Mark completed jobs as successful

This is essentially the same as spec/lib/gitlab/background_migration/backfill_draft_status_on_merge_requests_spec.rb
but with the newly-added helper to mark track_jobs as completed (per
@sabrams in
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/66788#note_644449984)

Changelog: added

db/post_migrate/20210806011811_schedule_backfill_draft_column_on_merge_requests_rerun.rb

+# frozen_string_literal: true
+
+class ScheduleBackfillDraftColumnOnMergeRequestsRerun < ActiveRecord::Migration[6.1]
+  include Gitlab::Database::MigrationHelpers
+
+  MIGRATION = 'BackfillDraftStatusOnMergeRequests'
+  DELAY_INTERVAL = 2.minutes
+  BATCH_SIZE = 50
+
+  disable_ddl_transaction!
+
+  def up
+    eligible_mrs = Gitlab::BackgroundMigration::BackfillDraftStatusOnMergeRequests::MergeRequest.eligible
+
+    queue_background_migration_jobs_by_range_at_intervals(
+      eligible_mrs,
+      MIGRATION,
+      DELAY_INTERVAL,
+      track_jobs: true,
+      batch_size: BATCH_SIZE
+    )
+  end
+
+  def down
+    # noop
+    #
+  end
+end

db/schema_migrations/20210806011811

+e4f4f3c91cdb8ce8b1fa6c2bd0bb1fb1a8c0dedbb78c20bbaef6e36bfa9551c4
\ No newline at end of file

lib/gitlab/background_migration/backfill_draft_status_on_merge_requests.rb

@@ -27,6 +27,17 @@ module Gitlab
         eligible_mrs.each_slice(10) do |slice|
           MergeRequest.where(id: slice).update_all(draft: true)
         end
+
+        mark_job_as_succeeded(start_id, end_id)
+      end
+
+      private
+
+      def mark_job_as_succeeded(*arguments)
+        Gitlab::Database::BackgroundMigrationJob.mark_all_as_succeeded(
+          'BackfillDraftStatusOnMergeRequests',
+          arguments
+        )
       end
     end
   end

spec/lib/gitlab/background_migration/backfill_draft_status_on_merge_requests_spec.rb

@@ -23,6 +23,8 @@ RSpec.describe Gitlab::BackgroundMigration::BackfillDraftStatusOnMergeRequests d
   end
 
   context "for MRs with #draft? == true titles but draft attribute false" do
+    let(:mr_ids) { merge_requests.all.collect(&:id) }
+
     before do
       draft_prefixes.each do |prefix|
         (1..4).each do |n|
@@ -37,11 +39,16 @@ RSpec.describe Gitlab::BackgroundMigration::BackfillDraftStatusOnMergeRequests d
 
     it "updates all open draft merge request's draft field to true" do
       mr_count = merge_requests.all.count
-      mr_ids = merge_requests.all.collect(&:id)
 
       expect { subject.perform(mr_ids.first, mr_ids.last) }
         .to change { MergeRequest.where(draft: false).count }
         .from(mr_count).to(mr_count - draft_prefixes.length)
     end
+
+    it "marks successful slices as completed" do
+      expect(subject).to receive(:mark_job_as_succeeded).with(mr_ids.first, mr_ids.last)
+
+      subject.perform(mr_ids.first, mr_ids.last)
+    end
   end
 end