anchor.diff:                        ?DEFINE_SUBTRACTOR(queue_drain),
                         ?DEFINE_SUBTRACTOR(queue_backoff),
                         ?DEFINE_SUBTRACTOR(queue_backfillremaining),
  -                      ?DEFINE_SUBTRACTOR(queue_itemondisk)}.
  +                      ?DEFINE_SUBTRACTOR(queue_itemondisk),
  +                      ?DEFINE_SUBTRACTOR(total_backlog_size)}.
   -undef(DEFINE_SUBTRACTOR).
   
   -endif. % NEED_TAP_STREAM_STATS_CODE
  
positive.code:                       ?DEFINE_ADDER(queue_drain),
                        ?DEFINE_ADDER(queue_backoff),
                        ?DEFINE_ADDER(queue_backfillremaining),
                        ?DEFINE_ADDER(queue_itemondisk)}.
  -undef(DEFINE_ADDER).
  
  -define(DEFINE_SUBTRACTOR(N), N = A#tap_stream_stats.N - B#tap_stream_stats.N).
  
negative.code: ?DEFINE_EXTRACT(backoff, queue_backoff);
  ?DEFINE_EXTRACT(backfill_remaining, queue_backfillremaining);
  ?DEFINE_EXTRACT(itemondisk, queue_itemondisk);
  ?DEFINE_EXTRACT(total_backlog_size, total_backlog_size);
  ?DEFINE_EXTRACT(count, count);
  extract_agg_stat(_K, _V, Acc) -> Acc.
  -undef(DEFINE_EXTRACT).
  