[vc8f6vVV]

Not exactly sure how async in Python works, but if its runtime is non-preemptive and single-threaded (i.e. based on yield), then congratulations, you reinvented Windows 3.1! Those who are old enough to be "lucky" to use it, remember that the damn thing could hang the whole OS if your application was careless enough to block and not yield. Also "slow" is relative, if you create a thread to do DB query, thread creation is a way faster than any DB request, so not sure why it's slow. Never had problems with Ruby threads even though Ruby doesn't have a mechanism to create a thread pool (didn't have? it's been some time since I worked with Ruby). Java & Scala, OTOH are using thread pools, even multiple variations of them, so the thread startup time doesn't matter. In any case you are talking about I/O, in which case neither thread startup nor context switching matters.