Merge branch '47496-more-n-1s-in-calculating-notification-recipients' into 'master'

Resolve "More N+1s in calculating notification recipients"

Closes #47496

See merge request gitlab-org/gitlab-ce!22050

app/models/concerns/subscribable.rb

@@ -31,9 +31,11 @@ module Subscribable
   end
 
   def subscribers(project)
-    subscriptions_available(project)
+    relation = subscriptions_available(project)
                  .where(subscribed: true)
-      .map(&:user)
+                 .select(:user_id)
+
+    User.where(id: relation)
   end
 
   def toggle_subscription(user, project = nil)

app/policies/project_policy.rb

@@ -390,7 +390,11 @@ class ProjectPolicy < BasePolicy
     greedy_load_subject ||= !@user.persisted?
 
     if greedy_load_subject
-      project.team.members.include?(user)
+      # We want to load all the members with one query. Calling #include? on
+      # project.team.members will perform a separate query for each user, unless
+      # project.team.members was loaded before somewhere else. Calling #to_a
+      # ensures it's always loaded before checking for membership.
+      project.team.members.to_a.include?(user)
     else
       # otherwise we just make a specific query for
       # this particular user.

changelogs/unreleased/47496-more-n-1s-in-calculating-notification-recipients.yml

+---
+title: Reduce queries needed to compute notification recipients
+merge_request: 22050
+author:
+type: performance

spec/services/notification_recipient_service_spec.rb

@@ -10,7 +10,24 @@ describe NotificationRecipientService do
     let(:issue) { create(:issue, project: project, assignees: [assignee]) }
     let(:note) { create(:note_on_issue, noteable: issue, project_id: issue.project_id) }
 
-    def create_watcher
+    shared_examples 'no N+1 queries' do
+      it 'avoids N+1 queries', :request_store do
+        create_user
+
+        service.build_new_note_recipients(note)
+
+        control_count = ActiveRecord::QueryRecorder.new do
+          service.build_new_note_recipients(note)
+        end
+
+        create_user
+
+        expect { service.build_new_note_recipients(note) }.not_to exceed_query_limit(control_count)
+      end
+    end
+
+    context 'when there are multiple watchers' do
+      def create_user
         watcher = create(:user)
         create(:notification_setting, source: project, user: watcher, level: :watch)
 
@@ -19,18 +36,24 @@ describe NotificationRecipientService do
         end
       end
 
-    it 'avoids N+1 queries', :request_store do
-      create_watcher
-
-      service.build_new_note_recipients(note)
+      include_examples 'no N+1 queries'
+    end
 
-      control_count = ActiveRecord::QueryRecorder.new do
-        service.build_new_note_recipients(note)
+    context 'when there are multiple subscribers' do
+      def create_user
+        subscriber = create(:user)
+        issue.subscriptions.create(user: subscriber, project: project, subscribed: true)
       end
 
-      create_watcher
+      include_examples 'no N+1 queries'
 
-      expect { service.build_new_note_recipients(note) }.not_to exceed_query_limit(control_count)
+      context 'when the project is private' do
+        before do
+          project.update!(visibility_level: Gitlab::VisibilityLevel::PRIVATE)
+        end
+
+        include_examples 'no N+1 queries'
+      end
     end
   end
 end