this post was submitted on 01 Jul 2023
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I already get rate-limited like crazy on lemmy and there are only like 60,000 users on my instance. Is each instance really just one server or are there multiple containers running across several hosts? I’m concerned that federation will mean an inconsistent user experience. Some instances many be beefy, others will be under resourced… so the average person might think Lemmy overall is slow or error-prone.

Reddit has millions of users. How the hell is this going to scale? Does anyone have any information about Lemmy’s DB and architecture?

I found this post about Reddit’s DB from 2012. Not sure if Lemmy has a similar approach to ensure speed and reliability as the user base and traffic grows.

https://kevin.burke.dev/kevin/reddits-database-has-two-tables/

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[–] [email protected] 22 points 2 years ago (2 children)

Bigger instances will indeed run multiple copies of the various components, it's pretty standard software in that regard.

Usually at first that will start by moving the PostgreSQL database to its own dedicated box, and then start adding additional backend boxes, possibly adding more caching in front so that the backend doesn't have to do as much work. Once the database is pegged, the next step is usually a write primary and one or more read secondaries. When that gets too much, you get into sharding so that you can spread the database load across multiple servers. I don't know much about PostgreSQL but I have to assume it's better than MySQL in that regard and I've seen a 1 TB MySQL database in the wild running just fine.

I think lemmy.world in general is hitting some scalability issues that they're working on. Keep in mind the software is fairly new and is just being truely tested at large scale, there's probably a ton of room for optimization. Also lemmy.world is still on 0.17 and apparently 0.18 changed the protocol a lot in a way that makes it scale much better, so when they complete that upgrade it'll probably run a lot better already.


The part that worries me about scalability in the long term is the push nature of ActivityPub. My server is already getting several POST requests to /inbox per second already, which makes me wonder how that's gonna work if big instances have to push content updates to thousands of lemmy instances where most of the data probably isn't even seen. I was surprised it was a push system and not a pull system, as pull is much easier to scale and cache at the CDN level, and can be fetched on demand for people that only checks lemmy once in a while.

I need to start digging into Lemmy's code and get familiar with the internals, still only a couple days in with my private instance.

[–] [email protected] 2 points 2 years ago

I don’t have a coding background but this was very informative. Thanks for sharing

[–] [email protected] 0 points 2 years ago* (last edited 2 years ago) (1 children)

The implementation as far as I understand it is plain stupid. It prevents small instances from participating at any significant scale and seems happy to just drop data over the wire without reconciling. Seriously amateurish.

[–] [email protected] 1 points 2 years ago

I'm not sure about the data being dropped, my instance was misconfigured for a day or two, and as soon as I fixed it, the data came right in. Instances repeatedly trying to push data to my instance is what clued me in that something was missing from my NGINX config. It backfilled pretty fast.

Although I wouldn't mind if there was a fallback pull mechanism to remediate failed pushes.