FWIW, Mergify's Merge Queue supports this as long as you run it without batching or parallel checks. We expose a config option for semi-linear history while still keeping CI green.
That's super interesting, thanks for sharing the Yelp/PayPal lineage. You're right: there's probably a lot of prior art in internal release engineering systems that never got much written up publicly.
The angle we took in the blog post focused on what was widely documented and accessible to the community (open-source tools like Bors, Homu, Bulldozer, Zuul, etc.), because those left a public footprint that other teams could adopt or build on.
It's a great reminder that many companies were solving the "keep main green" problem in parallel (some with pretty sophisticated tooling), even if it didn't make it into OSS or blog posts at the time.
That's a good point. To clarify, Gerrit itself didn't actually do merge queuing or CI gating. Its model was stacked commits: every change was rebased on top of the current tip of main before landing. That ensured a linear history but didn't solve the "Is the whole pipeline still green when we merge this?" problem.
That's why the OpenStack community built Zuul on top of Gerrit: it added a real gating system that could speculatively test multiple commits in a queue and only merge them if CI passed together. In other words, Zuul was Gerrit's version of a merge queue.
Question: You list Uber (my employer) as a user in your homepage, but searching internally, the only search result for mergify is a mergify.yml in some random debian module for lua, so it doesn't seem like we actually use it for anything (and we built an in-house solution for the repos w/ serious commit traffic). I'm curious how you determine who your corporate users are?
Comment: we ended up building a merge queue in house because frankly build/test pipelines can look very different,(e.g. at one point we had jenkins pipelines and buildkite pipelines, some using bazel, some not, talking to phabricator instead of github, etc). At the end of day plugging in a merge queue technology requires a bunch of work integrating with a myriad of things anyways. Since the engineering effort is relatively high regardless, doing it in house lets us experiment with more aggressive optimization heuristics than just waiting on a 3rd party.
We know Uber has some great internal tooling (there's even a paper published on their merge queue: https://eng.uber.com/research/keeping-master-green-at-scale/). We had various Uber engineers using Mergify on open source repositories those last years. I didn't check recently if that was still the case, I'll make sure our lis is not too much outdated.
I definitely agree with your view on how pipelines can be different. I think none of our customers has something that is exactly the same. However, many of them don't have the workforce to build in house or even to optimize as far as you would do in a (very) large company.
