In the last weeks Lemmy has seen a lot of growth, with thousands of new users. To welcome them we are holding this AMA to answer questions from the community. You can ask about the beginnings of Lemmy, how we see the future of Lemmy, our long-term goals, what makes Lemmy different from Reddit, about internet and social media in general, as well as personal questions.
We’d also like to hear your overall feedback on Lemmy: What are its greatest strengths and weaknesses? How would you improve it? What’s something you wish it had? What can our community do to ensure that we keep pulling users away from US tech companies, and into the fediverse?
Lemmy and Reddit may look similar at first glance, but there is a major difference. While Reddit is a corporation with thousands of employees and billionaire investors, Lemmy is nothing but an open source project run by volunteers. It was started in 2019 by @dessalines and @nutomic, turning into a fulltime job since 2020. For our income we are dependent on your donations, so please contribute if you can. We’d like to be able to add more full-time contributors to our co-op.
We will start answering questions from tomorrow (Wednesday). Besides @dessalines and @nutomic, other Lemmy contributors may also chime in to answer questions:
Here are our previous AMAs for those interested.
The stack is great, I wouldnt want to change anything. Postgres is very mature and performant, with a high focus on correctness. It can sometimes be difficult to optimize queries, but there are wizards like @dullbananas@lemmy.ca who know how to do that. Anyway there is no better alternative that I know of. Rust is also great, just like Postgres it is very performant and has a focus on correctness. Unlike most programming languages it is almost impossible to get any runtime crashes, which is very valuable for a webservice.
The high performance means that less hardware is required to host a given number of users, compared to something like NodeJS or PHP. For example when kbin.social was popular, I remember it had to run on multiple beefy servers. Meanwhile lemmy.ml is still running on a single dedicated server, with much more active users. Or Mastodon having to handle incoming federation activities in background tasks which makes the code more complicated, while Lemmy can process them directly in the HTTP handler.
Nevertheless, scaling for more users always has its surprises. I remember very early in development, Lemmy wasnt able to handle more than a dozen requests per second. Turns out we only used a single database connection instead of a connection pool, so each db query was running after that last one was finished, which of course is very slow. It seems obvious in retrospect, but you never notice this problem until there are a dozen or so users active at the same time.
With the Reddit migration two years ago a lot of performance problems came up, as active users on Lemmy suddenly grew around 70 times. You can see some of that in the 0.18.x release announcements. One part of the solution was to add missing database indexes. Another was to remove websocket support, which was keeping a connection open for each user. That works fine with 100 users, but completely breaks down with 1000 or more.
After all there is nothing I would do different really. It would have been good to know about these scaling problems earlier, but thats impossible. In fact for my project Ibis (federated wiki) Im using the exact same architecture as Lemmy.
It’s great to hear things mostly worked out. Stuff like scaling bottlenecks is definitely tricky to catch until you have serious loads on the system, but sounds like the fixes very mostly trivial validating overall design. It also looks like you managed to get a way with a fairly simple stack by leveraging Postgres and Rust. I’ve had really good experience with using pg myself, and really don’t see a point in using anything else now. You can use it both as a relation db and a document store, so it’s extremely flexible on top of being highly performant. Keeping the stack simple tends to be underappreciated, and projects often just keep adding moving pieces which end up adding a lot of overhead and complexity in the end.