I've noticed that the current performance of xml parsing is pretty bad. I've got a patch ready to go to improve this substantially. On our internal deployment it has cut down memory and CPU usage substantially and has significantly improved overall response time.
Most of the changes that need to be made are compatible with fairly old xml parsers, but not so many work with pooling DocumentBuilders. For instance, xerces needs to be upgraded (I'm using 2.8.1, which is about 2 years old, and that works). Does anyone have any strong objections to upgrading xerces, or are there any instances of xml parsers being used that also don't support DocumentBuilder.reset ?
