[ajross]

> The classic use case for async was applications with extreme I/O intensity, like high-end database engines. If designed correctly it is qualitatively higher performance than classic multithreading.

FWIW, I'm not aware of any high end database engines that make significant use of async code on their performance paths. They manage concurrent state with event loops, state machines, and callbacks. Those techniques, while crufty and too old to be cool, are themselves significantly faster than async.

Async code (which is isomorphic to process-managed green threads) really isn't fast. It's just that OS thread switching is slow.