@Override
  public boolean equals(Object o) {
    if (this == o) {
      return true;
    }
    if (o == null || getClass() != o.getClass()) {
      return false;
    }
    PlanFragment that = (PlanFragment) o;
    return Objects.equals(id, that.id) && Objects.equals(planNodeTree, that.planNodeTree);
  }
PlanFragment contains a sub-query of distributed query.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/planner/plan/PlanFragment.java