When storing large JSON files, how efficiently does ActiveRecord's jsonb field store and retrieve large JSON files when compared to a json field, or a regular String field?

In describing their process upgrading from Rails 3.2 to Rails 4.2 at February's Ruby Lightning Talks T.O., Canadian startup 500px experienced significant drops in performance in some areas. They shared one example of code that was outright baffling. This article is an explanation of my investigation into this problem.

In adding the ability in my application for registered users to invite new, unregistered users I created a few polymorphic relationships. This tutorial walks through adjusting the Item model to be polymorphic, and highlights a few interesting consequences of doing so.