anchor.diff:                               #had_backfill{};
                            [_,_|_] ->
                                #had_backfill{value = false}
  -                     end
  +                     end,
  +      no_ready_vbuckets = (ReadyVBuckets =:= [])
        },
   
       State1 = process_data(<<>>, #state.downbuf, fun process_downstream/2, State),
  
positive.code:                 %% beneficial. Only ack/nack is getting sent here.
                  ok = inet:setopts(Upstream0, [{nodelay, true}]),
  
                  %% if there's no old state or upstream is
                  %% undefined in it then we promote we'll just
                  %% create a new upstream connection
                  Checkpoints =
                      mc_binary:mass_get_last_closed_checkpoint(DownstreamAux,
                                                                ReadyVBuckets, 60000),
  
                  Args0 = [{vbuckets, ReadyVBuckets},
                          {checkpoints, Checkpoints},
                          {name, TapName},
                          {takeover, TakeOver}],
  
                  ?rebalance_info("Starting tap stream:~n~p~n~p",
                                  [Args0, InitArgs]),
                  {ok, quiet} = mc_client_binary:tap_connect(Upstream0, Args0),
                  {Upstream0, Args0};
              false ->
                  Args0 = [{vbuckets, ReadyVBuckets},
                           {name, TapName},
  
negative.code:                                  "Falling back to old behaviour", [Other]),
                      complete_old_vb_filter_change(State1)
              end;
          true ->
              %% We don't expect this case (though it can still happen). And by
              %% the time new ebucketmigrator starts some of the vbuckets may
              %% have already become ready. It will complicate the logic there
              %% significantly so let's just use old vbucket filter change
              %% approach.
              ?log_warning("Some of new vbuckets are not ready to replicate from. "
                           "Will not use native vbucket filter change. "
                           "Not ready vbuckets:~n~p", [NotReady]),
              complete_old_vb_filter_change(State1)
  