public void start() {
    long now = System.currentTimeMillis();
    ignoreNotExistsDevice = !StorageEngine.getInstance().isReadyForNonReadWriteFunctions();
    executionStartTime.compareAndSet(null, now);
    startNanos.compareAndSet(0, System.nanoTime());

    // always update last execution start time
    lastExecutionStartTime.set(now);
  }
check if there is tmp file to be deleted.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/execution/fragment/FragmentInstanceContext.java