The RangePreserver is an RAII class which opens a special ClientCursor on construction, and deletes it on destruction. The purpose of this ClientCursor is to allocate a special cursor id whose presence will prevent the deletion of chunk ranges which might still be needed by an active query.

The planned work in SERVER-27760 will remove the use of cursor ids for determining which chunk ranges can be cleaned up. Therefore, once SERVER-27760 is resolved, uses of the RangePreserver can be removed and the class can be deleted.