I doubt I will forget the time I first booted up an Elixir Phoenix server and got something like `[info] Sent 200 in 409µs` and stared at that `µs` for a while before it dawned on my that that was the symbol for microseconds.

I was so used to 20-40ms that I couldn't even comprehend that it could be 80x faster. A year later since playing around in Elixir's world, and I'm still just so impressed by its speeds.

Yeah. It's really something.

Recently I started writing a bunch of tests for a Phoenix application for my first Phoenix app.

After a day of hacking around and learning as I go I had 63 tests of which 57 of them are full blown controller tests where a good amount of those tests are dealing with a "current user" and reading / writing things from a database. I'm even using a "Faker" library to generate fake data for all of the DB attributes.

The entire test suite runs in 600ms. That's 600ms for ~60 controller tests from start to finish. That's in a worst case scenario too where the code is on a non-SSD and that code is volume mounted into a Docker container on Windows while I use WSL.

Sometimes things work so fast that I'm actually worried it's not doing what I think it's doing, but then I run --cover and see that I have 95%+ test coverage on the things I care about, so that code is getting reached.

20-40ms with what language and implementation?

Elixir is pretty slow tbh, like 3-10x slower than Java / C# / Go. Immutability / message passing is very heavy.

It's all relative. Plenty people come from Node, Ruby, and Python.

Coming from the Go! world, I view Elixir is trade of speed for OTP out the box niceness. But comparing Elixir to Node, then you're just gaining speed and stability.

And it keeps going -- I very frequently see Go criticized for slowness by C, C++, and Rust developers. It is all about the usecase, which is why I find this topic so interesting. It's one of the few situations Elixir mid-level speed is actually a real world problem.

I get your point. Even without message passing, just in process calculation in Erlang/Elixir is also pretty slow compared to Java.

But in the domain of Web programming, scheduling efficiency is much more important than the speed of execution. If it is a huge batch operation on a single machine, Erlang/Elixir would be terrible.

Similarly, for React there's fiber mechanism -- it's worse according to benchmark, while the user would get a better experience due to a better schedule.

Yeah for numerical stuff but for network stuff which Erlang and its VM was created for it's great for web application. Having the option to write Rust, C, etc.. with NIF is a good compromise.