There's no cap on the number of HTTP fetches being run at a time

[ChillyCider]

We need a way to coordinate between gunicorn/uWSGI/etc. workers to make sure only 1 fetch operation is ever being performed at a time.

Maybe we can leverage our SQLite cache?

Otherwise, we might have to resort to an external solution. (I'd prefer not to do this, because I like how this repo is a self-contained and complete WSGI app)