code: func NewDeleteRangeTask(ctx context.Context, store Storage, startKey []byte, endKey []byte) *DeleteRangeTask {
  	return &DeleteRangeTask{
  		completedRegions: 0,
  		canceled:         false,
  		store:            store,
  		ctx:              ctx,
  		startKey:         startKey,
  		endKey:           endKey,
  	}
  }
docs: // NewDeleteRangeTask creates a DeleteRangeTask. Deleting will not be performed right away.
  // WARNING: Currently, this API may leave some waste key-value pairs uncleaned in TiKV. Be careful while using it.