What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind bug

What does this PR do / why do we need it:

  1. fix concat get_dataset_size error
  2. update api comment

Which issue(s) this PR fixes:

Fixes #I1RO24
Fixes #I1RU13

Special notes for your reviewers:
None