protected Event supplyHeartbeat(final PipeRealtimeEvent event) {
    if (event.increaseReferenceCount(PipeRealtimeDataRegionExtractor.class.getName())) {
      return event.getEvent();
    } else {
      // This would not happen, but just in case.
      LOGGER.error(
          "Heartbeat Event {} can not be supplied because "
              + "the reference count can not be increased",
          event.getEvent());

      // Do not report exception since the PipeHeartbeatEvent doesn't affect
      // the correction of pipe progress.

      return null;
    }
  }
@param event the {@link Event} from the {@link StorageEngine}
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/pipe/extractor/dataregion/realtime/PipeRealtimeDataRegionExtractor.java