How can I debug a "Application Error" in my heroku hosted Ruby on Rails web application?

I am getting a "Application Error" screen randomly during the day on my website that last up to 20 minutes.

When I use the basic logging module "heroku log开发者_StackOverflows", it doesn't show any error as if the "Application Error" never occurred.

When I use the new logging module on Heroku, same thing.

GetExceptional doesn't report anything.

How should I proceed to find what causes the error?

---

heroku config:set LOG_LEVEL=debug 

should help. if not, you can use the free addon "exceptiontrap"

---

You could install the exception notifier, which will send you an email for every 500 error including a full stack trace.

OT: The basic heroku logs (= free version) are pretty useless IMO.