Refactor BatchForksCountService class

In order to avoid multiple calls to Redis
we gather all the forks count in one mget
call.

Modify group detail class

Modify passed options

Fix rubocop offences

Fix specs

app/controllers/concerns/renders_member_access.rb

@@ -7,12 +7,6 @@ module RendersMemberAccess
     groups
   end
 
-  def prepare_projects_for_rendering(projects)
-    preload_max_member_access_for_collection(Project, projects)
-
-    projects
-  end
-
   private
 
   # rubocop: disable CodeReuse/ActiveRecord

app/controllers/concerns/renders_projects_list.rb

+# frozen_string_literal: true
+
+module RendersProjectsList
+  def prepare_projects_for_rendering(projects)
+    preload_max_member_access_for_collection(Project, projects)
+
+    # Call the forks count method on every project, so the BatchLoader would load them all at
+    # once when the entities are rendered
+    projects.each(&:forks_count)
+
+    projects
+  end
+end

app/controllers/dashboard/projects_controller.rb

@@ -3,6 +3,7 @@
 class Dashboard::ProjectsController < Dashboard::ApplicationController
   include ParamsBackwardCompatibility
   include RendersMemberAccess
+  include RendersProjectsList
   include SortingHelper
   include SortingPreference
   include FiltersEvents

app/controllers/explore/projects_controller.rb

@@ -4,6 +4,7 @@ class Explore::ProjectsController < Explore::ApplicationController
   include PageLimiter
   include ParamsBackwardCompatibility
   include RendersMemberAccess
+  include RendersProjectsList
   include SortingHelper
   include SortingPreference
 

app/controllers/projects/forks_controller.rb

@@ -3,6 +3,7 @@
 class Projects::ForksController < Projects::ApplicationController
   include ContinueParams
   include RendersMemberAccess
+  include RendersProjectsList
   include Gitlab::Utils::StrongMemoize
 
   # Authorize

app/controllers/root_controller.rb

@@ -13,10 +13,15 @@ class RootController < Dashboard::ProjectsController
 
   before_action :redirect_unlogged_user, if: -> { current_user.nil? }
   before_action :redirect_logged_user, if: -> { current_user.present? }
+  # We only need to load the projects when the user is logged in but did not
+  # configure a dashboard. In which case we render projects. We can do that straight
+  # from the #index action.
+  skip_before_action :projects
 
   def index
     # n+1: https://gitlab.com/gitlab-org/gitlab-foss/issues/40260
     Gitlab::GitalyClient.allow_n_plus_1_calls do
+      projects
       super
     end
   end

app/controllers/users_controller.rb

@@ -3,6 +3,7 @@
 class UsersController < ApplicationController
   include RoutableActions
   include RendersMemberAccess
+  include RendersProjectsList
   include ControllerWithCrossProjectAccessCheck
   include Gitlab::NoteableMetadata
 

app/models/project.rb

@@ -2153,7 +2153,13 @@ class Project < ApplicationRecord
 
   # rubocop: disable CodeReuse/ServiceClass
   def forks_count
-    Projects::ForksCountService.new(self).count
+    BatchLoader.for(self).batch do |projects, loader|
+      fork_count_per_project = ::Projects::BatchForksCountService.new(projects).refresh_cache_and_retrieve_data
+
+      fork_count_per_project.each do |project, count|
+        loader.call(project, count)
+      end
+    end
   end
   # rubocop: enable CodeReuse/ServiceClass
 

app/services/projects/batch_forks_count_service.rb

@@ -5,6 +5,21 @@
 # because the service use maps to retrieve the project ids
 module Projects
   class BatchForksCountService < Projects::BatchCountService
+    def refresh_cache_and_retrieve_data
+      count_services = @projects.map { |project| count_service.new(project) }
+
+      values = Gitlab::Instrumentation::RedisClusterValidator.allow_cross_slot_commands do
+        Rails.cache.fetch_multi(*(count_services.map { |ser| ser.cache_key } )) { |key| nil }
+      end
+
+      results_per_service = Hash[count_services.zip(values.values)]
+      projects_to_refresh = results_per_service.select { |_k, value| value.nil? }
+      projects_to_refresh = recreate_cache(projects_to_refresh)
+
+      results_per_service.update(projects_to_refresh)
+      results_per_service.transform_keys { |k| k.project }
+    end
+
     # rubocop: disable CodeReuse/ActiveRecord
     def global_count
       @global_count ||= begin
@@ -18,5 +33,13 @@ module Projects
     def count_service
       ::Projects::ForksCountService
     end
+
+    def recreate_cache(projects_to_refresh)
+      projects_to_refresh.each_with_object({}) do |(service, _v), hash|
+        count = global_count[service.project.id].to_i
+        service.refresh_cache { count }
+        hash[service] = count
+      end
+    end
   end
 end

app/services/projects/forks_count_service.rb

@@ -3,6 +3,8 @@
 module Projects
   # Service class for getting and caching the number of forks of a project.
   class ForksCountService < Projects::CountService
+    attr_reader :project
+
     def cache_key_name
       'forks_count'
     end

changelogs/unreleased/220316-redis-n-1-in-api-v4-groups-id-projects-forks-count-key.yml

