to better reflect the status. Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/7508#note_18858398

* Introduce `HasStatus.cancelable` which we might be able to cancel
* Cancel and check upon `cancelable`
* Also cancel on `CommitStatus` rather than just `Ci::Build`

Fixes #23635

Fixes #17845

They were Rails' default and are unnecessarily overridden.
Signed-off-by: David Wagner <david@marvid.fr>

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6342#note_17089690

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6342/diffs#note_17039533

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6342/diffs#note_17038749

Closes #23326

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6342#note_16956937

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6342#note_16118195

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6342#note_16073734

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6342#note_16074432

This reverts commit 1404aa86.

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6019#note_16963209

Feedback:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6019#note_16956802

Conflicts:
	app/models/ci/pipeline.rb
	app/models/commit_status.rb

which merges previous exclude_ignored_jobs and failed_but_allowed,
so that we don't treat ignored a special case in HasStatus.

1. Change multiple updates to a single `update_all`

2. Use cascading deletes

3. Extract an average function for the database median.

4. Move database median to `lib/gitlab/database`

5. Use `delete_all` instead of `destroy_all`

6. Minor refactoring

This solves Pipelines in `running` after all stages do finish.

All the code that pre-calculates metrics for use in the cycle analytics
page.

- Ci::Pipeline -> build start/finish
- Ci::Pipeline#merge_requests
- Issue -> record default metrics after save
- MergeRequest -> record default metrics after save
- Deployment -> Update "first_deployed_to_production_at" for MR metrics
- Git Push -> Update "first commit mention" for issue metrics
- Merge request create/update/refresh -> Update "merge requests closing issues"

Better import of labels, milestones and protected branches. Updated relevant specs.
Loose pipeline validation on importing, so it does not fail when there are missing fields, which are not validated at DB level. Also, updated spec with relevant test.

1. These changes bring down page load time for 100 issues from more than
   a minute to about 1.5 seconds.

2. This entire commit is composed of these types of performance
   enhancements:

     - Cache relevant data in `IssueMetrics` wherever possible.
     - Cache relevant data in `MergeRequestMetrics` wherever possible.
     - Preload metrics

3. Given these improvements, we now only need to make 4 SQL calls:

    - Load all issues
    - Load all merge requests
    - Load all metrics for the issues
    - Load all metrics for the merge requests

4. A list of all the data points that are now being pre-calculated:

    a. The first time an issue is mentioned in a commit

      - In `GitPushService`, find all issues mentioned by the given commit
        using `ReferenceExtractor`. Set the `first_mentioned_in_commit_at`
        flag for each of them.

      - There seems to be a (pre-existing) bug here - files (and
        therefore commits) created using the Web CI don't have
        cross-references created, and issues are not closed even when
        the commit title is "Fixes #xx".

    b. The first time a merge request is deployed to production

      When a `Deployment` is created, find all merge requests that
      were merged in before the deployment, and set the
      `first_deployed_to_production_at` flag for each of them.

    c. The start / end time for a merge request pipeline

      Hook into the `Pipeline` state machine. When the `status` moves to
      `running`, find the merge requests whose tip commit matches the
      pipeline, and record the `latest_build_started_at` time for each
      of them. When the `status` moves to `success`, record the
      `latest_build_finished_at` time.

    d. The merge requests that close an issue

      - This was a big cause of the performance problems we were having
        with Cycle Analytics. We need to use `ReferenceExtractor` to make
        this calculation, which is slow when we have to run it on a large
        number of merge requests.

      - When a merge request is created, updated, or refreshed, find the
        issues it closes, and create an instance of
        `MergeRequestsClosingIssues`, which acts as a join model between
        merge requests and issues.

      - If a `MergeRequestsClosingIssues` instance links a merge request
        and an issue, that issue closes that merge request.

5. The `Queries` module was changed into a class, so we can cache the
   results of `issues` and `merge_requests_closing_issues` across
   various cycle analytics stages.

6. The code added in this commit is untested. Tests will be added in the
   next commit.

Closes #19804

retries and probably also manual actions!

Feedback:

* https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6084#note_14735478
* https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6084#note_14737804