FOSSDLE PieFedThe two most upvoted comments on any Lemmy instance are on Feddit.dk, but you won't see them on your own instance
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SorteKanin
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I recently discovered an interesting (and somewhat disappointing, as we'll find later) fact. It may surprise you to hear that the two most upvoted comments on any Lemmy instance (that I could find at least) are both on Feddit.dk and are quite significantly higher than the next top comments.
The comments in question are: 1. This one from @bstix@feddit.dk with a whopping 3661 upvotes. 2. This one from @TDCN@feddit.dk with 1481 upvotes.
These upvote counts seems strange when you view them in relation to the post - both of the comments appear in posts that do not even have 300 upvotes.
Furthermore, if you go on any instance other than Feddit.dk and sort for the highest upvoted comments of all time, you will not find these comments (you'll likely instead find this one from @Plume@lemmy.blahaj.zone).
Indeed, if you view the comments from another instance (here and here), you will see a much more "normal" upvote count: A modest 132 upvotes and a mere 17 upvotes, respectively.
What's going on?
Well, the answer is Mastodon. Both of these comments somehow did very well in the Mastodon microblogging sphere. I checked my database and indeed, the first one has 3467 upvotes from Mastodon instances and the second one has 1442 upvotes from Mastodon instances.
Notice how both comments, despite being comments on another post, sound quite okay as posts in their own right. A Mastodon user stumbling upon one of these comments could easily assume that it is just another fully independent "toot" (Mastodon's equivalent of tweet).
Someone from Mastodon must have "boosted" (retweeted) the comments and from there the ball started rolling - more and more people boosted, sharing the comments with their followers and more and more people favorited it. The favorites are Mastodon's upvote equivalent and this is understood by Lemmy, so the upvote count on Lemmy also goes up.
Okay, so these comments got hugely popular on Mastodon (actually I don't know if 3.4k upvotes is unusual on Mastodon with their scale but whatever), but why is there this discrepancy between the Lemmy instances then? Why is it only on Feddit.dk that the extra upvotes appear and they don't appear on other instances?
The reason is the way that Mastodon federates Like objects (upvotes). Like objects are unfortunately only federated to the instance of the user receiving the Like, and that's where the discrepancy comes from. All the Mastodon instances that upvoted the comments only sent those upvotes directly to Feddit.dk, so no other instances are aware of those upvotes.
This feels disappointing, as it highlights how Lemmy and Mastodon still don't really function that well together. The idea of a Lemmy post getting big on Mastodon and therefore bigger on Lemmy and thus spreading all over the Fediverse, is unfortunately mostly a fantasy right now. It simply can't really happen due to the technical way Mastodon and Lemmy function. I'm not sure if there is a way to address this on either side (or if the developers would be willing to do so even if there was).
I personally find Mastodon's Like sharing mechanism weird - only sharing with the receiving instance means that big instances like mastodon.social have an advantage in "gathering Likes". When sorting toots based on favorites, bigger instances are able to provide a much better feed for users than smaller instances ever could, simply because they see more of the Likes being given. This feels like something that encourages centralization, which is quite unfortunate I think.
TL;DR: The comments got hugely popular on Mastodon. Mastodon only federates upvotes to the receiving instance so only Feddit.dk has seen the Mastodon upvotes, and other instances are completely unaware.
Your instance doesn't pull the upvotes from other instances. That would not be scalable. How would it know when to pull again, to see new upvotes? When would it stop pulling periodically? Never? And you'd have to do this for every single post and comment everywhere.
No, instead ActivityPub uses a push mechanism here. So any new activity is pushed out to the ones that are deemed relevant to know about the activity. Any other instances are unaware.
Pulling the data when a user requests a post/comment (with a cooldown/cache for popular posts) isn't any more or less scalable than feddit.de pushing the same data whether it's been requested or not. If anything, I'd think pushing data when it's not necessarily needed would be *less* scalable.
But if it has to be a push model, why doesn't feddit.dk push the votes it knows about along with the rest of the data?
That would definitely be less scalable. That would entail pulling every single time a user views a post or comment. That's simply not feasible. There are far, far more views of content than there are posts, comments and votes.
Also what about stuff that isn't seen? What if nobody is logged in or nobody looks at the New sort? You need the votes before you even show the user anything, otherwise you can't sort the votes.
This has been explained elsewhere in the thread, see https://feddit.dk/post/7628338/10255563
True, but that's why I mentioned a cache or cooldown. Once every two minutes is plenty, unless Lemmy really blows up and we have hundreds of instances trying to fetch a very popular post.
You have a point about new sort, but you could approximate it by sorting what's known to an instance. It's not ideal, but it's at least something. Maybe it would make sense to push just that feed, or to fetch a subset periodically.
I read that comment tree, but it doesn't answer my question. If someone on Mastodon likes a post on feddit.dk, I don't see any reason feddit.dk can't communicate that to lemm.ee when I go look at it.
That won't work, because it would have to be once every two minute for every single comment and post forever.
I have no idea what you mean by this - you can't fetch a feed, that's not at all how the data is organised.
The problem is this: How does lemm.ee know that the like that feddit.dk claims is from mastodon.social actually is from mastodon.social? What prevents feddit.dk from just fabricating a like from mastodon.social? Currently there is no nice mechanism for authenticating such a forwarded like. A malicious instance could send loads of likes claiming they come from other instances.