private void recordPlanNodeRelation(PlanNode root, PlanFragmentId planFragmentId) {
    planNodeMap.put(root.getPlanNodeId(), new Pair<>(planFragmentId, root));
    for (PlanNode child : root.getChildren()) {
      recordPlanNodeRelation(child, planFragmentId);
    }
  }
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