Major Description
CollapsingQParserPlugin should not run scorer for documents not eligible for collapsing (in cases when score is not needed for collapsing operation) but only for the result sorting, decoration of result fields or boosting.
Performance improvement example:
2_000_000 documents collapsed by sort without score to 130_000 then sorted by score improved from 4300ms to 2700ms
I am attaching patch on master branch.