This is article #1 of a 4-part series. This article (along with Article #2) serves as a primer for the last two entries in this series, which discuss the most efficient way to put these concepts into practice in your web application. For more a more in-depth look at these concepts, see Yahoo!'s Best Practices for Speeding Up Your Web Site and Google's Speed Tracer tutorial
Page load speed is becoming increasingly important as rich web applications become more interactive. It's not just about usability anymore; it can now directly affect your placement in search engine results, now that Google uses page load speed in their ranking algorithm. Are you ready for a reality check? Get Google Webmaster Tools for your site, and go to the Labs >> Site Performance to view your average page load time, as seen by Google's web crawlers. That's right, Google is already tracking your site's performance history.
Google Webmaster Tools is even kind enough to tell you how you stack up against the rest of the web. Here is what Webmaster Tools had to say about one of our sites before optimizing it for quick page loading:
On average, pages in your site take 4.5 seconds to load (updated on Feb 21, 2010). This is slower than 70% of sites. These estimates are of low accuracy (fewer than 100 data points). The chart below shows how your site's average page load time has changed over the last few months. For your reference, it also shows the 20th percentile value across all sites, separating slow and fast load times.
Ouch. Did I mention this would be a painful reality check?
Now to be fair, there's a very reasonable explanation for this. Google claims that the majority of users will click "back" to the search results page if a link takes too long to load. So, if a webpage is too slow for the visitor to read it, the relevance of the content is...well, irrelevant. I should point out, however, that it's unknown precisely how much page load speed affects your placement in search results.
80-90% of the end-user response time is spent downloading all the components in the page: images, stylesheets, scripts, Flash, etc.
Continue to Article #2, which focuses on reducing the time it takes visitors to download your site's assets by up to 90%. That means your site will load up to 2-3x faster.