Fast Web Applications - Design thoughts

Whenever I design web applications there are a number of steps that I go through in order to achieve decent performance. Most of these you will all know about, however there is one thing that I do that does not seem to be well recorded in any book or online article.

Most of you will already have thought about static and dynamic content, in a java web application that will probably mean that there will be a set of HTML pages and images on the apache server and JSPs or Servlets on a Servlet engine.

I have a third classification of content that is very useful to think about: Semi-static.

Semi-static content is content that is data-driven (like dynamic content), but the underlying data changes relatively infrequently compared to the number of times that the content is viewed. Good examples would be a daily graph of stocks or a airport flight information page that is displayed across hundreds of displays.

There are various ways of dealing with this type of content, but they all come down to one thing - caching. Many people when they come across this type of content end up creating a jack-of-all-trades servlet that manages the caching and invalidation of this content. I tend to favour a different approach. I like to generate this content using a template engine (or equivalent for images) to the file system behind my web-server and let the web-server and the downstream caches do their work. The template engine should be event driven, I would normally use a lightweight JMS system to do this.

With a little careful configuration you can leverage the strengths of HTTP to allow an HTTP HEAD request to be issued, checking whether the browser cache, proxy cache or web-server in-memory cache has the up to date version and serve that directly from the cache or retrieve the new version from the web server file system accordingly.