elasticsearch/elasticsearch — pull request #6197 by martijnvg (2014-05-15 21:33:41+00:00)
Title: Entirely cut over to TopDocs#merge for merging shard docs in the reduce phase 

From Lucene 4.8 the TopDocs#merge supports slicing of the shard level top docs, by taking the offset into account (for pagination). Because of this the custom shard level topdocs merging can be removed in favour for TopDocs#merge.