anchor.diff:                  (_, Acc) ->
                       Acc
               end, ok, lists:reverse(DocList)),
  -            Master ! {changes_worker_ans, Ref, SlaveAns}
  +            Master ! {changes_worker_ans, Ref, self(), SlaveAns}
           end)
       end, DocsList).
   
  
positive.code:         DocsGroups = group_changes(Docs),
          DocsList = maps:to_list(DocsGroups),
          Ref = make_ref(),
          parallel_apply(DocsList, Ref),
          Ans = gather_answers(DocsList, Ref),
          Master ! {batch_applied, BatchRange, Ans}
      end),
      ok.
  
negative.code: %% @end
  %%--------------------------------------------------------------------
  -spec parallel_apply([{datastore:key(),
      [datastore:doc()]}], reference()) -> [pid()].
  parallel_apply(DocsList, Ref) ->
      Master = self(),
      lists:map(fun({_, DocList}) ->
          spawn(fun() ->
              SlaveAns = lists:foldl(fun
                  (Doc, ok) ->
  