Controlling Drupal 9 Caching

Drupal 8 and later has a much more sophisticated and ultimately aggressive caching system.  While this is supposed to be a good change, sometimes it really gets in your way.

Kevin Pittman has written an blog post on Drupal 8 Internal Caching for Dummies that helps clarify the different types of caching that occur and how to configure them to work to your advantage.

(The advice that had been posted here by Kevin has been removed as it was no where near as accurate as what is in the blog post.)