Message from 2021
This post is pretty old! Opinions and technical information in it are almost certainly oudated. Commands and configurations will probably not work. Consider the age of the content before putting any of it into practice.
For those situations where you want multiple threads doing database stuff in your Ruby app (but not in Rails - threading Rails doesn’t make much sense), turn ActiveRecord’s concurrency support on:
ActiveRecord::Base.allow_concurrency = true
Found on this useful blog.