Remove temporary index at services on project_id

changelogs/unreleased/196858-cleanup-temporary-index-at-services-table-on-project_id.yml

+---
+title: Remove temporary index at services on project_id
+merge_request: 24263
+author:
+type: removed

db/post_migrate/20200203104214_services_remove_temporary_index_on_project_id.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 ServicesRemoveTemporaryIndexOnProjectId < ActiveRecord::Migration[6.0]
+  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
+    remove_concurrent_index :services, :project_id, where: PARTIAL_FILTER, name: INDEX_NAME
+  end
+
+  def down
+    add_concurrent_index :services, :project_id, where: PARTIAL_FILTER, name: INDEX_NAME
+  end
+end

db/schema.rb

@@ -3846,7 +3846,6 @@ ActiveRecord::Schema.define(version: 2020_02_06_111847) do
     t.boolean "instance", default: false
     t.index ["instance"], name: "index_services_on_instance"
     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 ["type"], name: "index_services_on_type"
   end
 

spec/migrations/services_remove_temporary_index_on_project_id_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require Rails.root.join('db', 'post_migrate', '20200203104214_services_remove_temporary_index_on_project_id.rb')
+
+describe ServicesRemoveTemporaryIndexOnProjectId, :migration do
+  let(:migration_instance) { described_class.new }
+
+  it 'adds and removes temporary partial index in up and down methods' do
+    reversible_migration do |migration|
+      migration.before -> {
+        expect(migration_instance.index_exists?(:services, :project_id, name: described_class::INDEX_NAME)).to be true
+      }
+
+      migration.after -> {
+        expect(migration_instance.index_exists?(:services, :project_id, name: described_class::INDEX_NAME)).to be false
+      }
+    end
+  end
+
+  describe '#up' do
+    context 'index does not exist' do
+      it 'skips removal action' do
+        migrate!
+
+        expect { migrate! }.not_to change { migration_instance.index_exists?(:services, :project_id, name: described_class::INDEX_NAME) }
+      end
+    end
+  end
+
+  describe '#down' do
+    context 'index already exists' do
+      it 'skips creation of duplicated temporary partial index on project_id' do
+        schema_migrate_down!
+
+        expect { schema_migrate_down! }.not_to change { migration_instance.index_exists?(:services, :project_id, name: described_class::INDEX_NAME) }
+      end
+    end
+  end
+end