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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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[–] Espi@kbin.social 48 points 1 year ago (15 children)

I would say that it's extremely unlikely.

Websites in general are never limited by raw code execution, they are mostly limited by IO. Be that disk IO as files are read and written, database IO as you need to execute complex queries to gather all the data to build the user timeline, and network IO to transfer data to and from the user. For decentralized social media like Kbin or Lemmy its even more IO limited as each instance needs to go back and forth to other instances to keep up-to-date data.

Websites usually benefit much more from caching and in-memory databases to keep frequently used data in fast storage.

This is why simple, high level, object oriented, garbage collected languages have become so common. All the CPU performance penalties they incur don't actually affect the website performance.

[–] th3raid0r@tucson.social 2 points 1 year ago* (last edited 1 year ago) (9 children)

In lemmy's case, my perusal of the DB didn't really suggest that the queries would be that complex and I suspect that moving it to a higher performance NoSQL DB might be possible, but I'd have to take a look at a few more queries to be sure.

I wonder if this could be made to work with Aerospike Community Edition...

Obviously it could be more effort than it's worth though.

[–] terebat@programming.dev 22 points 1 year ago

The issues I've seen more are around images. Hosting the images on an object store (cloudflare r2, s3) and linking there would reduce a lot of federation bandwidth, as that's probably cause higher ram/swap usage too.

pict-rs supports storing in object stores, but when getting/serving images, it still serves through the instance as the bottleneck IIRC. That would do quite a bit to free up some resources and lower overall IO needed by the server.

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