I've messed with async on JVM. In my experience, it doubles speed at most for CRUD apps with heavy DB access. Async is only useful if you're thread starved, and

I've messed with async on JVM. In my experience, it doubles speed at most for CRUD apps with heavy DB access. Async is only useful if you're thread starved, and most DB calls are fast enough that it never happens. The one place it makes a huge difference is when you're waiting on other, possibly slow, services like third party REST calls. If you have 100 threads and each call takes 1000ms you will run out of threads at 100 req/sec which is quite low for the JVM. Using async in these situations allows thousands of threads to be paused while your 100 still do work, allowing you to handle maybe 10k req/sec even with a slow partner service. A lot of JS programmers don't understand the relation between thread starvation and async, they act like async is magic. If you're not thread starved (everything you do is pretty quick) then async is useless