Introduce project_settings table

There is no usable data in this table yet, but with this change the
table is created, it's backfilled for every existing project, and new
rows are created as new projects are created. When the background
migration is complete it should be fairly easy to add columns to this
table and store project settings data in this table instead of in the
projects table itself.

This is a first step toward:
https://gitlab.com/gitlab-org/gitlab/issues/19826

app/models/project.rb

@@ -190,6 +190,7 @@ class Project < ApplicationRecord
   has_one :error_tracking_setting, inverse_of: :project, class_name: 'ErrorTracking::ProjectErrorTrackingSetting'
   has_one :metrics_setting, inverse_of: :project, class_name: 'ProjectMetricsSetting'
   has_one :grafana_integration, inverse_of: :project
+  has_one :settings, inverse_of: :project, class_name: 'ProjectSettings'
 
   # Merge Requests for target project should be removed with it
   has_many :merge_requests, foreign_key: 'target_project_id', inverse_of: :target_project

app/models/project_settings.rb

+# frozen_string_literal: true
+
+class ProjectSettings < ApplicationRecord
+  belongs_to :project, inverse_of: :settings
+
+  self.primary_key = :project_id
+end

app/services/projects/create_service.rb

@@ -90,6 +90,7 @@ module Projects
       end
 
       @project.track_project_repository
+      @project.create_settings
 
       event_service.create_project(@project, current_user)
       system_hook_service.execute_hooks_for(@project, :create)

changelogs/unreleased/tc-create-project-settings.yml

+---
+title: Introduce project_settings table
+merge_request: 19761
+author:
+type: added

db/migrate/20191031095636_create_project_settings.rb

+# frozen_string_literal: true
+
+class CreateProjectSettings < ActiveRecord::Migration[5.2]
+  DOWNTIME = false
+
+  def change
+    create_table :project_settings, id: false do |t|
+      t.timestamps_with_timezone null: false
+      t.references :project, primary_key: true, default: nil, type: :integer, index: false, foreign_key: { on_delete: :cascade }
+    end
+  end
+end

db/post_migrate/20200122123016_backfill_project_settings.rb

+# frozen_string_literal: true
+
+class BackfillProjectSettings < ActiveRecord::Migration[5.2]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  MIGRATION = 'BackfillProjectSettings'
+  DELAY_INTERVAL = 2.minutes
+  BATCH_SIZE = 10_000
+
+  disable_ddl_transaction!
+
+  class Project < ActiveRecord::Base
+    include EachBatch
+
+    self.table_name = 'projects'
+  end
+
+  def up
+    say "Scheduling `#{MIGRATION}` jobs"
+
+    queue_background_migration_jobs_by_range_at_intervals(Project, MIGRATION, DELAY_INTERVAL, batch_size: BATCH_SIZE)
+  end
+
+  def down
+    # NOOP
+  end
+end

db/schema.rb

@@ -3296,6 +3296,11 @@ ActiveRecord::Schema.define(version: 2020_02_06_111847) do
     t.index ["project_id"], name: "index_project_repository_states_on_project_id", unique: true
   end
 
+  create_table "project_settings", primary_key: "project_id", id: :integer, default: nil, force: :cascade do |t|
+    t.datetime_with_timezone "created_at", null: false
+    t.datetime_with_timezone "updated_at", null: false
+  end
+
   create_table "project_statistics", id: :serial, force: :cascade do |t|
     t.integer "project_id", null: false
     t.integer "namespace_id", null: false
@@ -4881,6 +4886,7 @@ ActiveRecord::Schema.define(version: 2020_02_06_111847) do
   add_foreign_key "project_repositories", "projects", on_delete: :cascade
   add_foreign_key "project_repositories", "shards", on_delete: :restrict
   add_foreign_key "project_repository_states", "projects", on_delete: :cascade
+  add_foreign_key "project_settings", "projects", on_delete: :cascade
   add_foreign_key "project_statistics", "projects", on_delete: :cascade
   add_foreign_key "project_tracing_settings", "projects", on_delete: :cascade
   add_foreign_key "projects", "pool_repositories", name: "fk_6e5c14658a", on_delete: :nullify

