I'm moving into the XML space and one of the things I see is that XML processing is very expensive, so AxKit, PageKit, et al make extensive use of caching. I'm keeping all of my data in a MySQL DB with about 40 tables. I'm pretty clear about how to turn that MySQL data into XML and turn the XML into HTML, WML, or what have you. But I haven't been able to wrap my skull around knowing when the data in Mysql is fresher than what is in the cache without doing a major portion of the work needed to generate that web page to begin with.
Do AxKit and PageKit pay such close attention to caching because XML processing is so deadly slow that one doesn't have a hope of reasonable response times on a fast but lightly loaded server otherwise? Or is it because even a fast server would quickly be on its knees under anything more than a light load? With a MVC type architecture, would it make sense to have the Model objects maintain the XML related to the content I want to serve as static files so that a simple stat of the appropriate XML file tells me if my cached HTML document is out of date? One more thing. Perrin Harkins' eToys case study casually mentions a a means of removing files from the mod_proxy cache directory so that mod_proxy had to go back to the application servers to get an up to date copy. I haven't seen anything in the mod_proxy docs that says this is possible. Does something like that exist outside of eToys? I don't know, maybe my Prussian Perfection gene has taken over again and wants a bigger win than I need to get ... -- Christopher L. Everett Chief Technology Officer The Medical Banner Exchange Physicians Employment on the Internet
