Make patch prometheus migration no-op

Due to lack of right revert strategy for
background migrations it was decided to
turn this migrations in to no-op

db/post_migrate/20191220102807_patch_prometheus_services_for_shared_cluster_applications.rb

@@ -54,25 +54,6 @@ class PatchPrometheusServicesForSharedClusterApplications < ActiveRecord::Migrat
                    AND clusters_applications_prometheus.status IN (#{Applications::Prometheus.statuses[:installed]}, #{Applications::Prometheus.statuses[:updated]})").exists?
       end
     end
-
-    class PrometheusService < ActiveRecord::Base
-      self.inheritance_column = :_type_disabled
-      self.table_name = 'services'
-
-      default_scope { where("services.type = 'PrometheusService'") }
-
-      scope :managed, -> { where("services.properties = '{}'") }
-      scope :not_active, -> { where.not(active: true) }
-      scope :not_template, -> { where.not('services.template') }
-      scope :join_applications, -> {
-        joins('LEFT JOIN projects ON projects.id = services.project_id')
-          .joins('LEFT JOIN namespaces ON namespaces.id = projects.namespace_id')
-          .joins('LEFT JOIN cluster_groups ON cluster_groups.group_id = namespaces.id')
-          .joins("LEFT JOIN clusters ON clusters.cluster_type = #{Cluster.cluster_types['instance_type']} OR
-                            clusters.id = cluster_groups.cluster_id AND clusters.cluster_type = #{Cluster.cluster_types['group_type']}")
-          .joins('LEFT JOIN clusters_applications_prometheus ON clusters_applications_prometheus.cluster_id = clusters.id')
-      }
-    end
   end
 
   def up
@@ -84,16 +65,13 @@ class PatchPrometheusServicesForSharedClusterApplications < ActiveRecord::Migrat
   end
 
   def down
-    Migratable::PrometheusService.managed.not_template.not_active.delete_all
-    Migratable::PrometheusService.managed.not_template.where(project_id: services_without_active_application.select('project_id')).delete_all
-    clear_duplicates
+    # no-op
   end
 
   private
 
   def projects_without_active_prometheus_service
-    scope = Migratable::Project
-              .without_active_prometheus_services
+    scope = Migratable::Project.without_active_prometheus_services
 
     return scope if migrate_instance_cluster?
 
@@ -107,20 +85,4 @@ class PatchPrometheusServicesForSharedClusterApplications < ActiveRecord::Migrat
       @migrate_instance_cluster = Migratable::Cluster.instance_type.has_prometheus_application?
     end
   end
-
-  def services_without_active_application
-    Migratable::PrometheusService
-      .join_applications
-      .managed
-      .not_template
-      .group('project_id')
-      .having("NOT bool_or(COALESCE(clusters_applications_prometheus.status, #{Migratable::Applications::Prometheus.statuses[:errored]})
-                IN (#{Migratable::Applications::Prometheus.statuses[:installed]}, #{Migratable::Applications::Prometheus.statuses[:updated]}))")
-  end
-
-  def clear_duplicates
-    subquery = Migratable::PrometheusService.managed.not_template.select("id, ROW_NUMBER() OVER(PARTITION BY project_id ORDER BY project_id) AS row_num").to_sql
-    duplicates_filter = "id in (SELECT id FROM (#{subquery}) t WHERE t.row_num > 1)"
-    Migratable::PrometheusService.where(duplicates_filter).delete_all
-  end
 end

spec/migrations/patch_prometheus_services_for_shared_cluster_applications_spec.rb

@@ -131,42 +131,4 @@ describe PatchPrometheusServicesForSharedClusterApplications, :migration, :sidek
       it_behaves_like 'patch prometheus services post migration'
     end
   end
-
-  describe '#down' do
-    subject(:migration) { described_class.new }
-
-    let(:group) { namespaces.create!(name: 'group', path: 'gitlab-org') }
-    let(:project) { projects.create!(name: 'gitlab', path: 'gitlab-ee', namespace_id: namespace.id) }
-    let(:project_with_group_application) { projects.create!(name: 'gitlab', path: 'gitlab-ee', namespace_id: group.id) }
-    let!(:active_service_without_application_on_group_cluster) { services.create(service_params_for(project.id, active: true, title: 'to remove')) }
-    let!(:duplicated_active_service) { services.create(service_params_for(project_with_group_application.id, active: true)) }
-    let!(:inactive_service) { services.create(service_params_for(project_with_group_application.id, active: false)) }
-    let!(:manual_inactive_service) { services.create(service_params_for(project.id, active: false, properties: '{\'some\':\'param\'}')) }
-    let!(:active_service_group_application) { services.create(service_params_for(project_with_group_application.id, active: true)) }
-
-    before do
-      group_cluster = clusters.create(name: 'cluster', cluster_type: cluster_types[:group_type])
-      cluster_groups.create(group_id: group.id, cluster_id: group_cluster.id)
-      clusters_applications_prometheus.create(cluster_id: group_cluster.id, status: application_statuses[:installed], version: '123')
-    end
-
-    context 'application on group cluster' do
-      it 'removes only redundant and inconsistent entries' do
-        migration.down
-        expect(services.all.map(&method(:row_attributes))).to match_array([manual_inactive_service, active_service_group_application].map(&method(:row_attributes)))
-      end
-    end
-
-    context 'application on instance cluster' do
-      it 'removes only redundant and inconsistent entries' do
-        instance_cluster = clusters.create(name: 'cluster', cluster_type: cluster_types[:instance_type])
-        clusters_applications_prometheus.create(cluster_id: instance_cluster.id, status: application_statuses[:updated], version: '123')
-
-        migration.down
-
-        expected_rows = [active_service_without_application_on_group_cluster, manual_inactive_service, active_service_group_application].map(&method(:row_attributes))
-        expect(services.all.map(&method(:row_attributes))).to match_array(expected_rows)
-      end
-    end
-  end
 end