this post was submitted on 11 Jun 2023
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Asklemmy
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What does ‘horizontally scalable’ mean here? I haven’t come across that before.
This is what I think, but if anyone understands it differently please correct me.
Vertical scalability refers to scaling within a single instance. More users join and they post more content, increasing the amount of disk space needed to hold that memory, network bandwidth to handle many users downloading comments and images at once, and processing power.
Horizontal scaling refers to the lemmyverse growing because of the addition of new instances. The problem in this form of scaling is due to the resources that an instance has to use due to its interactions with other instances. So, you may create a small instance without a lot of users, but the instance might still need a lot of resources if it attempts to retrieve a lot of information (posts, comments, user information, etc) from the other larger instances. For example, at some point a community in lemmy.ml might be so popular that subscribing to that community from a small instance would be too much of a burden on the smaller instance because of the amount of memory required to save the constant stream of new posts. The horizontal scaling is a problem when the lemmyverse becomes so large that a machine with only a small amount of resources is no longer able to be part of the lemmyverse because its memory gets filled up in a few hours or days.
I don't believe this is how it works though.
Let's say your tiny 3 person instance is connected to a big one. I believe it only pulls in content from the communities somebody from the small instance is subscribed too. Correct me if I'm wrong.
That's what they're saying.
Essentially - if someone from the small instance subscribes to a community that has a ton of data (huge post volume, images, whatever), the small instance needs to pull data over from the larger instance. At some point there may be communities that are so large small instances can't pull them in without tanking.
Could that be solved by caching? Can't the smaller instance avoid some duplication?
maybe I phrased that poorly and you didn't understand what I was trying to say. The size of the bigger instance shouldn't matter at all because only data from communities is pulled, that a member of the smaller instance is subscribed to. So if the bigger instance has 1000 members or 2 million members wouldn't make a difference. The only thing relevant should be how active the communities are that members are subscribed to.