CASPaxos: Linearizable Databases Without Logs | Hacker News Reader

CASPaxos: Linearizable Databases Without Logs

reubenbond.github.io

49 pointsGordonS10 comments

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Shameless plug for my writeup of all the different paxos varieties:

https://vadosware.io/post/paxosmon-gotta-concensus-them-all

(lots of links to papers inside)

It's a fascinating field and there are a LOT of variations of Paxos worth investigating.

I recently added a ToC so that it's a little easier to navigate/jump around

Anyone have a link to the actual whitepaper? The one in the OP 404s.

Edit: it's https://arxiv.org/pdf/1802.07000.pdf

Fixed, thanks for pointing that out. I didn't realize this was posted here.

It seems like a riff on replication where you replicate values instead of operations in a traditional database.

Relevant Tweet by Denis Rystsov, author of "CASPaxos: Replicated State Machines without logs": https://twitter.com/rystsov/status/1118201415577419776

CASPaxos has nice latency and recovery times on node failures and partition re-joins. The author of the algorithm has a comparison with other popular consistent distributed databases https://github.com/rystsov/perseus

I particularly like novelty of using a function closures which makes it elegant and approachable.

I also found the idea of the hierarchical ballots from the article pretty interesting. ([config ballot, range ballot, file ballot, register ballot]). And I suppose in the spirit of the original paper, it would be a nested set of closures :-)

One thing that might not be obvious though, compared to other databases, is that reads essentially follow the same path as the writes and cost about the same, and even might result in spreading the update to other nodes that don't have the latest value.

> It is a slight modification of the original Paxos algorithm, which is very simple and typically used as a minimal building block for more complicated algorithms such as Multi-Paxos

Wasn't Raft invented as a teaching tool because Paxos was too hard to understand and implement correctly?

Personally, and I have heard many other people say this as well, I don't think Raft is any simpler than Paxos.

The problem with Paxos is that there is no one way to do things. There are a thousand different variants and techniques that are not all compatible with each other. So to actually implement Paxos essentially requires that you become an expert. The advantage of Paxos is that there are many potential optimizations at your fingertips, depending on your workload.

Unlike Paxos, Raft is much more prescriptive: do x, y, and z, and everything will be fine. And really, to a large extend, Raft can be viewed as a description of what many production Paxos implementations would look like.

> Paxos algorithm, which is very simple and typically used...

Madman, cult, or both?

I learned Paxos but not Raft. From memory, step one of Raft was to come to consensus on a leader. Isn't that in itself entirely what Paxos solves?

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