We have a relatively standard Ruby on Rails project, which has quite a few background jobs that run under Resque (with Redis as a backend.)
The issue is that very rarely -- perhaps once a month, maybe a little less -- we'll suddenly see floods of exceptions from Resque. The exceptions are all in the following vein:
undefined method `find_by_id` for User():Class
undefined method `find_by_name` for CustomerAccount():Class
undefined method `find_by_id` for Job():Class
It appears that suddenly, all ActiveRecord::Base models lose their find_by_* methods for the entire thread. Restarting the worker fixes the issue.
I know that generically, the answer must be "someone, somewhere -- probably in a gem -- is breaking method_missing somehow." Or perhaps, somehow the constants are getting reassigned to a different class. But before I begin a really thorough investigation, I wanted to check if anyone has run into this problem and solved it already.
This project is running Ruby 2.1.1p76, Rails 3.2.17, Resque 1.25.1.
Closing the loop on this ancient question: it turns out moonfly's comment was indeed the issue, and in long-running workers, a dropped database connection would result in this (somewhat strange) error message.
Knowing the root cause, we were able to add a periodic conn refresh (to try and keep the connection alive when a worker was idle for too long), and also, to add a detection mechanism for when a db conn was dropped, and to reconnect. So, thanks much @moonfly, if you'd like to turn your comment into an answer I'm happy to award you much-delayed answer credit.