Remove merge_request_refresh_batched_commit_lookup feature flag

Marc Shawrequested to merge
608174-remove-merge-request-refresh-batched-commit-lookup-ff into master

What does this MR do and why?

This MR removes the merge_request_refresh_batched_commit_lookup feature flag and keeps the batched code path permanently. The flag has been fully enabled on production since 2026-08-26 with no regressions, so the old per-merge-request lookup path can be deleted.

Detailed context for AI agents

Background:

  • Flag type: beta, default_enabled: true, introduced in milestone 19.3, actor: project.
  • Introduced by !248701 (merged) (merged 2026-08-19) as corrective action for production incident gitlab-com/gl-infra/production#22645 (closed), where large mirror pushes ran UpdateMergeRequestsWorker for 5-10 hours.
  • Rollout history on production: 25% of actors on 2026-08-21, 50% on 2026-08-25, 100% / fully enabled on 2026-08-26. No regressions or incidents reported since.

What the flag controlled: In MergeRequests::RefreshService#reload_merge_requests, on every push the service decides which open merge requests targeting the pushed branch need their diff reloaded (the "stacked" case - a merge request whose diff already contains one of the pushed commits).

  • Old path: asked each merge request individually via MergeRequestDiff#includes_any_commits?. Query count scaled with merge request count x push size.
  • New path: resolves the whole set in one query per 1,000-commit chunk via MergeRequestDiff.ids_including_any_commits.

Code changes:

  • app/services/merge_requests/refresh_service.rb: removed the Feature.enabled? gate and batched_commit_lookup_enabled?, deleted old_recheck_merge_requests_batched, renamed new_recheck_merge_requests_batched to recheck_merge_requests_batched. The service now always takes the batched path.
  • app/models/merge_request_diff.rb: removed #includes_any_commits? and the private #metadata_sha_exists?, since the old refresh path was their only caller. Reworded the comment on .ids_including_any_commits, which referred to the removed method.
  • config/feature_flags/beta/merge_request_refresh_batched_commit_lookup.yml: deleted.
  • spec/models/merge_request_diff_spec.rb: removed the #includes_any_commits? describe block.
  • spec/services/merge_requests/refresh_service_spec.rb: removed the two "feature flag is disabled" contexts.
  • spec/support/matchers/query_missing_diff_commit_columns.rb: updated the example in the header comment to use ids_including_any_commits instead of the removed method.

Confirmed no other callers of the removed methods exist in app, lib, ee, spec, or qa.

Verification performed:

  • Rubocop on all changed files: no offenses.
  • bundle exec rspec spec/services/merge_requests/refresh_service_spec.rb: 102 examples, 0 failures.
  • bundle exec rspec spec/models/merge_request_diff_spec.rb: 384 examples, 0 failures.

Rollback consideration: there is no old code path left in this MR, so reverting the flag behaviour would mean reverting this MR itself. The batched path has run at 100% on production since 2026-08-26.

Follow-up after merge: delete the flag from all environments with /chatops run feature delete merge_request_refresh_batched_commit_lookup --dev --pre --staging --staging-ref --production.

Commit uses Changelog: other, since this removes a default-on flag while keeping the feature itself unchanged.

References

Screenshots or screen recordings

Not applicable, backend-only change with no UI.

How to set up and validate locally

  1. Checkout this branch and run bundle install if needed.
  2. Run bundle exec rspec spec/services/merge_requests/refresh_service_spec.rb and confirm all examples pass.
  3. Run bundle exec rspec spec/models/merge_request_diff_spec.rb and confirm all examples pass.
  4. Optionally, in GDK: open a merge request targeting a branch, push a new commit to that branch, and confirm the merge request's diff reloads (the merge_request_diffs count increases) with a single ids_including_any_commits query for the push.

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