code: func (e *IndexLookUpJoin) Close() error {
  	if e.cancelFunc != nil {
  		e.cancelFunc()
  	}
  	e.workerWg.Wait()
  	e.memTracker.Detach()
  	e.memTracker = nil
  	return e.children[0].Close()
  }
docs: // Close implements the Executor interface.