Notifier issues

We sometimes have issues with notifier.

notifier-celery-workers FATAL Exited too quickly (process log may have details)

From the logs, we can clearly see that it is because:
OperationalError: database is locked

It there a good solution to this issue apart from moving notifier from sqlite to mysql? Is there a reason why notifier runs by default on sqlite?

I’ve seen lots of potential solutions on the web, but no process or user is locking down the database as far as I can see. Restarting notifier-celery-workers doesn’t help either. Any suggestions? Thanks in advance.

Inquiring minds want to know…