lib/gitlab/background_migration/backfill_project_settings.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module BackgroundMigration
+    # Backfill project_settings for a range of projects
+    class BackfillProjectSettings
+      def perform(start_id, end_id)
+        ActiveRecord::Base.connection.execute <<~SQL
+          INSERT INTO project_settings (project_id, created_at, updated_at)
+            SELECT projects.id, now(), now()
+            FROM projects
+            WHERE projects.id BETWEEN #{start_id} AND #{end_id}
+          ON CONFLICT (project_id) DO NOTHING;
+        SQL
+      end
+    end
+  end
+end

spec/lib/gitlab/background_migration/backfill_project_settings_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::BackgroundMigration::BackfillProjectSettings, :migration, schema: 20200114113341 do
+  let(:projects) { table(:projects) }
+  let(:project_settings) { table(:project_settings) }
+  let(:namespace) { table(:namespaces).create(name: 'user', path: 'user') }
+  let(:project) { projects.create(namespace_id: namespace.id) }
+
+  subject { described_class.new }
+
+  describe '#perform' do
+    it 'creates settings for all projects in range' do
+      projects.create(id: 5, namespace_id: namespace.id)
+      projects.create(id: 7, namespace_id: namespace.id)
+      projects.create(id: 8, namespace_id: namespace.id)
+
+      subject.perform(5, 7)
+
+      expect(project_settings.all.pluck(:project_id)).to contain_exactly(5, 7)
+    end
+  end
+end

spec/migrations/20200122123016_backfill_project_settings_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+require Rails.root.join('db', 'post_migrate', '20200122123016_backfill_project_settings.rb')
+
+describe BackfillProjectSettings, :migration, :sidekiq, schema: 20200114113341 do
+  let(:projects) { table(:projects) }
+  let(:namespace) { table(:namespaces).create(name: 'user', path: 'user') }
+  let(:project) { projects.create(namespace_id: namespace.id) }
+
+  describe '#up' do
+    before do
+      stub_const("#{described_class}::BATCH_SIZE", 2)
+
+      projects.create(id: 1, namespace_id: namespace.id)
+      projects.create(id: 2, namespace_id: namespace.id)
+      projects.create(id: 3, namespace_id: namespace.id)
+    end
+
+    it 'schedules BackfillProjectSettings background jobs' do
+      Sidekiq::Testing.fake! do
+        Timecop.freeze do
+          migrate!
+
+          expect(described_class::MIGRATION).to be_scheduled_delayed_migration(2.minutes, 1, 2)
+          expect(described_class::MIGRATION).to be_scheduled_delayed_migration(4.minutes, 3, 3)
+          expect(BackgroundMigrationWorker.jobs.size).to eq(2)
+        end
+      end
+    end
+  end
+end

spec/models/project_settings_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe ProjectSettings, type: :model do
+  it { is_expected.to belong_to(:project) }
+end

spec/models/project_spec.rb

@@ -69,6 +69,7 @@ describe Project do
     it { is_expected.to have_one(:forked_from_project).through(:fork_network_member) }
     it { is_expected.to have_one(:auto_devops).class_name('ProjectAutoDevops') }
     it { is_expected.to have_one(:error_tracking_setting).class_name('ErrorTracking::ProjectErrorTrackingSetting') }
+    it { is_expected.to have_one(:settings).class_name('ProjectSettings') }
     it { is_expected.to have_many(:commit_statuses) }
     it { is_expected.to have_many(:ci_pipelines) }
     it { is_expected.to have_many(:builds) }

spec/services/projects/create_service_spec.rb

@@ -43,6 +43,12 @@ describe Projects::CreateService, '#execute' do
 
       create_project(user, opts)
     end
+
+    it 'creates associated project settings' do
+      project = create_project(user, opts)
+
+      expect(project.settings).to be_persisted
+    end
   end
 
   context "admin creates project with other user's namespace_id" do