Support multiple databases for batched background migrations

- Add an option to disable the batched background migrations worker
  via feature flag for CI and Main database

Changelog: added

Relates to https://gitlab.com/gitlab-org/gitlab/-/merge_requests/83109

app/workers/database/batched_background_migration/ci_database_worker.rb

@@ -4,6 +4,10 @@ module Database
     class CiDatabaseWorker # rubocop:disable Scalability/IdempotentWorker
       include SingleDatabaseWorker
 
+      def self.enabled?
+        Feature.enabled?(:execute_batched_migrations_on_schedule_ci_database, type: :ops, default_enabled: :yaml)
+      end
+
       def self.tracking_database
         @tracking_database ||= Gitlab::Database::CI_DATABASE_NAME
       end

app/workers/database/batched_background_migration/single_database_worker.rb

@@ -23,6 +23,10 @@ module Database
         def tracking_database
           raise NotImplementedError, "#{self.name} does not implement #{__method__}"
         end
+
+        def enabled?
+          raise NotImplementedError, "#{self.name} does not implement #{__method__}"
+        end
         # :nocov:
 
         def lease_key
@@ -41,7 +45,7 @@ module Database
         end
 
         Gitlab::Database::SharedModel.using_connection(base_model.connection) do
-          break unless Feature.enabled?(:execute_batched_migrations_on_schedule, type: :ops, default_enabled: :yaml) && active_migration
+          break unless self.class.enabled? && active_migration
 
           with_exclusive_lease(active_migration.interval) do
             # Now that we have the exclusive lease, reload migration in case another process has changed it.

app/workers/database/batched_background_migration_worker.rb

@@ -4,6 +4,10 @@ module Database
   class BatchedBackgroundMigrationWorker # rubocop:disable Scalability/IdempotentWorker
     include BatchedBackgroundMigration::SingleDatabaseWorker
 
+    def self.enabled?
+      Feature.enabled?(:execute_batched_migrations_on_schedule, type: :ops, default_enabled: :yaml)
+    end
+
     def self.tracking_database
       @tracking_database ||= Gitlab::Database::MAIN_DATABASE_NAME.to_sym
     end

config/feature_flags/ops/execute_batched_migrations_on_schedule_ci_database.yml

+---
+name: execute_batched_migrations_on_schedule_ci_database
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/83109
+rollout_issue_url:
+milestone: '14.9'
+type: ops
+group: group::database
+default_enabled: false

spec/support/shared_examples/workers/batched_background_migration_worker_shared_examples.rb

 # frozen_string_literal: true
 
-RSpec.shared_examples 'it runs batched background migration jobs' do |tracking_database|
+RSpec.shared_examples 'it runs batched background migration jobs' do |tracking_database, feature_flag:|
   include ExclusiveLeaseHelpers
 
   describe 'defining the job attributes' do
@@ -39,6 +39,16 @@ RSpec.shared_examples 'it runs batched background migration jobs' do |tracking_d
     end
   end
 
+  describe '.enabled?' do
+    it 'does not raise an error' do
+      expect { described_class.enabled? }.not_to raise_error
+    end
+
+    it 'returns true' do
+      expect(described_class.enabled?).to be_truthy
+    end
+  end
+
   describe '#perform' do
     subject(:worker) { described_class.new }
 
@@ -76,7 +86,7 @@ RSpec.shared_examples 'it runs batched background migration jobs' do |tracking_d
 
       context 'when the feature flag is disabled' do
         before do
-          stub_feature_flags(execute_batched_migrations_on_schedule: false)
+          stub_feature_flags(feature_flag => false)
         end
 
         it 'does nothing' do
@@ -89,7 +99,7 @@ RSpec.shared_examples 'it runs batched background migration jobs' do |tracking_d
 
       context 'when the feature flag is enabled' do
         before do
-          stub_feature_flags(execute_batched_migrations_on_schedule: true)
+          stub_feature_flags(feature_flag => true)
 
           allow(Gitlab::Database::BackgroundMigration::BatchedMigration).to receive(:active_migration).and_return(nil)
         end

spec/workers/database/batched_background_migration/ci_database_worker_spec.rb

@@ -3,5 +3,5 @@
 require 'spec_helper'
 
 RSpec.describe Database::BatchedBackgroundMigration::CiDatabaseWorker, :clean_gitlab_redis_shared_state do
-  it_behaves_like 'it runs batched background migration jobs', 'ci'
+  it_behaves_like 'it runs batched background migration jobs', 'ci', feature_flag: :execute_batched_migrations_on_schedule_ci_database
 end

spec/workers/database/batched_background_migration_worker_spec.rb

@@ -3,5 +3,5 @@
 require 'spec_helper'
 
 RSpec.describe Database::BatchedBackgroundMigrationWorker do
-  it_behaves_like 'it runs batched background migration jobs', :main
+  it_behaves_like 'it runs batched background migration jobs', :main, feature_flag: :execute_batched_migrations_on_schedule
 end