Add partial index on services

To make patch_prometheus_services_for_shared_cluster_applications.rb
more performant we need to add temproary index to serivces table.

db/post_migrate/20200114112932_add_temporary_partial_index_on_project_id_to_services.rb

+# frozen_string_literal: true
+
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddTemporaryPartialIndexOnProjectIdToServices < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  INDEX_NAME = 'tmp_index_on_project_id_partial_with_prometheus_services'
+  PARTIAL_FILTER = "type = 'PrometheusService'"
+
+  disable_ddl_transaction!
+
+  def up
+    add_concurrent_index :services, :project_id, where: PARTIAL_FILTER, name: INDEX_NAME
+  end
+
+  def down
+    remove_concurrent_index :services, :project_id, where: PARTIAL_FILTER, name: INDEX_NAME
+  end
+end

db/post_migrate/20200114113341_patch_prometheus_services_for_shared_cluster_applications.rb

+# frozen_string_literal: true
+
+class PatchPrometheusServicesForSharedClusterApplications < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  MIGRATION = 'ActivatePrometheusServicesForSharedClusterApplications'.freeze
+  BATCH_SIZE = 500
+  DELAY = 2.minutes
+
+  disable_ddl_transaction!
+
+  module Migratable
+    module Applications
+      class Prometheus < ActiveRecord::Base
+        self.table_name = 'clusters_applications_prometheus'
+
+        enum status: {
+          errored: -1,
+          installed: 3,
+          updated: 5
+        }
+      end
+    end
+
+    class Project < ActiveRecord::Base
+      self.table_name = 'projects'
+      include ::EachBatch
+
+      scope :with_application_on_group_clusters, -> {
+        joins("INNER JOIN namespaces ON namespaces.id = projects.namespace_id")
+          .joins("INNER JOIN cluster_groups ON cluster_groups.group_id = namespaces.id")
+          .joins("INNER JOIN clusters ON clusters.id = cluster_groups.cluster_id AND clusters.cluster_type = #{Cluster.cluster_types['group_type']}")
+          .joins("INNER JOIN clusters_applications_prometheus ON clusters_applications_prometheus.cluster_id = clusters.id
+                      AND clusters_applications_prometheus.status IN (#{Applications::Prometheus.statuses[:installed]}, #{Applications::Prometheus.statuses[:updated]})")
+      }
+
+      scope :without_active_prometheus_services, -> {
+        joins("LEFT JOIN services ON services.project_id = projects.id AND services.type = 'PrometheusService'")
+          .where("services.id IS NULL OR (services.active = FALSE AND services.properties = '{}')")
+      }
+    end
+
+    class Cluster < ActiveRecord::Base
+      self.table_name = 'clusters'
+
+      enum cluster_type: {
+        instance_type: 1,
+        group_type: 2
+      }
+
+      def self.has_prometheus_application?
+        joins("INNER JOIN clusters_applications_prometheus ON clusters_applications_prometheus.cluster_id = clusters.id
+                   AND clusters_applications_prometheus.status IN (#{Applications::Prometheus.statuses[:installed]}, #{Applications::Prometheus.statuses[:updated]})").exists?
+      end
+    end
+  end
+
+  def up
+    projects_without_active_prometheus_service.group('projects.id').each_batch(of: BATCH_SIZE) do |batch, index|
+      bg_migrations_batch = batch.select('projects.id').map { |project| [MIGRATION, project.id] }
+      delay = index * DELAY
+      BackgroundMigrationWorker.bulk_perform_in(delay.seconds, bg_migrations_batch)
+    end
+  end
+
+  def down
+    # no-op
+  end
+
+  private
+
+  def projects_without_active_prometheus_service
+    scope = Migratable::Project.without_active_prometheus_services
+
+    return scope if migrate_instance_cluster?
+
+    scope.with_application_on_group_clusters
+  end
+
+  def migrate_instance_cluster?
+    if instance_variable_defined?('@migrate_instance_cluster')
+      @migrate_instance_cluster
+    else
+      @migrate_instance_cluster = Migratable::Cluster.instance_type.has_prometheus_application?
+    end
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2020_01_13_133352) do
+ActiveRecord::Schema.define(version: 2020_01_14_112932) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "pg_trgm"
@@ -3769,6 +3769,7 @@ ActiveRecord::Schema.define(version: 2020_01_13_133352) do
     t.string "description", limit: 500
     t.boolean "comment_on_event_enabled", default: true, null: false
     t.index ["project_id"], name: "index_services_on_project_id"
+    t.index ["project_id"], name: "tmp_index_on_project_id_partial_with_prometheus_services", where: "((type)::text = 'PrometheusService'::text)"
     t.index ["template"], name: "index_services_on_template"
     t.index ["type"], name: "index_services_on_type"
   end

spec/migrations/add_temporary_partial_index_on_project_id_to_services_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require Rails.root.join('db', 'post_migrate', '20200114112932_add_temporary_partial_index_on_project_id_to_services.rb')
+
+describe AddTemporaryPartialIndexOnProjectIdToServices, :migration do
+  let(:migration) { described_class.new }
+
+  describe '#up' do
+    it 'creates temporary partial index on type' do
+      expect { migration.up }.to change { migration.index_exists?(:services, :project_id, name: described_class::INDEX_NAME) }.from(false).to(true)
+    end
+  end
+
+  describe '#down' do
+    it 'removes temporary partial index on type' do
+      migration.up
+
+      expect { migration.down }.to change { migration.index_exists?(:services, :project_id, name: described_class::INDEX_NAME) }.from(true).to(false)
+    end
+  end
+end