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Comment by bt848 | Hacker News Reader

I don't know if raft "rocked" paxos's boat or not. It's a social phenomenon where Stanford people and their associates evangelize raft not because it is superior but just because it came from Stanford. People think raft is easier to implement but from my studies of available implementations the truth is it's actually just more likely that someone will Dunning-Krueger their way into believing they can implement it. There are a large number of defective raft implementations in the wild. There are almost no paxos implementations, correct or otherwise, making it harder to reason about its popularity and ergonomics. One thing is for sure: if you think you do not quite understand paxos then it is quite likely that you also do not understand raft, even though raft makes you feel like you might.

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The Raft paper has a full section on understandability, and comes with a TLA+ spec.

I am baffled that a serious effort at producing papers that are understandable and implementable is dismissed as a “social phenomenon”. Deliberately obscure papers are bad, sloppy science, not a clever signaling mechanism.

As pointed out elsewhere in the conversation and indeed in revised editions of the Paxos paper, it does not even break new ground and is equivalent to the earlier view management protocol.

Raft also has a frequently-linked, simple visual explanation[1]. If that's at all accurate to what Raft is, that would certainly make Raft easier to understand than Paxos, although that's a function of the learning materials available, not anything inherently more understandable about the algorithm itself.

I feel that I understand Raft and not Paxos, although currently that's simply because I haven't yet tried to understand Paxos. But the reason I am still interested in Paxos is that looking at Raft, it still seems like Raft has a bottleneck at the leader. Essentially, it looks like what makes this distributed consensus look simple is that only leader elections are actually distributed: the rest of the algorithm isn't distributed at all. When I get around to reading about Paxos I'm hoping it will be different.

[1] https://raft.github.io/

I find that the core of Paxos (the Synod protocol) is very easy to understand - it is literally just two exchanges of messages! The tricks that you need to add to go from the Synod protocol and get an actual production implementation of the replicated log are another matter, the original paper only hints about some of them. There is e.g. the Paxos Made Live paper (link: https://www.cs.utexas.edu/~lorenzo/corsi/cs380d/papers/paper...) that has more on this topic.

BTW Paxos also has a leader - this is what makes these protocols efficient. They need only the linear number of messages instead of the quadratic "everybody talks to everybody" design.

>BTW Paxos also has a leader - this is what makes these protocols efficient.

That's the funny part of Paxos. Paxos is specifically sold as a multi-proposer protocol. The most subtle and hard to understand part of the protocol is the clever 2 phase proposal election with value inheritance. But it's all pointless because in order to make the system work you need a single coordinator you elect using timeouts or reliable message protocols.

> BTW Paxos also has a leader - this is what makes these protocols efficient. They need only the linear number of messages instead of the quadratic "everybody talks to everybody" design.

Okay, but again, this means that the leader is the bottleneck. In that case, I'd want the leader to be on beefier hardware than the other machines, and to not serve up any read requests, so all of its resources are devoted to leading. In order to accommodate this, you'd want to elect leaders from a pool of leaders which have the beefier hardware. And at that point, since you're only talking to the leaders when you write, rather than talk through to the leaders through the extra latency of the followers, just write to the leaders directly. And then at that point this looks suspiciously like the leaders are a sharded database and the followers are caches. Am I missing something?

Word on the street is if you really really try to understand Paxos you will find that its much more nuanced and complex than raft. Many have tried, but failed.

>There are almost no paxos implementations, correct or otherwise, making it harder to reason about its popularity and ergonomics.

If I was cynical, I might guess that the purpose of Paxos these days is to generate expenses and technical failures for Google's competitors.

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