private Map<String, InputLocation> constructSourceColumnToInputLocationMap(PlanNode node) {
    Map<String, InputLocation> sourceColumnToInputLocationMap = new HashMap<>();
    Map<String, List<InputLocation>> layout = makeLayout(node);
    for (Map.Entry<String, List<InputLocation>> layoutEntry : layout.entrySet()) {
      sourceColumnToInputLocationMap.put(layoutEntry.getKey(), layoutEntry.getValue().get(0));
    }
    return sourceColumnToInputLocationMap;
  }
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