The goal of web performance optimization is to become faster and smaller: research at Yahoo! and Google found that just 10-20% of the perceived loading time is caused by the server. A few years ago we thought performance was exclusively connected to the server. However, 80-90% of the loading time incurs in the frontend. Thus WPO is more efficient targeting the frontend.

Two important weak points are JavaScript files and the sheer number of files: JavaScript loads sequentially and blocks subsequent code until each file is loaded. Hence it shouldn’t be located in the head, but in the foot of a page. Secondly older browsers, in particular Internet Explorer, will only load 2-4 files in parallel. Files queue up and get processed when it’s their turn. Therefore aggregation of files is used for reducing the number of HTTP requests.

Several international companies have conducted research or just tracked the effects of optimization.

Effects of slowness

• Amazon: 100 ms delay caused a 1% drop in revenue.
• Google: 400 ms delay caused a 0.59% decrease in search requests per user (earlier tests list larger numbers).
• Yahoo!: 400 ms delay caused a 5-9% decrease in traffic.
• Bing: 2 seconds delay caused a 4.3% drop in revenue per user.

Effects of speed

• Mozilla made their download page 2.2 seconds faster and was rewarded with an increase of 15.4% in downloads.
• Google Maps reduced the file volume by 30% and observed a 30% increase in map requests.
• Netflix enabled gzip on the server; simply by this single action pages became 13-25% faster and saved 50% of traffic volume!
• Shopzilla succeeded in reducing the loading time from 7 down to 2 seconds, whereby the conversion rate increased by 7-12%, they observed a 25% increase in page requests, they were able to retire 50% of their servers, thus saving energy costs.
• AOL observed the number of page views on several websites. While the fastest users requested 7-8 pages, the slowest only viewed 3-4.

As a cream topping Google recently announced to factor in the site speed as a parameter in web search ranking.

Eventually pages become faster, clients are happy, generate more revenue and page views, while power consumption and CO₂ emissions decrease. Saved the world, again! And if you’d like to contribute, start by checking the rules at Yahoo! A few tricks beyond that can be found in the presentation which will be translated soon.