Oracle OCI JDBC Driver problems

Yesterday, I spent a couple of hours trying to work out why we were getting an UnsatisfiedLinkError on the OCI8 libraries when we were running the 9.2 JDBC OCI drivers against an Oracle 9.2 database on Windows Server 2003.

After a lot of head scratching it turned out that the application's ojdbc14.jar and the OCI libraries were mutually incompatible despite appearing to be for the same point release of Oracle.

The application's driver jar was the one that was checked into CVS, whereas the libraries came as part of a new install of Oracle. When we used the driver jar from the new install, our problems went away.

It is definitely worth remembering to always use the driver jars that came with the libraries that you are using.

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.