code: public void setMaxBatchDeleteSize(int size) {
      Preconditions.checkArgument(size > 0, "size should be positive, got" + size);
      Preconditions.checkArgument(size <= DEFAULT_MAX_BATCH_DELETE_SIZE,
          "size should <= " + DEFAULT_MAX_BATCH_DELETE_SIZE + " got " + size);
      this.batchDeleteSize = size;
    }
docs: Set items deleted each round in deleteObjects, if more than
  $size object left, deleteObjects will delete them in several
  rounds internally.
  @param size positive and greater than DEFAULT_MAX_BATCH_DELETE_SIZE,