<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=18705) </details> <!--IssueSummary end--> Originally, `merge_request_diff_commits` was meant to have three columns: 1. `merge_request_diff_id` 2. `relative_order` 3. `sha` However, for simplicity, I added columns representing almost all of the fields we serialised in `st_commits`. The only exception was `parent_ids`, as it appeared to be unused. We should try to find which other columns are unused and remove those, until we're left with the original three. Commit metadata for an MR diff can come from its `Compare` object, with a fallback if there are old MR diffs without commits kept around in the repo. This is currently blocked by https://gitlab.com/gitlab-org/gitlab-ce/issues/34743.