MatrixAdapt | Logiciel de gestion d'Entreprise, Création et référencement des sites web

• You must instrument your site (one example tool is jiffy-web).
• You must isolate changes.
  • The most straight-forward way to do that is to release only one change at a time. That avoids having multiple changes altering performance numbers--for better or for worse--at the same time.
• Consider releasing changes to a subset of users.
  • That helps safe-guard against real-world events like holidays, big news days, exploding hard drives, and, perhaps the worst possible fate of all: a slashdotting.

• Firefox Throttle (Firefox plug-in, windows-only, free)
• Fiddler: Web Debugging Proxy (free)
• Charles: Web Debugging Proxy (shareware, $50)

• Page Speed, an open source Firefox/Firebug add-on that evaluates the performance of web pages and gives suggestions for improvement.
• YSlow, a free tool from Yahoo! that suggests ways to improve website speed.
• WebPagetest shows a waterfall view of your pages' load performance plus an optimization checklist.
• In Webmaster Tools, Labs > Site Performance shows the speed of your website as experienced by users around the world as in the chart below. We've also blogged about site performance.

• Many other tools on code.google.com/speed.

• Prepare a lightweight version of your site.
  Consider maintaining a lightweight version of your website; you can then switch all of your traffic over to this lightweight version if you start to experience a spike in traffic. One good way to do this is to have a mobile version of your site, and to make the mobile site available to desktop/PC users during periods of high traffic. Another low-effort option is to just maintain a lightweight version of your homepage, since the homepage is often the most-requested page of a site as visitors start there and then navigate out to the specific area of the site that they’re interested in. If a particular article or picture on your site has gone viral, you could similarly create a lightweight version of just that page.
  A couple tips for creating lightweight pages:
• Exclude decorative elements like images or Flash wherever possible; use text instead of images in the site navigation and chrome, and put most of the content in HTML.
• Use static HTML pages rather than dynamic ones; the latter place more load on your servers. You can also cache the static output of dynamic pages to reduce server load.
• Take advantage of stable third-party services.
  Another alternative is to host a copy of your site on a third-party service that you know will be able to withstand a heavy stream of traffic. For example, you could create a copy of your site—or a pared-down version with a focus on information relevant to the spike—on a platform like Google Sites or Blogger; use services like Google Docs to host documents or forms; or use a content delivery network (CDN).
• Use lightweight file formats.
  If you offer downloadable information, try to make the downloaded files as small as possible by using lightweight file formats. For example, offering the same data as a plain text file rather than a PDF can allow users to download the exact same content at a fraction of the filesize (thereby lightening the load on your servers). Also keep in mind that, if it’s not possible to use plain text files, PDFs generated from textual content are more lightweight than PDFs with images in them. Text-based PDFs are also easier for Google to understand and index fully.
• Make tabular data available in CSV and XML formats.
  If you offer numerical or tabular data (data displayed in tables), we recommend also providing it in CSV and/or XML format. These filetypes are relatively lightweight and make it easy for external developers to use your data in external applications or services in cases where you want the data to reach as many people as possible, such as in the wake of a natural disaster.

Yes. WebPagetest.org can test performance from the United States (both East and West Coast—go West Coast! :), United Kingdom, China, and New Zealand.

First, if your competition is fast, they may provide a better user experience than your site for your same audience. In that case, you may want to make your site better, stronger, faster...

Otherwise, studies by Akamai claim 2 seconds as the threshold for ecommerce site "acceptability." Just as an FYI, at Google we aim for under a half-second.

Definitely! Progressive rendering is when a browser can display content as it’s available incrementally rather than waiting for all the content to display at once. This provides users faster visual feedback and helps them feel more in control. Bing experimented with progressive rendering by sending users their visual header (like the logo and searchbox) quickly, then the results/ads once they were available. Bing found a 0.7% increase in satisfaction with progressive rendering. They commented that this improvement compared with full feature rollout.

How can you implement progressive rendering techniques on your site? Put stylesheets at the top of the page. This allows a browser to start displaying content ASAP.

1. Split the initial payload
2. Load scripts without blocking
3. Don't scatter scripts
4. Split dominant content domains
5. Make static content cookie-free
6. Reduce cookie weight
7. Minify CSS
8. Optimize images
9. Use iframes sparingly
10. To www or not to www

• Combined and minimized JavaScript and CSS files used throughout the site

• Implemented CSS sprites for frequently-used images

• Implemented lazy loading of Google AJAX APIs loader module (google.load)
  

    <script type="text/javascript" src="http://www.google.com/jsapi"></script>

if (needToLoadGoogleAjaxApisLoaderModule) {
    // Load Google AJAX APIs loader module (google.load)
    var script = document.createElement('script');
    script.src = 'http://www.google.com/jsapi?callback=googleLoadCallback';
    script.type = 'text/javascript';
    document.getElementsByTagName('head')[0].appendChild(script);
}

function googleLoadCallback() {
  // Initialize AJAX Feed API
  google.load('feeds', '1', {callback: startUsingAjaxFeedAPI});
}

function startUsingAjaxFeedAPI() {
  // Start using AJAX Feed API
  var feed = new google.feeds.Feed(someFeedUrl);
  ...
}

• Doug Crockford: JavaScript: The Good Parts
• John Resig: Drop-in JavaScript Performance