> The only modern web problem that Elixir isn't ideally suited for is heavy number crunching.
I would caveat that in a couple of ways.
First, suppose you have a web app where some requests involve heavy number crunching and others don't. In web frameworks where 1 request ties up 1 OS thread, a burst of heavy requests could gobble up all your available connections. Phoenix would use one cheap BEAM process per request, and the BEAM's preemptive scheduler would ensure that other requests are answered in a timely way and that all the heavy ones continue to make steady progress. So although the heavy requests might be completed more slowly than in another language, the overall system would remain more responsive.
I would caveat that in a couple of ways.
First, suppose you have a web app where some requests involve heavy number crunching and others don't. In web frameworks where 1 request ties up 1 OS thread, a burst of heavy requests could gobble up all your available connections. Phoenix would use one cheap BEAM process per request, and the BEAM's preemptive scheduler would ensure that other requests are answered in a timely way and that all the heavy ones continue to make steady progress. So although the heavy requests might be completed more slowly than in another language, the overall system would remain more responsive.
Second, if you have need for heavy computation or data structures that work better with mutability, it's possible to (eg) use Rustler (https://github.com/rusterlium/rustler) to implement that part in Rust. See https://github.com/rusterlium/rustler for a story about doing this.