Facebook 为啥使用 Mercurial 代替 Git？
在 Facebook 官方博客上找到一篇介绍这个话题的文章，主要是 Mercurial 易扩展，更重要的是开发者社区友好（针对 Facebook 的现状帮忙定位问题，并在新功能开发时候考虑 Facebook 的特殊情况）。

Instead, we chose to improve Mercurial. Mercurial is a distributed source control system similar to Git, with many equivalent features. Importantly, it’s written mostly in clean, modular Python (with some native code for hot paths), making it deeply extensible. Just as importantly, the Mercurial developer community is actively helping us address our scaling problems by reviewing our patches and keeping our scale in mind when designing new features.

https://engineering.fb.com/core-data/scaling-mercurial-at-facebook/