Fedigrow

Basically, the way Lemmy is designed, each instance has to tell each other instance what its users did (where relevant—no need to send to aussie.zone a post made in a community that there are 0 aussie.zone subscribers, for example). That includes posts, comments, and upvotes. And the way it's designed, the originating server (in this case, LW) has to send it to the receiving server (AZ), then the receiving server sends a confirmation back, and then the originating server can send the next one.

Because LW is hosted in Germany, and AZ in Australia, there's a minimum amount of time thanks to the physical constraints of sending signals over that long distance. And double that because it's a return trip, and a small amount more for processing time. It ends up measuring in the hundreds of milliseconds. Which leaves you with a maximum of a few hundred thousand actions sent from LW to AZ per day. If LW users are doing more than this, then the delay will slowly grow. If they send less, the delay will shrink, or remain at near 0.

Now, the most recent version of Lemmy actually lets you set it so that instead of sending just one at a time, you can have multiple threads, so you're sending multiple at a time. But LW only upgraded to this version a few days ago, and they didn't turn on this feature when they did so.

Afaik only one item (post/comment) is synced at a time. So if there is a lot of latency between the instances, new content is produced faster than can be synced. But I'm sure someone will link the GH issue if I'm wrong

if the requests are all serialized, if the ping time is like 300ms, and if each request takes like 100ms of CPU time

that means you only need 648,000 actions in queue to equal 3 days

when you consider that even upvotes/downvotes of posts/comments count as actions, I could see it happening

but the queue isn't completely serialized anymore, so maybe this number is still a bit unbelievable (EDIT: seems like LW has not yet enabled the feature for parallel sending)

i don't know if there's any prioritising of types of actions, eg. posts are given higher priority than comments which is higher than up/down votes but when I made posts on lemmy.world I'd get an initial wave of upvotes from other instances and then like 12 hours later a lot of upvotes from lemmy.world users

Yup, exactly so. I'll often notice a reply to one of my comments from a LW user will only show up in my inbox about 3 days later.

Ironically, the whole Lemmy activity makes it to you, just three days later

It should have. The backend added parallel syncing since a few versions back. By all accounts it should be going down.

they're using my federation exporter as data source.

it's just scraping the federation api every 5 min for each included instance and then visualizing that.

@[email protected] is the owner of those dashboards