On BEAM, running 10,000 lightweight processes is normal. Phoenix is designed so that every incoming http request is its own lightweight process.

How does one manage that number of lightweight processes? The runtime’s scheduler keeps track of every single process so nothing is orphaned. It is preemptive, so no lightweight process can starve out another (though there are some exceptions).

They can also suspend cheaply, as such, works well with async io.

The closest thing to this are the new virtual thread feature of recent Java. I don’t think Java has the same kind of properties that will allow it to manage it as well as BEAM. There is a lot more to Elixir than being able to use all the cores.