Lemmy.world inbound federation is about 18 hours behind, and slowly catching up.
Outbound is fine: If you post or comment on something in a lemmy.world community, it will be almost instantly federated to other users, but if they reply to you then it will take 18 hours before you see it.
It was caused by an assumed Kbin bug in combination with a lemmy bug
All other instances seem fine for inbound and outbound federation

This is specifically for lemmy.world content being sent to lemmy.nz, so if your account is on another instance it may not affect you (but might - at it's peak there were 100+ affected instances, and now there are still 20 that haven't recovered).

[–] purrtastic 2 points 8 months ago (1 children)

Sometimes federation seems as wasteful as blockchain…

[–] Dave 1 points 8 months ago (1 children)

Haha well block chain is intended to use as much processing as possible, it's basically doing extra for (almost) no reason as a feature.

At least federation is doing something with each action. Would be nice if they could be batched, though.

I think some of the issue is Lemmy's immaturity. Lemmy.world spends a lot of time sending updates that are rejected because lemmy.nz is still busy with other requests. More mature software like Mastodon will handle concurrent requests and I assume queue them as well.

We also have a little extra problem where we have down votes. Mastodon has likes, but you either receive a like request or an undo like request. Lemmy has additional items where it can be a like, undo like, down vote, undo down vote, and it's possible to also go from upvote to down vote, skipping the undo. This makes it really important the order is right, so you get the right end state. There are people much smarter than I talking in the issue about how to solve the issue, but no clear consensus yet.

[–] Panq 2 points 8 months ago (1 children)

At least federation is doing something with each action. Would be nice if they could be batched, though.

Dumb question: What happens whenever someone spins up a new instance?

[–] Dave 2 points 8 months ago

Nothing, initially.

When a user subscribes to a community on another instance, the user's instance (let's say lemmy.new) asks the community instance (let's say lemmy.world) to send them updates (the instance doesn't get anything for a community where there are no local subscribers).

From this point forward, if lemmy.world is sending out federation activities for that community, it will send the update to lemmy.new as well.

If you're wondering about the years of history on that community, it's not federated to the new instance. The new instance only has the posts grabbed at the point of initial subscription of the first subscriber (a few pages of posts, unsure of the exact criteria), then any going forward. Not the history, which it will probably never have.

I believe you can grab a specific post by taking the URL from the host instance (lemmy.world, in the example) and searching for it on the new instance (lemmy.new), but this would only retrieve that specific post and I believe no comments.

There's no widescale backfilling of previous posts and comments.