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