so helped one Google site that Souders declined to name speed up its initial page rendering by 60%.
Also, users tend to stay on certain sites, such as their Web mail, all day. These sites will re-render constantly throughout the day, incurring a delay from over-elaborate CSS files each time, Souders said.
"When I look at it, I feel like the teacher who hands out very severe grades," he 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.
All these tools judge Web site performance by a set of rules, though none of them matches YSlow's 22 criteria.