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Does Lemmy really benefit from Rust? Is code execution speed the bottleneck? (programming.dev)

submitted 2 years ago* (last edited 2 years 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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[–] sznio@lemmy.world 16 points 2 years ago (3 children)

Pulling this out of my ass, but I think the problem might be in Lemmy using websockets.

I feel like supporting 1500 simultaneous users making a request every 10-20 seconds is easier than keeping 1500 websockets alive.

Irregardless, Lemmy does feel very snappy compared to other websites I've had the displeasure of using. Main problem is low robustness in the RPC layer.

[–] binwiederhier@discuss.ntfy.sh 11 points 2 years ago

I maintain and host ntfy.sh, an open source push notification service. I have a constant 9-12k WebSocket and HTTP stream connections going, and I host it on a two core machine with an average load average of less than 1. So I can happily tell you that it's not WebSockets. Hehe.

My money would be on the federation. Having to blast/copy every single comment to every single connected instance seems like a lot.

[–] 14specks@lemmy.ml 4 points 2 years ago (1 children)

They're gonna move away from we sockets within a couple of weeks, from what I hear

[–] binwiederhier@discuss.ntfy.sh 2 points 2 years ago

That's a good move IMHO. Honestly I don't want my UI to randomly shift down when new messages come in from syncing with another instance.

The right move would be to make a page that renders once and then only updates when you refresh the page. And then use web push for message notifications.

[–] kaba0@programming.dev 1 points 2 years ago

Wait — it uses websockets for each and every user??! That’s just completely insane and of course it will fail to scale! There is zero reason for that, have specific live threads with websockets where it makes sense (though that is only mostly a one-way communication so even there it is an overkill), but for mostly static content it is just insanely inefficient.. surely I’m more than fine with that upvote appearing a minute later and not in “real time”!