Create namespace descendants table

This change adds a cache table for storing namespace descendants and
project ids so we can retrieve them efficiently.

Changelog: added

app/models/namespaces/descendants.rb

+# frozen_string_literal: true
+
+module Namespaces
+  class Descendants < ApplicationRecord
+    self.table_name = :namespace_descendants
+
+    belongs_to :namespace
+
+    validates :namespace_id, uniqueness: true
+  end
+end

db/docs/namespace_descendants.yml

+---
+table_name: namespace_descendants
+classes:
+- Namespaces::Descendants
+feature_categories:
+- groups_and_projects
+description: Storing de-normalized descendant ids for Namespace records
+introduced_by_url:
+milestone: '16.8'
+gitlab_schema: gitlab_main_cell
+sharding_key:
+  namespace_id: namespaces

db/migrate/20231221171135_create_namespace_descendants_table.rb

+# frozen_string_literal: true
+
+class CreateNamespaceDescendantsTable < Gitlab::Database::Migration[2.2]
+  include Gitlab::Database::PartitioningMigrationHelpers::TableManagementHelpers
+
+  milestone '16.8'
+
+  def up
+    execute <<~SQL
+      CREATE TABLE namespace_descendants (
+        namespace_id bigint NOT NULL,
+        self_and_descendant_group_ids bigint[] NOT NULL DEFAULT ARRAY[]::bigint[],
+        all_project_ids bigint[] NOT NULL DEFAULT ARRAY[]::bigint[],
+        traversal_ids bigint[] NOT NULL DEFAULT ARRAY[]::bigint[],
+        outdated_at timestamp with time zone,
+        calculated_at timestamp with time zone,
+        PRIMARY KEY(namespace_id)
+      )
+      PARTITION BY HASH (namespace_id);
+    SQL
+
+    execute <<~SQL
+      CREATE INDEX
+      index_on_namespace_descendants_outdated
+      ON namespace_descendants (namespace_id)
+      WHERE outdated_at IS NOT NULL
+    SQL
+
+    create_hash_partitions(:namespace_descendants, 32)
+  end
+
+  def down
+    drop_table :namespace_descendants
+  end
+end

db/schema_migrations/20231221171135

+b03eee7eff8f7402f3c590b6ae2010c6c278aaa433db52d444a60357bbd8b582
\ No newline at end of file

spec/db/schema_spec.rb

@@ -87,6 +87,7 @@
     merge_request_diffs: %w[project_id],
     merge_request_diff_commits: %w[commit_author_id committer_id],
     namespaces: %w[owner_id parent_id],
+    namespace_descendants: %w[namespace_id],
     notes: %w[author_id commit_id noteable_id updated_by_id resolved_by_id confirmed_by_id discussion_id namespace_id],
     notification_settings: %w[source_id],
     oauth_access_grants: %w[resource_owner_id application_id],

spec/factories/namespaces/descendants.rb

+# frozen_string_literal: true
+
+FactoryBot.define do
+  factory :namespace_descendants, class: 'Namespaces::Descendants' do
+    namespace { association(:group) }
+    self_and_descendant_group_ids { namespace.self_and_descendant_ids.pluck(:id).sort }
+    all_project_ids { namespace.all_projects.pluck(:id).sort }
+    traversal_ids { namespace.traversal_ids }
+    outdated_at { nil }
+    calculated_at { Time.current }
+  end
+end

spec/lib/gitlab/database/sharding_key_spec.rb

@@ -27,7 +27,8 @@
   let(:allowed_to_be_missing_foreign_key) do
     [
       'p_catalog_resource_sync_events.project_id',
-      'zoekt_indices.namespace_id'
+      'zoekt_indices.namespace_id',
+      'namespace_descendants.namespace_id'
     ]
   end
 

spec/models/namespaces/descendants_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Namespaces::Descendants, feature_category: :database do
+  describe 'associations' do
+    it { is_expected.to belong_to(:namespace) }
+  end
+
+  describe 'validations' do
+    subject(:namespace_descendants) { create(:namespace_descendants) }
+
+    it { is_expected.to validate_uniqueness_of(:namespace_id) }
+  end
+
+  describe 'factory' do
+    let_it_be(:group) { create(:group) }
+    let_it_be(:subgroup) { create(:group, parent: group) }
+
+    let_it_be(:project1) { create(:project, group: subgroup) }
+    let_it_be(:project2) { create(:project, group: group) }
+
+    it 'up to date descendant record for a group' do
+      descendants = create(:namespace_descendants, namespace: group)
+
+      expect(descendants).to have_attributes(
+        self_and_descendant_group_ids: [group.id, subgroup.id],
+        all_project_ids: [project1.id, project2.id],
+        traversal_ids: [group.id]
+      )
+    end
+
+    it 'creates up-to-date descendant record for a subgroup' do
+      descendants = create(:namespace_descendants, namespace: subgroup)
+
+      expect(descendants).to have_attributes(
+        self_and_descendant_group_ids: [subgroup.id],
+        all_project_ids: [project1.id],
+        traversal_ids: [group.id, subgroup.id]
+      )
+    end
+  end
+end