Cache assigned merge request count. Closes #18036

app/models/user.rb

@@ -776,6 +776,12 @@ class User < ActiveRecord::Base
     notification_settings.find_or_initialize_by(source: source)
   end
 
+  def assigned_open_merge_request_count
+    Rails.cache.fetch(['users', id, 'assigned_open_merge_request_count'], expires_in: 60) do
+       assigned_merge_requests.opened.count
+     end
+  end
+
   private
 
   def projects_union

app/views/layouts/nav/_dashboard.html.haml

@@ -36,7 +36,7 @@
       = icon('tasks fw')
       %span
         Merge Requests
-        %span.count= number_with_delimiter(current_user.assigned_merge_requests.opened.count)
+        %span.count= number_with_delimiter(current_user.assigned_open_merge_request_count)
   = nav_link(controller: :snippets) do
     = link_to dashboard_snippets_path, title: 'Snippets' do
       = icon('clipboard fw')