After the migration of our Moodle from 3.11 to 4.1.3, I realised that the average response time of a Forum or Assign page (view.php) is slower about 1s :

• In 3.11
  • Forum view : ~1.9s
  • Assign view : ~1.8s
• In 4.1.3
  • Forum view : ~2.9s
  • Assign view : ~2.8s
    Here is our dataset :
• Number of users : ~370k
• Number of course categories : 201
• Number of courses : 125428
• Number of forum : 202410
• Number of forum discussions : 1037404
  The performace test is simple, I use XHProf and configure to profile 2 pages /mod/forum/view.php and /mod/assign/view.php on our current dataset

By inspecting the profiling of these pages, I found that the time to render the UI in 4.1.3 is much slower than 3.11, for example the second navigation which is new in 4.x version takes about 0.5s.