2025 was a big year for Bluesky decentralization. You might have heard of several independent Bluesky alternatives, like Blacksky, Northsky, and Eurosky. You might also have heard that these are nontrivial efforts, requiring significant development work and expensive computing resources. I'd like to dig into the second of those topics.
Well, for starters, there isn't just one Following feed. There's forty million of them. Every user's Following feed is unique.
They're difficult to compute on demand too. Users might follow tens of thousands of accounts, or a single account the user follows might post hundreds of times per hour. And users notice when their timelines don't update quickly. Dealing with this scale is a difficult problem. Bluesky handles it by making the Following feed lossy - rather than giving a precise chronological feed of every post from a followed account, it sheds load by occasionally dropping posts from rapid posters or from timelines of people who follow thousands of other users. Even with that optimization, the costs are significant.
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I'll let you in on a little secret: ActivityPub has this problem too.
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Depending on how many people you follow, how frequently they post, how long it's been, and how busy the instance you're using is, it could take a long time for your timeline to load. This is because Mastodon stops updating timelines for infrequent users. This lets a Mastodon server avoid the costs of keeping timelines up to date for users who don't use the app very much. It comes at a cost though: users who return to Mastodon after taking time away from it are much more likely to bounce off the app permanently if their returning experience starts poorly. The UX factor here is significant, and often unnoticed by power users.
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There's no reason in principle that the strategies chosen by Mastodon wouldn't work for ATproto. The reason they haven't been employed much is that broadly speaking, most Bluesky users want a global view of the network. We like that search works globally without much issue, that it doesn't matter what PDS you're using, and that your choice of client and host is invisible to others.
From the article:
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