Jepsen: Capela dda5892 | Hacker News Reader

Jepsen: Capela dda5892

jepsen.io

81 pointsaphyr14 comments

Aside from obvious Smalltalk influence, this also brings to mind Darklang (that switched to an open-source model recently [1]).

I wonder how this will pan out... very interesting to see new approaches being explored.

[1]: https://news.ycombinator.com/item?id=44290653

Darklang is pretty fascinating, and was brought to our attention when we started demo-ing Capela to some folks in the industry. I think where Darklang (and others like Skip [1]) falls short is that it is a new language. Capela instead leverages typed Python, an existing and pretty familiar language to most programmers (and LLMs).

[1]: https://skiplabs.io

Oh, I just realized I am guilty of the drive-by-free-association comment without actually saying anything about the subject of the post - sorry!

Very cool to see a team use Jepsen for super early pre-release testing of the system.

I wonder if you wish you had waited for the runtime to be a bit more stable, or you feel this was already well worth the effort, even with some of the identified failures being in "known incomplete" areas? (I could see either side of the argument - waiting longer might give you more valuable failures, but testing early gives you a chance to catch problems before they become baked into the foundation and become more difficult to fix...)

Another tool that feels like sci-fi to me any time I hear a mention of it, is Antithesis [1] - written by the people who built FoundationDB. Could be another interesting integration to investigate in the future to help bulletproof the language runtime?

[1]: https://antithesis.com

Author here--from discussions with Capela's team, I think this sort of early testing can be remarkably helpful, because it offers a test suite that Capela's team can check their work against as they move forward.

I would suggest against this kind of integration test when the data model or API are in constant flux, because then you have to re-write or even re-design the test as the API changes. Small changes--adding fields or features, changing HTTP paths or renaming fields--are generally easy to keep up with, but if there were, say, a redesign that removed core operations, or changed the fundamental semantics, it might require extensive changes to the test suite.

We thought a lot about this, and decided to not wait since we are a pretty small team and having more hands helping us to catch any problems early on would help us to make better technical decisions as we continue evolving the core platform. In addition to that, we gained a pretty robust CI step to keep us accountable around the guarantees that we want to provide. Reliably and consistently storing data is of utmost importance for us.

The plan is to engage with Jepsen again once we have a system that passes the current suite, expand the test surface even further, and continue iterating until we are satisfied with the results. There won't be a public release before that is true.

Working with Jepsen also sparked a couple other interesting ideas, like building a Python language fuzzer to ensure that many shapes of Python programs work as intended in Capela. That's something we would love to do in the future.

Re: Antithesis - absolutely. Kyle mentioned them to us and we think it will be a very interesting product for us to adopt to further ensure we're delivering a reliable product.

If it's partly a marketing move to get it jepsened before release, then it worked on me.

"Like Smalltalk and other image-based languages, Capela persists program state directly, and allows programs to be modified over time. Indeed, Capela feels somewhat like an object-oriented database with stored procedures."

This seems exciting.

Derek from Capela here. Marketing was not our primary purpose, but I guess it worked out as such ;)

The primary reason for us engaging early on with Jepsen is that we care a lot about correctness, consistency and reliability, and we wanted the best in this field to establish a baseline of tests that we must make sure our platform passes before we even put it the hands of anybody.

You should team up with Antithesis. https://antithesis.com/

Kyle connected us already - we definitely plan to leverage their product for extra layers of verification!

I was thinking of something deeper than just using their product.

Regardless, it's a good way to reach people that care about robust distributed systems or queers in tech or both.

Do you have a business model already? Are you aiming for something like GemStone/S?

Reading the first line I thought it was about https://github.com/eclipse-capella/capella, the Foss solution for Model-Based Systems Engineering. Confusing. But now there is also a Capela with a single ‘l’ -) Great writeup Kyle, thank you!

does Jepsen's test software auto-generate the cool diagrams (like 3.22) or do you have to do it yourself? do you prefer any software to do that?

It does indeed! This is a part of https://github.com/jepsen-io/elle, which infers totally-connected components of the transaction dependency graph. :-)

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