I really enjoyed Jeremy Kemper’s talk on wednesday. The sort of talk that has you itching to run home and try out what you’ve seen. All good stuff. For those of you who weren’t there, Jeremy was talking about performance.

The key point is that it’s all about the user experience: how fast do our users think the app is? Part of it is your ruby code (and Jeremy had plenty to say about that, with GC tips, profiling tips etc…) but a huge chunk is the network. A common trick is to bundle up your assets, what with the limit on the number of concurrent loads from a domain and the part that latency plays, loading 1 medium or biggish javascript (or stylesheet file or whatever) is almost always preferable to 5 small files. With 2.1 Rails makes this easy and will bundle up your js for you, but there’s another trick you can play.

You could stick assets like your javascript files on some sort of content distribution network, close to your users wherever they are. This would be an inordinate amount of effort to go to though just to host a few javascript files. Luckily, google has done that for you with their Ajax Libraries API. They are hostting copies of common javascript frameworks, including prototype, scriptaculous, dojo, jquery and mootools. You get to use their content distribution network and can assume they’ve got all the caching and compression stuff done right. The libraries are all versioned too (ie you say ‘give me prototype 1.6.0.1’), so no worries about that.

There is of course another advantage: instead of your browser caching a copy of prototype.js from every site that uses it, your users will only be caching it once (per version). Chances are when they come to your site it will already be in the cache.

Jeremy also mentioned the importance of putting yourself in your users shoes and seeing what your webapp is like when viewed through a slow or high(er) latency connection. I described one way of doing this alternative a few months ago and it really can be quite the eye-opener.