This patch (on the trunk from a couple of weeks ago) provides the ability for Esper to use the Apache Axiom XML library. Axiom provides a DOM-like tree view, including XPath, but still supports Streaming behaviour via the StAX API. The benefit of this is that it will only parse enough of the message/event to evaluate the required XPaths. Some tests that one of my colleagues (Sanka) did have shown a big speedup compared to DOM. Let me know if this needs updating to the latest trunk.