anchor.diff:  init([ReqId, {VNode, System}, Op, From, Entity, Val]) ->
       {ok, N} = application:get_env(dalmatiner_db, n),
       {ok, R} = application:get_env(dalmatiner_db, r),
  -    SD = #state{req_id=ReqId,
  -                r=R,
  -                n=N,
  -                from=From,
  -                op=Op,
  -                val=Val,
  -                vnode=VNode,
  -                system=System,
  -                entity=Entity},
  +    Compression = application:get_env(dalmatiner_db,
  +                                      metric_transport_compression, snappy),
  +
  +    SD = #state{req_id = ReqId,
  +                compression = Compression,
  +                r = R,
  +                n = N,
  +                from = From,
  +                op = Op,
  +                val = Val,
  +                vnode = VNode,
  +                system = System,
  +                entity = Entity},
       {ok, prepare, SD, 0}.
   
   %% @doc Calculate the Preflist.
  
positive.code:     SD#state{replies = Replies};
  save_reply(IdxNode, Obj, SD = #state{system = metric, replies = Replies0}) ->
      {Res, Metrics} = Obj,
      Replies = [{IdxNode, {Res, decompress(Metrics)}} | Replies0],
      SD#state{replies = Replies}.
  
  -spec merge(state(), [E]) -> E.
  
negative.code: %%-type metric_reply() :: {partition(), metric_element()}.
  
  -record(state, {req_id,
                  compression :: snappy | none,
                  from,
                  entity,
                  op,
  