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> At what scale(in terms of number of users or server load) would choosing async based web frameworks over traditional web frameworks like Django/Pylons make sense?

Using async makes sense where you want to handle 100s/1000s of long-open connections (websockets for instance). Spawning a lot of threads/processes can be very expensive, and will lead to suboptimal QoS.

> While using async is much easier with the new async/await syntax compared to traditional async solutions like twisted, tornado etc., a lot of popular database connectors and ORMs do not support async currently.

Good news is that you can have most of your application written in Django (or other traditional web framework), using async to implement specific API endpoints.