+---
+title: Use BatchLoader for Project.forks_count to limit calls to Redis
+merge_request: 35328
+author:
+type: performance

lib/api/entities/basic_project_details.rb

@@ -33,7 +33,8 @@ module API
         project.avatar_url(only_path: false)
       end
 
-      expose :star_count, :forks_count
+      expose :forks_count
+      expose :star_count
       expose :last_activity_at
       expose :namespace, using: 'API::Entities::NamespaceBasic'
       expose :custom_attributes, using: 'API::Entities::CustomAttribute', if: :with_custom_attributes

lib/api/entities/group_detail.rb

@@ -7,6 +7,7 @@ module API
         SharedGroupWithGroup.represent(group.shared_with_group_links.public_or_visible_to_user(group, options[:current_user]))
       end
       expose :runners_token, if: lambda { |group, options| options[:user_can_admin_group] }
+
       expose :projects, using: Entities::Project do |group, options|
         projects = GroupProjectsFinder.new(
           group: group,

lib/api/projects_relation_builder.rb

@@ -8,6 +8,10 @@ module API
       def prepare_relation(projects_relation, options = {})
         projects_relation = preload_relation(projects_relation, options)
         execute_batch_counting(projects_relation)
+        # Call the forks count method on every project, so the BatchLoader would load them all at
+        # once when the entities are rendered
+        projects_relation.each(&:forks_count)
+
         projects_relation
       end
 
@@ -19,16 +23,11 @@ module API
         projects_relation
       end
 
-      def batch_forks_counting(projects_relation)
-        ::Projects::BatchForksCountService.new(forks_counting_projects(projects_relation)).refresh_cache
-      end
-
       def batch_open_issues_counting(projects_relation)
         ::Projects::BatchOpenIssuesCountService.new(projects_relation).refresh_cache
       end
 
       def execute_batch_counting(projects_relation)
-        batch_forks_counting(projects_relation)
         batch_open_issues_counting(projects_relation)
       end
     end

spec/models/project_spec.rb

@@ -4116,7 +4116,7 @@ RSpec.describe Project do
     it 'returns the number of forks' do
       project = build(:project)
 
-      expect_any_instance_of(Projects::ForksCountService).to receive(:count).and_return(1)
+      expect_any_instance_of(::Projects::BatchForksCountService).to receive(:refresh_cache_and_retrieve_data).and_return({ project => 1 })
 
       expect(project.forks_count).to eq(1)
     end

spec/services/projects/fork_service_spec.rb

@@ -10,6 +10,7 @@ RSpec.describe Projects::ForkService do
       expect(from_project.forks_count).to be_zero
 
       fork_project(from_project, to_user)
+      BatchLoader::Executor.clear_current
 
       expect(from_project.forks_count).to eq(1)
     end
@@ -405,6 +406,7 @@ RSpec.describe Projects::ForkService do
         expect(fork_from_project.forks_count).to be_zero
 
         subject.execute(fork_to_project)
+        BatchLoader::Executor.clear_current
 
         expect(fork_from_project.forks_count).to eq(1)
       end

spec/services/projects/unlink_fork_service_spec.rb

@@ -53,6 +53,7 @@ RSpec.describe Projects::UnlinkForkService, :use_clean_rails_memory_store_cachin
     expect(source.forks_count).to eq(1)
 
     subject.execute
+    BatchLoader::Executor.clear_current
 
     expect(source.forks_count).to be_zero
   end
@@ -146,6 +147,7 @@ RSpec.describe Projects::UnlinkForkService, :use_clean_rails_memory_store_cachin
       expect(project.forks_count).to eq(2)
 
       subject.execute
+      BatchLoader::Executor.clear_current
 
       expect(project.forks_count).to be_zero
     end
@@ -212,6 +214,7 @@ RSpec.describe Projects::UnlinkForkService, :use_clean_rails_memory_store_cachin
         expect(forked_project.forks_count).to eq(1)
 
         subject.execute
+        BatchLoader::Executor.clear_current
 
         expect(project.forks_count).to eq(1)
         expect(forked_project.forks_count).to eq(0)