@Override
  protected void clearAllElements() {
    highestPriorityLevelQueue.clear();
    for (PriorityQueue<DriverTask> level : levelWaitingSplits) {
      level.clear();
    }
  }
During periods of time when a level has no waiting splits, it will not accumulate scheduled
time and will fall behind relative to other levels.

<p>This can cause temporary starvation for other levels when splits do reach the
previously-empty level.

<p>To prevent this we set the scheduled time for levels which were empty to the expected
scheduled time.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/schedule/queue/multilevelqueue/MultilevelPriorityQueue.java