code: @Override
      public byte[] getKey() {
          StringBuilder sb = new StringBuilder(64);
          sb.append(clusterName).append(MetricUtils.AT).append(topologyId).append(MetricUtils.AT)
                  .append(metaType).append(MetricUtils.AT).append(id);
          return sb.toString().getBytes();
      }
docs: key: clusterName + topologyId + metaType + id