Gossip For Lakitu

by Jens Alfke ⟿ August 16, 2009

Last year I wrote a series of blog posts about a peer-to-peer system called Cloudy that I was developing. I was going up the stack, from messaging to identity, but didn’t finish documenting all the layers I’d built. I mostly stopped working on Cloudy after I went back to gainful employment, but I keep thinking about this stuff.


I’ve since heard about another unrelated project nicknamed Cloudy; and the whole term “cloud” has gotten so debased in the past year that it now stands for outsourcing to giant hidden server farms, which is the antithesis of what I stand for. So I’ve decided to use the name Lakitu instead. Nintendo fans will recognize Lakitu as a bit character in the Mario games — he’s a goggled turtle who rides a little one-seater cloud. This makes him an appropriate mascot for P2P technologies, I think.

[I’m sure Nintendo has a trademark on the character, but they don’t appear to have copyrighted the word “Lakitu”. He’s not even known by that name in Japan, where he’s called “ジュゲム” or “Jugem”. I have been unable to find out what “Lakitu” means or why they decided to use it in the English translation. I could also note threateningly that I have some intellectual-property issues of my own with Nintendo’s depiction of Lakitu’s smiling cloud, which is clearly infringing on my son’s comic-strip character Cloudy. So let’s call it a draw, Iwata-san?]

My last Cloudy post was about verifying people’s identities, and the next one was going to be about gossip. I’ve become unhappy about the rather kludgy way I designed gossip in Cloudy, so yesterday I started designing a new protocol for it, which I’m going to write about.


A gossip protocol is a means of broadcasting information in a distributed system. Pairs of computers periodically connect and swap new bits of information with each other; the result is that the information gets dispersed through the whole network (provided it’s a connected graph.) The tricky part is avoiding infinite loops and combinatorial explosions, and optimizing the way pairs of computers swap messages so it scales well.

I started defining a protocol, based on stuff I’ve been thinking about for a while. I don’t think it’s as advanced as what’s reported in research papers, but I’m hoping it will work well enough when used in a socially-driven network — one where the connections between machines are driven by the social connections between their users. Social networks have short horizons, so any particular participant only “sees” a constrained number of near-neighbors even though the entire network may be huge.

I’m making this protocol agnostic as to the type of messaging being used. BLIP will work well, but it ought to be possible to use Jabber or even email; anything that can send messages between two participants. It’s also agnostic as to message content, beyond a few simple assumptions that a message has an author, a timestamp, and some arbitrary “topic” tags.

For example, it ought to work fine at distributing tweet-like micro-blog posts.

Right now I have the protocol written down as an outline in Notebook. I’ll flatten it out, expand it and post it here in a day or two.