Hide license breakdown in /admin if user count is high

On GitLab.com, we observed statement timeouts counting the number of
active users minus guests:
https://gitlab.com/gitlab-org/gitlab/issues/32287.

To work around this problem, hide the license breakdown if the estimate
number of users exceeds 100,000.

app/controllers/admin/dashboard_controller.rb

@@ -2,6 +2,7 @@
 
 class Admin::DashboardController < Admin::ApplicationController
   include CountHelper
+  helper_method :show_license_breakdown?
 
   COUNTED_ITEMS = [Project, User, Group].freeze
 
@@ -13,6 +14,10 @@ class Admin::DashboardController < Admin::ApplicationController
     @groups = Group.order_id_desc.with_route.limit(10)
   end
   # rubocop: enable CodeReuse/ActiveRecord
+
+  def show_license_breakdown?
+    false
+  end
 end
 
 Admin::DashboardController.prepend_if_ee('EE::Admin::DashboardController')

app/views/admin/dashboard/index.html.haml

 - breadcrumb_title "Dashboard"
 
-= render_if_exists 'admin/licenses/breakdown', license: @license
+- if show_license_breakdown?
+  = render_if_exists 'admin/licenses/breakdown', license: @license
 
 .admin-dashboard.prepend-top-default
   .row

changelogs/unreleased/sh-hide-license-breakdown.yml

+---
+title: Hide license breakdown in /admin if user count is high
+merge_request: 18825
+author:
+type: performance

ee/app/controllers/ee/admin/dashboard_controller.rb

@@ -7,6 +7,8 @@ module EE
       extend ActiveSupport::Concern
       extend ::Gitlab::Utils::Override
 
+      LICENSE_BREAKDOWN_USER_LIMIT = 100_000
+
       override :index
       def index
         super
@@ -18,6 +20,16 @@ module EE
         @admin_count = ::User.admins.count
         @roles_count = ::ProjectAuthorization.roles_stats
       end
+
+      # The license section may time out if the number of users is
+      # high. To avoid 500 errors, just hide this section. This is a
+      # workaround for https://gitlab.com/gitlab-org/gitlab/issues/32287.
+      override :show_license_breakdown?
+      def show_license_breakdown?
+        return false unless @counts.is_a?(Hash)
+
+        @counts.fetch(::User, 0) < LICENSE_BREAKDOWN_USER_LIMIT
+      end
     end
   end
 end

ee/spec/controllers/admin/dashboard_controller_spec.rb

@@ -4,6 +4,8 @@ require 'spec_helper'
 
 describe Admin::DashboardController do
   describe '#index' do
+    render_views
+
     it "allows an admin user to access the page" do
       sign_in(create(:user, :admin))
 
@@ -27,5 +29,31 @@ describe Admin::DashboardController do
 
       expect(response).to have_gitlab_http_status(404)
     end
+
+    it 'shows the license breakdown' do
+      sign_in(create(:user, :admin))
+
+      get :index
+
+      expect(response.body).to include('Users in License')
+    end
+
+    context 'when the user count is high' do
+      let(:counts) do
+        described_class::COUNTED_ITEMS.each_with_object({}) { |model, hash| hash[model] = described_class::LICENSE_BREAKDOWN_USER_LIMIT + 1 }
+      end
+
+      before do
+        expect(Gitlab::Database::Count).to receive(:approximate_counts).and_return(counts)
+
+        sign_in(create(:admin))
+      end
+
+      it 'hides the license breakdown' do
+        get :index
+
+        expect(response.body).not_to include('Users in License')
+      end
+    end
   end
 end

spec/views/admin/dashboard/index.html.haml_spec.rb

@@ -17,6 +17,7 @@ describe 'admin/dashboard/index.html.haml' do
 
     allow(view).to receive(:admin?).and_return(true)
     allow(view).to receive(:current_application_settings).and_return(Gitlab::CurrentSettings.current_application_settings)
+    allow(view).to receive(:show_license_breakdown?).and_return(false)
   end
 
   it "shows version of GitLab Workhorse" do