NewNoteWorker#perform became slow

The new_note Sidekiq worker got really slow today (https://performance.gitlab.net/dashboard/db/sidekiq-workers?orgId=1&var-worker=NewNoteWorker%23perform&var-database=Production&from=now-24h&to=now), and this is leading to a build-up of the Sidekiq queues:

The SQL timings seems suspect:

A TTIN signal to a sidekiq-cluster on realtime-03 worker with two new_note workers shows the SQL busy on two places:

1. User#find_by_any_email
2. User#notification_settings_for

newnote.txt