@Override
  public Operator visitFill(FillNode node, LocalExecutionPlanContext context) {
    Operator child = node.getChild().accept(this, context);
    return getFillOperator(node, context, child);
  }
This Visitor is responsible for transferring PlanNode Tree to Operator Tree.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/OperatorTreeGenerator.java