Convert ci_builds-runner_id FK to LFK

Some runner_ids may be assigned to too many ci_builds so that deleting
them can cause downtime in the DB. So, we decided to convert this FK
to LFK.

Changelog: other

config/gitlab_loose_foreign_keys.yml

@@ -11,6 +11,9 @@ ci_builds:
   - table: projects
     column: project_id
     on_delete: async_delete
+  - table: ci_runners
+    column: runner_id
+    on_delete: async_nullify
 ci_builds_metadata:
   - table: projects
     column: project_id

db/post_migrate/20220317161914_remove_ci_runners_ci_builds_runner_id_fk.rb

+# frozen_string_literal: true
+
+class RemoveCiRunnersCiBuildsRunnerIdFk < Gitlab::Database::Migration[1.0]
+  disable_ddl_transaction!
+
+  def up
+    return unless foreign_key_exists?(:ci_builds, :ci_runners, name: "fk_e4ef9c2f27")
+
+    with_lock_retries do
+      execute('LOCK ci_runners, ci_builds IN ACCESS EXCLUSIVE MODE') if transaction_open?
+
+      remove_foreign_key_if_exists(:ci_builds, :ci_runners, name: "fk_e4ef9c2f27")
+    end
+  end
+
+  def down
+    add_concurrent_foreign_key :ci_builds, :ci_runners, name: "fk_e4ef9c2f27", column: :runner_id, target_column: :id, on_delete: :nullify, validate: false
+  end
+end

db/schema_migrations/20220317161914

+94a8bc74fc935ba863d22b59b0ac6808bf5a9714c3759ca75a6dbee50c3c647d
\ No newline at end of file

db/structure.sql

@@ -31696,9 +31696,6 @@ ALTER TABLE ONLY ci_builds_metadata
 ALTER TABLE ONLY gitlab_subscriptions
     ADD CONSTRAINT fk_e2595d00a1 FOREIGN KEY (namespace_id) REFERENCES namespaces(id) ON DELETE CASCADE;
 
-ALTER TABLE ONLY ci_builds
-    ADD CONSTRAINT fk_e4ef9c2f27 FOREIGN KEY (runner_id) REFERENCES ci_runners(id) ON DELETE SET NULL NOT VALID;
-
 ALTER TABLE ONLY merge_requests
     ADD CONSTRAINT fk_e719a85f8a FOREIGN KEY (author_id) REFERENCES users(id) ON DELETE SET NULL;
 

spec/models/commit_status_spec.rb

@@ -994,4 +994,11 @@ RSpec.describe CommitStatus do
       let!(:model) { create(:ci_build, project: parent) }
     end
   end
+
+  context 'loose foreign key on ci_builds.runner_id' do
+    it_behaves_like 'cleanup by a loose foreign key' do
+      let!(:parent) { create(:ci_runner) }
+      let!(:model) { create(:ci_build, runner: parent) }
+    end
+  end
 end