Thursday, November 30, 2006

Performance Research, Part 1: What the 80/20 Rule Tells Us about Reducing HTTP Requests

Website loading speed is part of usability ...

"It’s no secret that users prefer faster web sites. I work in a dedicated team focused on quantifying and improving the performance of Yahoo! products worldwide. As part of our work, we conduct experiments related to web page performance. We are sharing our findings so that other front-end engineers join us in accelerating the user experience on the web.

The 80/20 Performance Rule
Vilfredo Pareto, an economist in the early 1900s, made a famous observation where 80% of the nation’s wealth belonged to 20% of the population. This was later generalized into what’s commonly referred to as the Pareto principle (also known as the 80-20 rule), which states for any phenomenon, 80% of the consequences come from 20% of the causes. We see this phenomenon in software engineering where 80% of the time is spent in only 20% of the code. When we optimize our applications, we know to focus on that 20% of the code. This same technique should also be applied when optimizing web pages. Most performance optimization today are made on the parts that generate the HTML document (apache, C++, databases, etc.), but those parts only contribute to about 20% of the user’s response time. It’s better to focus on optimizing the parts that contribute to the other 80%.

Using a packet sniffer, we discover what takes place in that other 80%. Figure 1 is a graphical view of where the time is spent loading with an empty cache. Each bar represents a specific component and is shown in the order started by the browser. The first bar is the time spent for the browser to retrieve just the HTML document. Notice only 10% of the time is spent here for the browser to request the HTML page, and for apache to stitch together the HTML and return the response back to the browser. The other 90% of the time is spent fetching other components in the page including images, scripts and stylesheets."    (Continued via Yahoo! User Interface Blog)    [Usability Resources]

Yahoo Loading Time - Usability, User Interface Design

Yahoo Loading Time


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