For the context: https://feddit.org/post/2374543

TL;DR: Aussie.zone has been experiencing a 7-days delay with LW since quite a long time due to the way Lemmy manages federation, and the distance between LW and aussie.zone.

Lemmy.world is the only one having such delay, even Lemm.ee which is the second most active instance is up-to-date (same for Lemmy.ml with a lot of active communities)

Graphs:

The issue has been solved in 0.19.6 (https://github.com/LemmyNet/lemmy/pull/4623) which hasn’t been released yet.

Explanation by @Nothing4You@programming.dev

lemmy’s current federation implementation works with a sending queue, so it stores a list of activities to be sent in its database. there is a worker running for each linked instance checking if an activity should be sent to that instance, and if it should, then send it. due to how this is currently implemented, this is always only sending a single activity at a time, waiting for this activity to be successfully sent (or rejected), then sending the next one.

an activity is any federation message when an instance informs another instance about something happening. this includes posts, comments, votes, reports, private messages, moderation actions, and a few others.

let’s assume an activity is generated on lemmy.world every second. now every second this worker will send this activity from helsinki to sydney and wait for the response, then wait for the next activity to be available. to simplify things, i’ll skip processing time in this example and just work with raw latency, based on the number you provided. now lemmy.world has to send an activity to sydney. this takes approximately 160ms. aussie.zone immediately responds, which takes 160ms for the response to get back to helsinki. in sum this means the entire process took 320ms. as long as only one activity is generated per second, this is easy to keep up with. still assuming there is no other time needed for any processing, this means about 3.125 activities can be transmitted from lemmy.world to aussie.zone on average.

the real activity generation rate on lemmy.world is quite a bit higher than 3.125 activities per second, and in reality there are also other things that take up some time during this process. over the last 7 days, lemmy.world had an average activity generation rate of about 5.45 activities per second. it is important to note here that not all activities generated on an instance will be sent to all other linked instance, so this isn’t a reliable number of how many activities are actually supposed to be sent to aussie.zone every second, rather an upper limit. for example, for content in a community, lemmy will only send these activities to other instances that have at least one subscriber on the remote instance. although only a fraction of the activities, private messages are another example of an activity that is only sent to a single linked instance.

to answer the original question: the week of delay is simply built up over time, as the amount of lag just keeps growing.

    • OpenStars@discuss.onlineEnglish
      6·
      2 months ago

      Until v0.19.6 (the git link says “federation: parallel sending per instance #4623”), although I’m surprised that they haven’t switched to a package model yet - that must be absolute hell on someone’s network bandwidth to operate a Lemmy instance. Imagine an accidental downvote, then press it again to cancel, then press upvote, altogether counts as 3 separate network traffic packages. In comparison, I would naively guess that e.g. sending a whole minute’s worth of activity would be much more preferable, or at least bundle all the activities together that occurred within the prior second to send at once?

      • ᴇᴍᴘᴇʀᴏʀ 帝@feddit.ukMEnglish
        5·
        2 months ago

        And that’s with everything operating as expected, when things go sideways it can really hammer an instance’s performance.

        It’s why having funded and dedicated developers is critical as they can respond to issues like this and fix it while we are still in the early days.

        • OpenStars@discuss.onlineEnglish
          4·
          2 months ago

          It’s a good thing that nothing of consequence is planned to happen anywhere in the world, especially the USA, like related to politics or anything. Y-y-yeah it’s a good thing there’s nothing like that coming! 😔

    • SpeziEnglish
      13·
      2 months ago

      They have to ship a thumb drive with all federated posts over there every day.

    • Olap@lemmy.worldEnglish
      5·
      2 months ago

      There’s the TCP sliding window to solve this. Just needs done, along with a whole host of other work. I’d donate, but are the original pair any better at sharing work yet?

  • Nath@aussie.zoneEnglish
    3·
    1 month ago

    Oh hey! That’s us!
    We’ve known about this issue since March. OP’s post is a very good explanation of the problem. Lemmy wasn’t designed with one huge instance in mind like this and lemmy.world is the only instance I’m aware of being a problem. Our Kiwi sisters and brothers hacked around the problem five months ago: They set up a server in Finland, slurp up bulk lemmy.world content in batches and then insert that content into their local database. They invited us to share their code to do this, but:

    1. It required us to spend money on a VM in Finland specifically for lemmy.world content - a precedent that made us hesitate.
    2. This is a temporary problem, a new version of Lemmy was meant to come out some months to remedy it. It simply hasn’t been released, yet.

    Had we known in May that this would still be an issue in October, we might have chosen differently.