You got a lot of heat in this discussion, but let me be one of the few to applaud you for actually making a proposal. Saying No is easy, but suggesting something and writing it down and putting it out there is hard.

I am a Principal Engineer by trade, and i do what you did here all the time. I put out suggestions to my team and let them absolutely wreck it. This is how you advance and enhance your idea. Listen and learn from the feedback and suggest another thing based on what you have learned. Rinse and repeat.

That's how you get to a great proposal. Keep at it. Well done.

But, just to bring some math in- with the current full-mesh federation model, assuming 10,000 instances-

That will require nearly 50 million connections.

Each comment. Each vote. Each post, will have to be sent 50 million seperate times.

Well your whole premise is just utterly wrong.

The way federation actually works:

A user on lemmy.ml subscribes to a community on lemmy.world. Say, !funny@lemmy.world

Assume that this user is the first lemmy.ml user to do so - basically what happens is the lemmy.world community sees that a member of a never before seen instance just subscribed. !funny@lemmy.world then adds lemmy.ml to its list of instances it needs to tell whenever something happens in the community.

No matter how many users of lemmy.ml subscribe, this only happens once.

Now when a user of sh.itjust.works upvotes a post on !funny@lemmy.world, the sh.itjust.works instance then tells !funny@lemmy.world of this change. It accepts the change, then tells everyone on its list of instances that have subscribers on them.

So essentially, sh.itjust.works talks to lemmy.world, lemmy.world tells everyone else. There is no "full mesh". The instance hosting the community is the "hub", everything else is a spoke.

So if there's 10,000 instances, and they all just so happen to have at least one subscriber to some community, each change will be sent out 9,999 times. Your "50 million" premise is just completely wrong and I'm not sure where it's coming from.

Activities aren't sent on every "connection" in the network in the current model. There isn't indirect transmission nor polling so even though there's a theoretical 50 mil connections in the scenario you gave, any one activity will already only be sent up to 10k times. That's why instances require TLS and being internet accessible, so they can receive direct communication. I agree with you that there's some difficult scaling issues with federation but your representation of it is inaccurate.

The same problem can also be solved with signed messages, like the HTTP Signatures used by Mastodon and most of the other microblogging fedi servers. Signatures allow a message to flow peer-to-peer instead of requiring a direct connection. You would only need a connection when actively interacting with a post on another instance, and its very unlikely that all 10K instances would be interacting with each other. Most likely, the network will consist of smallish groups of loosely-related instances plus a few giant servers that can handle the load of being popular.

Other people in the thread have already made this point: even with a full mesh network, the number of remote calls made for a single activity is equal to the number of instances subscribing to that activity (plus one if the activity originates from an instance that's not the host of the activity).

A hub/spoke model doesn't change this, it just moves the load from the host instance to the hub. The number of connections is still the same: if N instances need to receive the activity, N calls will have to be made. If anything this adds 1 more call from the host instance to the hub.

Even peer-to-peer distribution of activities, mentioned by @hazelnoot@beehaw.org, wouldn't actually change the amount of calls being made. You still have N servers that have to receive the activity, so you need at least N calls overall. What this would do is redistribute the load better over instances, so the host doesn't have to make all N calls. It would definitely be an improvement, but it would not be easy to implement successfully, and it would almost surely break ActivityPub compatibility.

The only thing I can think of that would actually reduce the overall network load, though, is batching: sending multiple activities/updates together in a single message. AFAIK this is not supported by ActivityPub, though, so implementing it would mean breaking compatibility, and also implementing an entirely updated version of the protocol (which is a massive undertaking).

Nice but it kinda breaks the point of federation - who's running the hubs? If it's a company, then nice, we're back to appeasing our corporate overlord. I

If it's a secondary federated system, nice now you're just needlessly complicating things, as anyone could create a hub - you could end up with a lot of single spoked hubs.

In your proposal, who would run these hub servers?

Is this accurate on how it works? My assumption was a user would have to be subscribed to a remote community on their local instance for that local instance to pull posts/votes/comments from the remote instance. It's not like everything is replicated everywhere.

I'll be the odd one out and say I support this model but for other reasons than the technical limitations and scaling problems involved. For me it's more about trying to establish a tighter ring of trust and enable easier user onboarding as the hub could serve as the primary identity store for users on multiple instances.

I mentioned it in some chat earlier, but I think that the Beehaw.org moderation model, goals, and philiosophy serves as an excellent starting point for like-minded communities to build out the hub-and-spoke. It would also give them greater flexibility in maintaining the health of their corner of the fediverse by centralizing identity with them.

This model would, of course, not stop others from creating their own hub and spoke and would break apart the fediverse a bit, so I suppose there should be a way for "hubs" to talk to eachother in a way that resembles what we have now.

From a blocking bad actors standpoint (I'm still upset about Captcha getting removed even if it's a technically inferior solution), it would be far easier to have fewer hubs to need to blacklist/whitelist than having to do it for each individual instance.

I guess to go a bit further, if Lemmy could support both "modes" (as in it can be configured to be hub and spoke as either the hub or spoke, as well as retain the existing functionality for those who don't want a hub) that would be ideal.