@Override
  public Duration getTotalCpuTime() {
    return null;
  }
QueryScheduler is used to dispatch the fragment instances of a query to target nodes. And it will
continue to collect and monitor the query execution before the query is finished.

<p>Later, we can add more control logic for a QueryExecution such as retry, kill and so on by
this scheduler.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/scheduler/ClusterScheduler.java