this post was submitted on 15 Jun 2023
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Does Lemmy really benefit from Rust? Is code execution speed the bottleneck? (programming.dev)
submitted 1 year ago* (last edited 1 year ago) by Buttons@programming.dev to c/programming@programming.dev
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My first experience with Lemmy was thinking that the UI was beautiful, and lemmy.ml (the first instance I looked at) was asking people not to join because they already had 1500 users and were struggling to scale.

1500 users just doesn't seem like much, it seems like the type of load you could handle with a Raspberry Pi in a dusty corner.

Are the Lemmy servers struggling to scale because of the federation process / protocols?

Maybe I underestimate how much compute goes into hosting user generated content? Users generate very little text, but uploading pictures takes more space. Users are generating millions of bytes of content and it's overloading computers that can handle billions of bytes with ease, what happened? Am I missing something here?

Or maybe the code is just inefficient?

Which brings me to the title's question: Does Lemmy benefit from using Rust? None of the problems I can imagine are related to code execution speed.

If the federation process and protocols are inefficient, then everything is being built on sand. Popular protocols are hard to change. How often does the HTTP protocol change? Never. The language used for the code doesn't matter in this case.

If the code is just inefficient, well, inefficient Rust is probably slower than efficient Python or JavaScript. Could the complexity of Rust have pushed the devs towards a simpler but less efficient solution that ends up being slower than garbage collected languages? I'm sure this has happened before, but I don't know anything about the Lemmy code.

Or, again, maybe I'm just underestimating the amount of compute required to support 1500 users sharing a little bit of text and a few images?

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[–] sekhat@lemmy.temporus.me 1 points 1 year ago* (last edited 1 year ago)

Eh, if by smart pointer you mean Pin. It's not really a smart pointer. It's just a struct that holds onto a particular reference kind. What it holds onto can be a smart pointer, or a mutable reference. Either way, once done, the constraints of the language's ownership and borrowing mean the item that has been Pinned can't be moved.

An item being unable to be moved is pretty important for self referential structures of course, since to self reference, you generally refer to something by some form of pointer inside yourself. If you are able to be moved, your own root address changes and thus the address of anything inside you would be different, which would invalidate your self references.

Pin was quite a clever realization.

However, unfortunately, not all considerations you need to be aware of when using Pin can be enforced by the type system, usually around when you need to Unpin something. And you get that wrong you might end up in a place that would cause Undefined Behavior. Which is why the general advice is, once you've Pinned something, it should stay Pinned.