Add cr remarks

db/post_migrate/20201104124300_ensure_namespace_settings_creation.rb

 # frozen_string_literal: true
 
 class EnsureNamespaceSettingsCreation < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
   DOWNTIME = false
   BATCH_SIZE = 10000
+  MIGRATION = 'BackfillNamespaceSettings'
+  DELAY_INTERVAL = 2.minutes.to_i
+
+  disable_ddl_transaction!
 
   class Namespace < ActiveRecord::Base
     include EachBatch
@@ -21,12 +27,13 @@ class EnsureNamespaceSettingsCreation < ActiveRecord::Migration[5.2]
   private
 
   def ensure_data_migration
-    Namespace.each_batch(of: BATCH_SIZE) do |query|
+    Namespace.each_batch(of: BATCH_SIZE) do |query, index|
       missing_count = query.where("NOT EXISTS (SELECT 1 FROM namespace_settings WHERE namespace_settings.namespace_id=namespaces.id)").limit(1).size
+
       if missing_count > 0
-        min, max = query.pluck("MIN(id), MAX(id)").flatten
-        # we expect low record count so inline execution is fine.
-        Gitlab::BackgroundMigration::BackfillNamespaceSettings.new.perform(min, max)
+        ids_range = query.pluck("MIN(id), MAX(id)").flatten
+
+        migrate_in(index * DELAY_INTERVAL, MIGRATION, ids_range)
       end
     end
   end

spec/migrations/ensure_namespace_settings_creation_spec.rb

@@ -8,9 +8,37 @@ RSpec.describe EnsureNamespaceSettingsCreation do
     let(:namespaces) { table(:namespaces) }
     let(:namespace_settings) { table(:namespace_settings) }
     let!(:namespace) { namespaces.create!(name: 'gitlab', path: 'gitlab-org') }
+    let!(:namespace_2) { namespaces.create!(name: 'gitlab', path: 'gitlab-org2') }
 
     it 'migrates namespaces without namespace_settings' do
-      expect { migrate! }.to change { namespace_settings.count }.from(0).to(1)
+      stub_const("#{described_class.name}::BATCH_SIZE", 2)
+
+      Sidekiq::Testing.fake! do
+        freeze_time do
+          migrate!
+
+          expect(described_class::MIGRATION)
+            .to be_scheduled_delayed_migration(2.minutes.to_i, namespace.id, namespace_2.id)
+        end
+      end
+    end
+
+    it 'schedules migrations in batches ' do
+      stub_const("#{described_class.name}::BATCH_SIZE", 2)
+
+      namespace_3 = namespaces.create!(name: 'gitlab', path: 'gitlab-org3')
+      namespace_4 = namespaces.create!(name: 'gitlab', path: 'gitlab-org4')
+
+      Sidekiq::Testing.fake! do
+        freeze_time do
+          migrate!
+
+          expect(described_class::MIGRATION)
+            .to be_scheduled_delayed_migration(2.minutes.to_i, namespace.id, namespace_2.id)
+          expect(described_class::MIGRATION)
+            .to be_scheduled_delayed_migration(4.minutes.to_i, namespace_3.id, namespace_4.id)
+        end
+      end
     end
   end
 end