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Comment by j2kun | Hacker News Reader

I started using git as my daily driver at Google in 2018. I was forcibly kicked off it for mercurial in 2020. The deprecation plan for mercurial is 2026 IIUC. Maybe if you adopted mercurial early it's different.

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What was the reason for using Mercurial?

Why did Google decide to choose Mercurial? Based on what I read the main reason was that the mercurial dev team was willing to prioritize features needed for Google to add custom extensions to support its monorepo, and the git dev team wasn't going to reprioritize just for the sake of Google.

I think you’re confusing Google with Facebook.

j2kun seems to be a googler so I don't think so, but it's true that Facebook also went with Mercurial. I suspect it was for similar reasons.

Ahh. It sounded like a repeat of https://graphite.dev/blog/why-facebook-doesnt-use-git but maybe it did happen for both companies! They’d obviously be having similar issues. Thanks :)

I can second that the aforementioned reasons are true. The funny difference is that Google employs the primary git maintainer. Git has a lot of customers though so it rightfully is very conservative with development.

Yes, that's correct. Another reason was that Mercurial is easier to customize because it's written in Python so we could sometimes just replace whatever we needed without needing much changes from Mercurial itself.

Yet another reason is that the .git directory is considered a documented API and several other tools and libraries depend on it (e.g. JGit and libgit2). So any new features for Google would need to be made to those tools too if we wanted things built on them to work.

We also consider Mercurial to have better UX.

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