When a user merges a merge request, the following sequence happens:

1. Sidekiq: `MergeService` locks the state of the merge request in the
DB.
2. Gitaly: UserMergeBranch RPC runs and creates a merge commit.
3. Sidekiq: `Repository#merge` and `Repository#ff_merge` updates the
   `in_progress_merge_commit_sha` database column with this merge commit
   SHA.
4. Gitaly: UserMergeBranch RPC runs again and applies this merge commit
to the target branch.
5. Gitaly (gitaly-ruby): This RPC calls the pre-receive hook.
6. Rails: This hook makes an API request to `/api/v4/internal/allowed`.
7. Rails: This API check makes a SQL query for locked merge requests
   with a matching SHA.

Since steps 1 and 7 will happen in different database sessions,
replication lag could erroneously cause step 7 to report no matching
merge requests. To avoid this, we have a few options:

1. Wrap step 7 in a transaction. The EE load balancer will always
   direct these queries to the primary.
2. Always force the load balancer session to use the primary for this
   query.
3. Use the load balancing sticking mechanism to use the primary until
   the secondaries have caught up to the right write location.

Option 1 isn't great because on GitLab.com, this query can take 500 ms
to run, and long-running, read transactions are not desirable.

Option 2 is simple and guarantees that we will always have a consistent
read. However, none of these queries will ever be routed to a secondary,
and this may cause undo load on the primary.

We go with option 3. Whenever the `in_progress_merge_commit_sha` is
updated, we mark the write location of the primary. Then in
`MatchingMergeRequest#match?`, we stick to the primary if the replica
has not caught up to that location.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/247857

Remove unused constant

See merge request gitlab-org/gitlab!42603

Added standard terms for UI navigation

Closes technical-writing#100

See merge request gitlab-org/gitlab!42557

Screenshot update to remove 'new' per UI update

Closes #216928

See merge request gitlab-org/gitlab!42898

The `MAXIMUM_FILE_SIZE` usage was removed with
https://gitlab.com/gitlab-org/gitlab/-/commit/12138d7e126c823521fa637a72fcf5771c7e1002,
but the constant was not deleted. This commit removes it.

Add system note on change incidents severity

See merge request gitlab-org/gitlab!42358

Merge branch '241955-remove-v-html-from-app-assets-javascripts-diffs-components-diff_file_header-vue' into 'master'

Remove v-html from app/assets/javascripts/diffs/components/diff_file_header.vue

Closes #241955

See merge request gitlab-org/gitlab!41483

Docs style: Changed "click" to "select"

See merge request gitlab-org/gitlab!42741

Add swimlanes to premium license

See merge request gitlab-org/gitlab!41543

Fix `hot-reloading` of feature flag definitions

See merge request gitlab-org/gitlab!42876

Update Gitaly version

See merge request gitlab-org/gitlab!42883

Update button to gl-button on GitLab for Slack page

Closes #229329

See merge request gitlab-org/gitlab!42426

Merge branch '241926-remove-v-html-from-app-assets-javascripts-releases-components-app_edit_new-vue' into 'master'

Replace v-html with gl-sprintf in app/assets/javascripts/releases/components/app_edit_new.vue

Closes #241926

See merge request gitlab-org/gitlab!41508

Add Merge Request CSV export service

See merge request gitlab-org/gitlab!42241

Update Gitaly version

See merge request gitlab-org/gitlab!42875

Merge branch '249316-make-gitlab-ci-file-visualization-works-with-files-extenstion-other-than-gitlab-ci-yml' into 'master'

Make yaml viz works with extensions other than .gitlab-ci.yml

Closes #249316

See merge request gitlab-org/gitlab!42632

Instead of relying on a regexp in the frontend which
is a flakier and also doesn't consider that we can
have custom gitlab-ci names, this is in sync with
the API to determine that we are editing a config
file.

Add the `blob:` search filter to search by Git object-id

Closes #251223

See merge request gitlab-org/gitlab!42752

It appears that during `hot-reload` there is very
often the race condition: class gets loaded,
but we cannot properly trigger `load_all!`
before code might be interested in checking feature flag
state

There's also one missing `type: :ops` for supporting `sidekiq`

Docs: Update feature tables info for clarity

See merge request gitlab-org/gitlab!42744

Document Geo PG12 upgrade test results

See merge request gitlab-org/gitlab!42737

Add seed project issue to Geo troubleshooting docs

See merge request gitlab-org/gitlab!42755

Recommend telemetry review

See merge request gitlab-org/gitlab!42856

Docs: Update "to do item" wording

See merge request gitlab-org/gitlab!42724

[ci skip]

[ci skip]

Reformat bitbucket server feature flag info

Closes #249363

See merge request gitlab-org/gitlab!42766

Migrate haml button to our utility classes

See merge request gitlab-org/gitlab!42676

Assign reviews to hungry reviewers first

Closes #243712

See merge request gitlab-org/gitlab!41938

This causes Reviewer Roulette to suggest reviewers with a "hungry"
status instead of other reviewers.