Well, I developed and now manage dev for a Rails app that has half a million customers, with holiday demand peak times, etc. I haven't lost a night's sleep in the almost 10 years to the app.

I'm interested in what impracticalities are involved in our threaded deployment of Rails?

How do you get Rails models querying the db to use threads and not block the whole process from accepting other requests?

Take a look into the ActiveRecord connection pool: https://api.rubyonrails.org/classes/ActiveRecord/ConnectionA...

Why isn't it practical?