Add a worker to run the partition detach workflow

This worker runs `PartitionManager.detach_partitions` on a schedule to
trigger the detach logic for old database partitions that are no longer
needed

app/workers/all_queues.yml

@@ -247,6 +247,15 @@
   :idempotent: true
   :tags:
   - :exclude_from_kubernetes
+- :name: cronjob:database_partition_detach
+  :worker_name: Database::PartitionDetachWorker
+  :feature_category: :database
+  :has_external_dependencies:
+  :urgency: :low
+  :resource_boundary: :unknown
+  :weight: 1
+  :idempotent: true
+  :tags: []
 - :name: cronjob:environments_auto_stop_cron
   :worker_name: Environments::AutoStopCronWorker
   :feature_category: :continuous_delivery

app/workers/database/partition_detach_worker.rb

+# frozen_string_literal: true
+
+module Database
+  class PartitionDetachWorker
+    include ApplicationWorker
+
+    sidekiq_options retry: 3
+    include CronjobQueue # rubocop:disable Scalability/CronWorkerContext
+
+    feature_category :database
+    idempotent!
+
+    def perform
+      Gitlab::Database::Partitioning::PartitionManager.new.detach_partitions
+    ensure
+      Gitlab::Database::Partitioning::PartitionMonitoring.new.report_metrics
+    end
+  end
+end

config/initializers/1_settings.rb

@@ -543,6 +543,9 @@ Settings.cron_jobs['update_container_registry_info_worker']['job_class'] = 'Upda
 Settings.cron_jobs['postgres_dynamic_partitions_creator'] ||= Settingslogic.new({})
 Settings.cron_jobs['postgres_dynamic_partitions_creator']['cron'] ||= '21 */6 * * *'
 Settings.cron_jobs['postgres_dynamic_partitions_creator']['job_class'] ||= 'PartitionCreationWorker'
+Settings.cron_jobs['postgres_dynamic_partitions_detacher'] ||= Settingslogic.new({})
+Settings.cron_jobs['postgres_dynamic_partitions_detacher']['cron'] ||= '25 */6 * * *'
+Settings.cron_jobs['postgres_dynamic_partitions_detacher']['job_class'] ||= 'Database::PartitionDetachWorker'
 Settings.cron_jobs['ci_platform_metrics_update_cron_worker'] ||= Settingslogic.new({})
 Settings.cron_jobs['ci_platform_metrics_update_cron_worker']['cron'] ||= '47 9 * * *'
 Settings.cron_jobs['ci_platform_metrics_update_cron_worker']['job_class'] = 'CiPlatformMetricsUpdateCronWorker'

spec/workers/database/partition_detach_worker_spec.rb

+# frozen_string_literal: true
+
+require "spec_helper"
+
+RSpec.describe Database::PartitionDetachWorker do
+  describe '#perform' do
+    subject { described_class.new.perform }
+
+    let(:manager) {  instance_double('PartitionManager', detach_partitions: nil) }
+    let(:monitoring) { instance_double('PartitionMonitoring', report_metrics: nil) }
+
+    before do
+      allow(Gitlab::Database::Partitioning::PartitionManager).to receive(:new).and_return(manager)
+      allow(Gitlab::Database::Partitioning::PartitionMonitoring).to receive(:new).and_return(monitoring)
+    end
+
+    it 'delegates to PartitionManager' do
+      expect(manager).to receive(:detach_partitions)
+
+      subject
+    end
+
+    it 'reports partition metrics' do
+      expect(monitoring).to receive(:report_metrics)
+
+      subject
+    end
+  end
+end