Hi,
We've had a few performance issues caused by using the incorrect methods
for combining ActiveRecord relations. I happened to run across a good,
up-to-date article that explains the differences in a good concise manner,
sharing so you can all enjoy:
http://blog.scoutapp.com/articles/2017/01/24/activerecord-includes-vs-joins-vs-preload-vs-eager_load-when-and-where