[nullwasamistake]

We have some pretty vanilla file upload code that needs async. S3 latency is fairly high. If you're uploading a few tiny files per user per second, thread usage gets out of hand real fast.

With a simulated load of ~20 users we were running over 1000 threads.

Several posts in the chain say that 20k+ threads is "fine". Not unless you have a ton of cores. The memory and context switching overhead is gigantic. Eventually your server is doing little besides switching between threads.

We had to rewrite our s3 code to use async, now we can do many thousands of concurrent uploads no problem.

Other places we've had to use async is a proxy that intercepts certain HTTP calls and user stats uploader that calls third party analytics service.

Just sayin it's not that unusual to need async code because threading overhead is too high

[pcwalton]

In what language?

[nullwasamistake]

Java