private void updateScanNum(PlanNode planNode, Map<Path, AtomicInteger> pathSumMap) {
    if (planNode instanceof LastSeriesSourceNode) {
      LastSeriesSourceNode lastSeriesSourceNode = (LastSeriesSourceNode) planNode;
      pathSumMap.merge(
          lastSeriesSourceNode.getSeriesPath(),
          lastSeriesSourceNode.getDataNodeSeriesScanNum(),
          (k, v) -> {
            v.incrementAndGet();
            return v;
          });
    }
    planNode.getChildren().forEach(node -> updateScanNum(node, pathSumMap));
  }
A simple implementation of IFragmentParallelPlaner. This planner will transform one PlanFragment
into only one FragmentInstance.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/distribution/SimpleFragmentParallelPlanner.java