High Performance Web Sites blog

It’s important to make resources (images, scripts, stylesheets, etc.) cacheable so your pages load faster when users come back. A recent study from Website Optimization shows that the top 1000 home pages average over 50 resources per page! Being able to skip 50 HTTP requests and just read those resources from the browser’s cache dramatically speeds up pages.

This is covered in my book (High Performance Web Sites) and YSlow by Rule 3: Add an Expires Header. It’s easy to make your resources cacheable – just add an Expires HTTP response header with a date in the future. You can do this in your Apache configuration like this:

<FilesMatch "\.(gif|jpg|js|css)$">
  ExpiresActive On
  ExpiresDefault "access plus 10 years"
</FilesMatch>

That part is easy. The hard part is revving your resource filenames when you make a change. If you make mylogo.gif cacheable for 10 years and then publish a modified version of this file to your servers, users with the old version in their cache won’t get the update. The solution is to rev the name, perhaps by including the file’s timestamp or version number in the URL. But which is better: mylogo.1.2.gif or mylogo.gif?v=1.2? To gain the benefit of caching by popular proxies, avoid revving with a querystring and instead rev the filename itself. Continue Reading »

I was in Portland for OSCON last week. There were many talks that attracted my attention - so many that I couldn’t get to them all. If you missed some talks, or didn’t make it to OSCON, check out this great effort capturing Oscon in 37 minutes. Gregg Pollack asked 45 speakers to summarize their talk in 30 seconds. Most people took longer (37 * 60 / 45 = 49.3 seconds), but still, to get a taste of 45 sessions in a 37 minute video is pretty awesome. If you had attended each session it would’ve taken over 34 hours! You can jump straight to the segment for any speaker (here’s mine), and links to each speaker’s slides are displayed.

Eric Miraglia wrote a post yesterday called Combo Handler Service Available for Yahoo-hosted JS. One of the advantages of YUI over other JavaScript frameworks is its à la carte capabilities. Developers can choose just the parts they want, rather than being saddled with the whole kit and caboodle. It’s great to download fewer bytes, but choosing a subset of modules results in downloading multiple external scripts, something that’s bad for performance and costs YSlow points. That’s where Eric’s post comes in.

The Combo Handler Service lets developers choose a customized subset of modules and have them served as a single HTTP request from Yahoo!’s worldwide CDN for faster delivery. Each module (file) is listed in the querystring. As an example, Eric shows that loading the YUI Rich Text Editor the old way would require downloading six separate scripts:

<script src=”http://yui.yahooapis.com/2.5.2/build/yahoo-dom-event/yahoo-dom-event.js”>
</script>
<script src=”http://yui.yahooapis.com/2.5.2/build/container/container_core-min.js”>
</script>
<script src=”http://yui.yahooapis.com/2.5.2/build/menu/menu-min.js”>
</script>
<script src=”http://yui.yahooapis.com/2.5.2/build/element/element-beta-min.js”">
</script>
<script src=”http://yui.yahooapis.com/2.5.2/build/button/button-min.js”>
</script>
<script src=”http://yui.yahooapis.com/2.5.2/build/editor/editor-beta-min.js”>
</script>

This is reduced to a single HTTP request by using the Combo Handler:

<script src=”http://yui.yahooapis.com/combo?2.5.2/build/yahoo-dom-event/yahoo-dom-event.js&
2.5.2/build/container/container_core-min.js&2.5.2/build/menu/menu-min.js&
2.5.2/build/element/element-beta-min.js&2.5.2/build/button/button-min.js&
2.5.2/build/editor/editor-beta-min.js”>
</script>

It’s important that developers using Combo Handler pay particular attention that they get the dependency order correct. I created the YUI Combo Handler: preserving order test page to show what happens if prerequisites are listed incorrectly. In this page instead of putting editor-beta-min.js as the last querystring parameter, I make it the first parameter. Not surprisingly, the page produces JavaScript errors. It would be great if Combo Handler ensured that the response had all the necessary prerequisites in the right order. With this enhancement the single request would be much simpler:

<script src=”http://yui.yahooapis.com/combo?2.5.2/build/editor/editor-beta-min.js”>
</script>

This is a great announcement. Web developers using YUI can now get a customized rollup hosted on Yahoo!’s CDN! This is the best of all worlds - reduced download size, fewer HTTP requests, and CDN hosting. I encourage other JavaScript frameworks to adopt YUI’s à la carte flexibility. Perhaps Google Ajax Libraries could then support features to serve up customized builds similar to what Combo Handler does. Well done.

Writing faster web pages is great for your users, which in turn is great for you and your company. But it’s better for everyone else on the planet, too.

Intrigued by an article on Radar about co2stats.com, I looked at my web performance best practices from the perspective of power consumption and CO2 emissions. YSlow grades web pages according to how well they follow these best practices. What if it could convert those grades into kilowatt-hours and pounds of CO2?

Continue Reading »