fields.add("id");
outputs.put(ACKER_ACK_STREAM_ID, Thrift.directOutputFields(fields));
outputs.put(ACKER_FAIL_STREAM_ID, Thrift.directOutputFields(fields));
IBolt ackerbolt = new Acker();
// generate inputs
Map<GlobalStreamId, Grouping> inputs = acker_inputs(ret);
// generate acker which will be stored in topology