org.zkoss.poi.xssf.usermodel.XSSFPivotCache.IndexMapper#IndexMapper

iterates over Lists returned by

org.openxmlformats.schemas.spreadsheetml.x2006.main.CTSharedItems#getNList

Iteration over the returned lists is highly inefficient causing hundreds of millions of method calls when e.g. exporting a pivottable with 20000 rows / 6 columns

this needs to be patched in zpoiex.jar