@Override
  public String toString() {
    return toStringHelper(this)
        .add("level", level)
        .add("levelScheduledTime", levelScheduledTime)
        .toString();
  }
Occupied time in particular level of this task. The higher this value is, the later the task
with this Priority will be polled out by a PriorityQueue.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/schedule/queue/multilevelqueue/Priority.java