Oh wow, I never knew Klarna uses BEAM. I always thought BEAM is vastly underrated and it's even hard for me to convince clients of showing how powerful it (Elixir/BEAM) really is, especially when they're already on something like NodeJS. This will be a nice reference to use in conversations with future prospects.

I'm interested to see how this goes, I find it difficult to convince anyone to change from the herp-derp status quo.

One of the early investors worked for Ericsson on Erlang.

Klarna was one of the biggest Erlang shops in 2010s. Then there was some turmoil, but their main system is still in Erlang

To add on to your statement that the BEAM is vastly underrated, it's the only runtime that I know of that has enabled multiple small sub 50 people teams to scale to millions of daily active users.

There will be winners in this new AI age, and they will be the ones that are technically better, rather than the most popular or convenient for software engineers

I use Elixir (BEAM-based), with LLMs daily, on a fast growing site (current pace is 5 billion HTTP queries per year on a single front node).

Elixir is well handled by LLMs at this point, and we keep the “easy to scale and maintain” aspect (operational characteristics of the runtime are very good).

I can safely say that total cost of ownership is excellent.

I think that's the first time I see someone use qpy...

Fair enough! That’s how we track growth, it’s easier to communicate to state sponsors.

Roughly 14M per day, but growing 2.5 to 3 on a YoY basis.

My point stands though: much more serenity in ops with that growth, and LLMs do work nicely, especially when most of the code is stateless by language design.

Being generous... That's about 10k/s? So you're just in range of the C10k problem that OTP was built to overcome?

~160 req/s on average, higher peaks. Not trying to impress anyone though, my point was that LLMs work perfectly fine on an Elixir codebase, and that we get future-proof ops on a single node with zero issues. In my experience, it has been easier than with any other stack I've tried.

To be fair, Erlang runtime semantics (cooperative "async threads") never needed changing to tackle C10k problem, they got that right as part of the early designs before C10k was even on the tasble.

Everyone else just moved towards the same kind of cooperative thread runtime semantics (even if the lingo differs, async in C#, callbacks first, then async in NodeJS, virtual threads in Java, async in C++ and so on).

I think an interesting historical tidbit is that Java actually had M:N threading in early versions (1.1, 1.2, 1.3?) that got ripped out because it was deemed complex and error-prone since people back then often did native bindings naively (And perhaps file/socket API's were less complete?) only for them to reintroduce it again in Java 20 I think it was under the virtual threads name?

> I think an interesting historical tidbit is that Java actually had M:N threading in early versions (1.1, 1.2, 1.3?)

Yeah, they called that “green threads”. https://en.wikipedia.org/wiki/Green_thread

[delayed]

> Cooperative scheduling is based on the programmer releasing control manually (much like manual memory management) or having yield points baked into the language, often at function calls or IO events. Processes on BEAM can be preempted, they're allotted a number of "reductions" and when those are exhausted, the process is preempted (the process may also yield earlier).

BEAM is actually cooperative. In userspace, function calls and IO (receive and !) are yield points, and reduction count is simply the number of function calls you're allowed. Something something Computer Sciencey reduction basically means function call.

It just feels preemptive because as a functional language, you have to call functions all the time. Your loop becomes

   loop(I) -> loop(I + 1).

And that will yield once it calls itself enough times.

Native code (NIFs, BIFs, and drivers) has to count reductions and/or yield explicitly.

You can easily hog scheduler threads in native code that does significant computation or does i/o without using the runtime facilities; most people who write NIFs will mess it up at least once, I certainly have. It's much harder to do in userspace code, but if you fully unroll a very large loop that does not call functions or anything else that can yield, you can do it; I don't see how this would happen without specific intent, I've never run into it, but it's possible.

A blocked scheduler can be vaguely fine or terrible depending on how long it stays blocked and what the system is up to. Often it won't be terrible until you do something that needs all schedulers to synchronize, such as operations around code loading, but you can probably wedge the whole BEAM if you try.

