elasticsearch/elasticsearch — pull request #6523 by jpountz (2014-06-16 23:56:41+00:00)
Title: Mappings: Allow _version to use `disk` as a doc values format.

VersionFieldMapper.defaultDocValuesFormat claims that the default is `disk`
(which is wrong, it's using Lucene's defaults).
This is not used to choose the DV format in the index but for mappings
serialization in order to know when the _version doc values format is
different from the default format. This made it impossible to use the `disk`
doc values format since mappings would never retain that information at
serialization time.