Schedule artifact expiry backfill again

The previous background migration left around 400.000 artifacts without
an expiry date. This schedules the background migration again to
backfill those entries as well.

changelogs/unreleased/mc-backstage-reschedule-artifac-expiry-date-again.yml

+---
+title: Schedule artifact expiry backfill again.
+merge_request: 59270
+author:
+type: changed

db/post_migrate/20210413132500_reschedule_artifact_expiry_backfill_again.rb

+# frozen_string_literal: true
+
+class RescheduleArtifactExpiryBackfillAgain < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  MIGRATION = 'BackfillArtifactExpiryDate'
+  SWITCH_DATE = Date.new(2020, 06, 22).freeze
+
+  disable_ddl_transaction!
+
+  class JobArtifact < ActiveRecord::Base
+    include EachBatch
+
+    self.inheritance_column = :_type_disabled
+    self.table_name = 'ci_job_artifacts'
+
+    scope :without_expiry_date, -> { where(expire_at: nil) }
+    scope :before_switch, -> { where("date(created_at AT TIME ZONE 'UTC') < ?::date", SWITCH_DATE) }
+  end
+
+  def up
+    Gitlab::BackgroundMigration.steal(MIGRATION) do |job|
+      job.delete
+
+      false
+    end
+
+    queue_background_migration_jobs_by_range_at_intervals(
+      JobArtifact.without_expiry_date.before_switch,
+      MIGRATION,
+      2.minutes,
+      batch_size: 200_000
+    )
+  end
+
+  def down
+    Gitlab::BackgroundMigration.steal(MIGRATION) do |job|
+      job.delete
+
+      false
+    end
+  end
+end

db/schema_migrations/20210413132500

+407806cc168ef9859c9a4f1bd4db7a56aee01367e784ea0767889863b9ace35d
\ No newline at end of file

spec/migrations/20210413132500_reschedule_artifact_expiry_backfill_again_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+require Rails.root.join('db', 'post_migrate', '20210413132500_reschedule_artifact_expiry_backfill_again.rb')
+
+RSpec.describe RescheduleArtifactExpiryBackfillAgain, :migration do
+  let(:migration_class) { Gitlab::BackgroundMigration::BackfillArtifactExpiryDate }
+  let(:migration_name)  { migration_class.to_s.demodulize }
+
+  before do
+    table(:namespaces).create!(id: 123, name: 'test_namespace', path: 'test_namespace')
+    table(:projects).create!(id: 123, name: 'sample_project', path: 'sample_project', namespace_id: 123)
+  end
+
+  it 'correctly schedules background migrations' do
+    first_artifact = create_artifact(job_id: 0, expire_at: nil, created_at: Date.new(2020, 06, 21))
+    second_artifact = create_artifact(job_id: 1, expire_at: nil, created_at: Date.new(2020, 06, 21))
+    create_artifact(job_id: 2, expire_at: Date.yesterday, created_at: Date.new(2020, 06, 21))
+    create_artifact(job_id: 3, expire_at: nil, created_at: Date.new(2020, 06, 23))
+
+    Sidekiq::Testing.fake! do
+      freeze_time do
+        migrate!
+
+        expect(BackgroundMigrationWorker.jobs.size).to eq(1)
+        expect(migration_name).to be_scheduled_migration_with_multiple_args(first_artifact.id, second_artifact.id)
+      end
+    end
+  end
+
+  private
+
+  def create_artifact(params)
+    table(:ci_builds).create!(id: params[:job_id], project_id: 123)
+    table(:ci_job_artifacts).create!(project_id: 123, file_type: 1, **params)
+  end
+end