Don't Use REXML. I Mean It.
REXML is the standard XML processing library for Ruby. It’s on Ruby’s core and is terribly slow.
Yeah, I know it’s pretty simple to use, got a nice interface and, again, it’s just there. And it is a good library, for most things. But if you, as me, came to a point that processing XML is taking 50% of the time to render a rails action, it’s time to change.
My tip? Use libxml instead. The numbers on their home page speak for themselves. Try it yourself, you won’t be disappointed. And I’m really happy with the performance increase on our app.