Cleanup pipeline build stage background migration

db/migrate/20180420010616_cleanup_build_stage_migration.rb

+class CleanupBuildStageMigration < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  class Build < ActiveRecord::Base
+    include EachBatch
+
+    self.table_name = 'ci_builds'
+    self.inheritance_column = :_type_disabled
+  end
+
+  def up
+    Gitlab::BackgroundMigration.steal('MigrateBuildStage')
+
+    Build.where('stage_id IS NULL').each_batch(of: 50) do |batch|
+      range = batch.pluck('MIN(id)', 'MAX(id)').first
+
+      Gitlab::BackgroundMigration::MigrateBuildStage.new.perform(*range)
+    end
+  end
+
+  def down
+    # noop
+  end
+end

spec/migrations/cleanup_build_stage_migration_spec.rb

+require 'spec_helper'
+require Rails.root.join('db', 'migrate', '20180420010616_cleanup_build_stage_migration.rb')
+
+describe CleanupBuildStageMigration, :migration, :sidekiq, :redis do
+  let(:migration) { spy('migration') }
+
+  before do
+    allow(Gitlab::BackgroundMigration::MigrateBuildStage)
+      .to receive(:new).and_return(migration)
+  end
+
+  context 'when there are pending background migrations' do
+    it 'processes pending jobs synchronously' do
+      Sidekiq::Testing.disable! do
+        BackgroundMigrationWorker
+          .perform_in(2.minutes, 'MigrateBuildStage', [1, 1])
+        BackgroundMigrationWorker
+          .perform_async('MigrateBuildStage', [1, 1])
+
+        migrate!
+
+        expect(migration).to have_received(:perform).with(1, 1).twice
+      end
+    end
+  end
+
+  context 'when there are no background migrations pending' do
+    it 'does nothing' do
+      Sidekiq::Testing.disable! do
+        migrate!
+
+        expect(migration).not_to have_received(:perform)
+      end
+    end
+  end
+
+  context 'when there are still unmigrated builds present' do
+    let(:builds) { table('ci_builds') }
+
+    before do
+      builds.create!(name: 'test:1', ref: 'master')
+      builds.create!(name: 'test:2', ref: 'master')
+    end
+
+    it 'migrates stages sequentially in batches' do
+      expect(builds.all).to all(have_attributes(stage_id: nil))
+
+      migrate!
+
+      expect(migration).to have_received(:perform).once
+    end
+  end
+end