New in AR 7: https://rubyonrails.org/2021/12/15/Rails-7-fulfilling-a-vision

Asynchronous Query Loading
When you have a controller action that needs to load two unrelated queries, you can now do it concurrently through Relation#load_async. If you have three complex queries that each take 100ms, you'd have to spend 300ms executing them one by one before. Now you can run them in parallel, spending only a total of 100ms on the set.

https://github.com/rails/rails/pull/41372