XML Index again

[Chris Roffler <croffler@xxxxxxxxxxxxx>]

I still have some problems with my xml index

CREATE INDEX xml_index

  ON time_series

  USING btree

  ((

  (xpath('/AttributeList/Attributes/Attribute/Name/text()', external_attributes))[1]::text));

When I run the following query the index is not used :

select id from time_series where  

array_upper(

(xpath('/AttributeList/Attributes/Attribute[Name="Attribute122021"]', external_attributes))

, 1) > 0

Any Idea on how to configure the index ?

Thanks

Chris