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Comment on The strenghts and weaknesses of atproto and activitypub.

FundMECFSResearch@lemmy.blahaj.zone ⁨4⁩ ⁨days⁩ ago

For Activitypub, a weakness is that the server has to host all the visible content to the server. So for example if lemmy got really big, and you wanted to host a tiny server but are subscribed to most lemmy comms, your server ends up hosting and fetching a copy of everything posted in these communities, which can add up to A LOT, in terms of network usage, and computational power. (For example see the debacle where an Australian sever (I think aussie.zone) struggled with this and was weeks behind fetching content from lemmy.world since so much content comes from that instance).

This probably would scale pretty terribly if it got anywhere near the size of reddit.

ATProto gives a scalable solution to this (but comes with tradeoffs). Where you can create your own “instance” PDS (Personal Data Server), without hosting all the posts federated to you, since this is hosted by a “relay” which does most of the heavy lifting computationally. So it ends up with a solution that looks more centralised (since there is less incentive to host relays, so fewer relays), but also much more friendly to people who wanna host their own “PDS” and therefore control their data. This is also very helpful with scalability and solves some of the weird federation quirks activitypub has (ie. you can’t see a lemmy community or mastodon account until someone on your instance subscribes or follows it).

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irelephant@lemmy.dbzer0.com ⁨4⁩ ⁨days⁩ ago
Yes, this does help, but atproto as a whole still doesn’t scale well:

In the beginning of our network, we have 26 users, which conveniently for us map to each letter of the English alphabet: [Alice, Bob, Carol, … Zack]. Each user sends one message per day, which is intended to have one recipient. (This may sound unrealistic, but this is fine to do to model our scenario.) To simplify things, we’ll have each user send a message in a ring: Alice sends a message to Bob, Bob sends a message to Carol, and so on, all the way up to Zack, who simply we wrap around and have message Alice. This could be because these messages have specific intended recipients or it could be because Bob is the sole “follower” of Alice’s posts, Carol is the sole “follower” of Bob’s, etc.

Let’s look at what happens in a single day under both systems.

Under message passing, Alice sends her message to Bob. Only Bob need receive the message. So on and so forth.

From an individual self-hosted server, only one message is passed per day: 1. From the fully decentralized network, the total number of messages passed, zooming out, is the number of participants in the network: 26. Under the public-gods-eye-view-shared-heap model, each user must know of all messages to know what may be relevant. Each user must receive all messages.

From an individual self-hosted server, 26 messages must be received.

Zooming out, the number of messages which must be transmitted in the day is 26 * 26: 676, since each user receives each message.

Okay, so what does that mean? How bad is this? With 26 users, this doesn’t sound like so much. Now let’s add 5 users.

Under message passing:

Per server, still 1 message received per user per day. Per the network, it’s 5 extra messages transmitted per day, which makes sense: we’ve added 5 users. Under the public-gods-eye-view-shared-heap model:

Per server: 5 new messages received per user per day.

Per the network, it’s ((31 * 31) - (26 * 26)): 285 new messages per day!

But we aren’t actually running networks of 26 users. We are running networks of millions of users. What would happen if we had a million self-hosted users and five new users were added to the network? Zooming out, once again, the message passing system simply has five new messages sent. Under the public shared heap model, it is 10,000,025 new messages sent! For adding five new self-hosted users! (And that’s even just with our simplified model of only sending one message per day per user!)

Source: dustycloud.org/…/re-re-bluesky-decentralization/

As well as this, if there was a reddit-like atproto AppView, setting up multiple instances of it would still result in the same problems.

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- FundMECFSResearch@lemmy.blahaj.zone ⁨4⁩ ⁨days⁩ ago
  But this is assuming private messages no?
  
  When 99% of the public traffic is on posts that will federate to most servers, this model becomes irrelevant.
  
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  - irelephant@lemmy.dbzer0.com ⁨4⁩ ⁨days⁩ ago
    That’s a good point.
    I think by recipient they meant followers in general.
    
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