Database Software

In my xpath, I need to use the "xsi" namespace to specify the xpath condition. It seems to be the performance of the xpath that uses the "xsi" namespace is extremly slow, compared with a similar xpath that does not use the name space, although the number of retrieved objects are the same in my test case.

What causes such a big difference in speed? Is that possible when I use the "xsi" namespace in the xpath, the xpath is not get rewritten? How can I improve the performance when using "xsi" namespace.

1)xpath not use the namespace
select extract(object_value, '/Test/Group/Object[uniqueName="a1"from Test where existsNode(object_value, '/Test/Group[uniqueName="N10001"])=1;

2)xpath use the "xsi" namespace
select extract(object_value, '/Test/Group/Object[uniqueName="a1" and @xsi:type="Architecture"]', 'xmlns="http://www.myspace.com/testXML" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"') from Test where existsNode(object_value, '/Test/Group[uniqueName="N10001"])=1;