Make sure all stages are migrated after a cleanup

db/migrate/20170912113435_clean_stages_statuses_migration.rb

@@ -5,8 +5,19 @@ class CleanStagesStatusesMigration < ActiveRecord::Migration
 
   disable_ddl_transaction!
 
+  class Stage < ActiveRecord::Base
+    include ::EachBatch
+    self.table_name = 'ci_stages'
+  end
+
   def up
     Gitlab::BackgroundMigration.steal('MigrateStageStatus')
+
+    Stage.where('status IS NULL').each_batch(of: 50) do |batch|
+      range = batch.pluck('MIN(id)', 'MAX(id)').first
+
+      Gitlab::BackgroundMigration::MigrateStageStatus.new.perform(*range)
+    end
   end
 
   def down

spec/migrations/clean_stages_statuses_migration_spec.rb

@@ -23,6 +23,7 @@ describe CleanStagesStatusesMigration, :migration, :sidekiq, :redis do
       end
     end
   end
+
   context 'when there are no background migrations pending' do
     it 'does nothing' do
       Sidekiq::Testing.disable! do
@@ -32,4 +33,19 @@ describe CleanStagesStatusesMigration, :migration, :sidekiq, :redis do
       end
     end
   end
+
+  context 'when there are still unmigrated stages afterwards' do
+    let(:stages) { table('ci_stages') }
+
+    before do
+      stages.create!(status: nil, name: 'build')
+      stages.create!(status: nil, name: 'test')
+    end
+
+    it 'migrates statuses sequentially in batches' do
+      migrate!
+
+      expect(migration).to have_received(:perform).once
+    end
+  end
 end