How small can ATproto get, really? - Unfolding Diagrams

"What makes Bluesky expensive?", asks Jacqueline.

• not the user data: a "PDS... is little more than a JSON-returning webserver wrapped around a SQLite database. A single PDS on a raspberry pi can host and serve data for tens of thousands of users"
• nor the relay, which can "run just fine on a raspberry pi... [with] beefy storage drive (a dozen or two terabytes)... entirely within reach of a hobbyist."
• the appview? nope, as shown by "

Red Dwarf... Bluesky client that works entirely client-side, with no AppView server ... by 1) talking to PDS instances directly, 2) querying the Constellation microservice for links between records, and 3) using the Slingshot edge cache to fetch records"

It's the Following Feed, which Red Dwarf doesn't offer, and which " accounts for half of Bluesky's entire production workload", because there are 40million of them, and each is "difficult to compute on demand ... Users might follow tens of thousands of accounts", each of which "might post hundreds of times per hour", which is why Bluesky's is a bit lossy, "occasionally dropping posts from rapid posters or from timelines of people who follow thousands of other users".

Interestingly, "ActivityPub has this problem too", which is why "Mastodon stops updating timelines for infrequent users". This discourages occasional users, and is unnoticed by power users. This cost is lower for the many instances which don't see the whole network, but it means large servers cost more and the overall UX is poor, particularly on small servers. So it makes Mastodon more suitable for cozyweb, which is legitimate: "many [users] want to run a small semi-isolated stack of social media servers for just them and their friends... It's certainly a lot more interesting than just throwing everyone into a Discord server".

Could ATproto do the same? "Blacksky, Northsky, and Eurosky are large efforts because ... They're meant to be global, full-network views of all forty million ATproto accounts that are fully independent of Bluesky. There is no cheap way to do that".

But if you wanted something cozier, a modded "Red Dwarf that included a server for the Following feed limited to a selected list of invited users ... [with] invite list ... based on a PDS: press a button, deploy a PDS you can invite people too, a Following feed limited to just the users of that PDS, and a webserver that presents a Red Dwarf-like client app with customizable theming and which can only be logged into by accounts hosted on that PDS. And it could include its own moderation labeler and Ozone instance too."