Lemmy PERFORMANCE CRISIS: popular instances with many remote instances following big communities could stop federating outbound for Votes on comments/posts - code path identified

I spent several hours tracing in production (updating the code a dozen times with extra logging) to identify the actual path the lemmy_server code uses for outbound federation of votes to subscribed servers.

Major popular servers, Beehaw, Leemy.world, Lemmy.ml - have a large number of instance servers subscribing to their communities to get copies of every post/comment. Comment votes/likes are the most common activity, and it is proposed that during the PERFORMANCE CRISIS that outbound vote/like sharing be turned off by these overwhelmed servers.

pull request for draft:

https://github.com/LemmyNet/lemmy/compare/main...RocketDerp:lemmy_comment_votes_nofed1:no_federation_of_votes_outbound0

EDIT: LEMMY_SKIP_FEDERATE_VOTES environment variable

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I have no idea why the file is named "mod.rs", as normal non-admin non-moderator users seem to go through this code path.

this is a rust thing: https://stackoverflow.com/questions/26435102/in-rust-what-is-the-purpose-of-a-mod-rs-file

ok, I figured out how to get Rust to match the enum, is there a way to do this with match instead of if statements?

+    if let AnnouncableActivities::UndoVote(_) = activity {
+      warn!("zebratrace310 SKIP UndoVote");
+    } else if let AnnouncableActivities::Vote(_) = activity {
+      warn!("zebratrace310A SKIP Vote");
+    } else {
+      warn!("zebratrace311 send");
+      AnnounceActivity::send(activity.clone().try_into()?, community, context).await?;
+    };

Code seems to work great, blocks UndoVote/Vote but does the send on comment reply.

more "correct" way would be this:

match activity {
    AnnouncableActivities::UndoVote(_) => warn!("zebratrace310 SKIP UndoVote"),
    AnnouncableActivities::Vote(_) => warn!("zebratrace310A SKIP Vote"),
    _ => {
        warn!("zebratrace311 send");
        AnnounceActivity::send(activity.clone().try_into()?, community, context).await?;
    },
}

here it is in the rust book: https://doc.rust-lang.org/stable/book/ch06-02-match.html

ool. I found the syntax for multiple hits, so I was looking for:

match activity {
    AnnouncableActivities::UndoVote(_)  |
    AnnouncableActivities::Vote(_) => {
        warn!("zebratrace310 SKIP federating Vote/UndoVote");
    },
    _ => {
        warn!("zebratrace311 send");
        AnnounceActivity::send(activity.clone().try_into()?, community, context).await?;
    },
}

Thank you.

15 comments