Learned yesterday an important lesson on the Oracle OTN XMLDB forum. A question was asked why a count via a full table scan was quicker than the same example while using an XMLIndex. “XMLIndex performance regarding // (any descendant))”. The poster used the // xpath expression to do his search.
As in most cases nowadays it is important to keep your statistics in order. An XMLIndex is not an “index” as such, it is an logical index / domain index, specially designed for use with XMLDB / XML data.