Forget about using XML::SImple for large XML files. It will take quite a lot more memory than the file size to load XML via XML::Simple.

I'd recommend XML::Twig (and keep the fhe flush() method in mind).

update: XML::Twig also has much better search methods for finding the tags you're interested in (and ignoring the rest). XML::Simple is more useful if the XML is fairly small and already more or less matches your desired data structure.