My recollection is that M:N ("green") threads were pulled out because in the absence of a runtime that can guarantee a thread is never blocked, you essentially have to reintroduce all the complexity of an OS scheduler without the benefits of OS-wide context.

"Project Loom" spent much of its time (AFAICT) figuring out how to make every Java system-level API non-blocking without breaking backward compatibility. The only one they didn't get to for the initial release was Java's "interesting" built-in `synchronized` object monitor construct.

10k requests/sec is not really the same thing as the C10k problem which is 10k concurrent connections. You might serve much more or less than one request per second per connection, so req/s and conncurrent connections are not really related.

I also wouldn't say OTP was built to overcome the C10k problem. It is a very good solution for lots of concurrent connections (with a suitable OS), but OTP was built to manage concurrency needs in the context of telephone switches. The constraints chosen to meet those needs does work (very) well to meet the challenges of large numbers of concurrent IP connections, but I wouldn't say it was built to overcome those challenges.

The important metrics is peak requests per second. 14M / day sounds impressive, but it’s only a sustained 160 per second which literally any language and framework can handle on the lowest end hardware.

Sure, peaks are much higher. But a good part of it is reverse proxying with in-memory caching and locking, which I've implemented in several stacks over the years, and many struggle with it (I have been paid to do comprehensive benchmarks on the topic). On the BEAM it's a non-event.

Only if users are nice and spread the load evenly over the day, but they are never so considerate.

Sure, that's why I highlighted peaks as a more important metric than average. Even an order of magnitude higher peaks over the average is still fairly trivial, compared to where BEAM shines. Maintaining hundreds of thousands of concurrent long-lived connections per server is what it excels at, but also not something that's relevant to 99% of web apps out there.

Elixir is perfect for the ai age as it allows you to move a lot of orchestration safely into the application layer.

All 3GL languages are looser in the AI age, beyond formal verification tooling.

I have done several experiments where, the only difference are a couple of paragraphs describing the technology stack for the AI tools.

Hardly any different than changing the target CPU architecture on a compiler output.

Quite sad, as now the fun of why language X instead of Y is gone.

> I have done several experiments where, the only difference are a couple of paragraphs describing the technology stack for the AI tools.

The differences emerge as the project goes on. Comparing feature velocity and defect count is difficult unless your experiment is to build the same project over a long timeframe across several languages. Then winners would indeed emerge, but then that's only in the context of whatever domain said project is tackling. For instance, if concurrency or infrastructure isn't a large part of the complexity, BEAM languages might not confer much benefit.

> BEAM languages might not confer much benefit.

Immutable value languages like BEAM langs are probably useful too, the LLM doesn't have to guess whether a value passed into a function will get mangled by the callee

We used to do brilliant technical stuff to get to the moon. Now we do technically brilliant stuff to commit technically-not-usury.

Progress!

I love Erlang, Elixir, and BEAM by extension. Lucky to have been forced to learn it at KTH.

Perhaps github should read it

Why? Historically they're mostly a Ruby shop.

Right, then a 15ms pause for them is just a method lookup :)

thank you. I've not had time to learn Erlang but always been intrigued by beamp + otp. now with llms I might have a chance to see what's possible

Life in Sweden is a series of moments between fika:)

Did he write the book? Because he didn't write this post.

just picked up a copy

I'd been looking for an excuse to build something in Elixir pretty much since the language was released, and in just the past year and a half I've had the good fortune of getting to use it to build an in house AI agent orchestration system and it's been an absolute pleasure

I've been building with Elixir for the last 5 years, and comparing to Python or NodeJS - it's a breath of fresh air. Such decent developer experience, so easy to understand how your system works because of actors and well-defined primitives. If you haven't - you definitely should give it a try!

In an AI era I feel like the tiny amount of Elixir code in comparison with other languages, but all that code having higher signal to noise ration vastly contributed to how good LLM-written Elixir code is. Especially in a well-maintainted codebase that relies on a decent db schema and Oban.

I think the new typing system will also help immensely. LLMs do like their nice clear error messages

The second edition is out now. https://happihacking.com/resources/the-beam-book/