As a fellow Facebook employee, FYI, Hacker News is not a great place to get tech support. For the benefit of everyone else on this thread, note that Facebook u

As a fellow Facebook employee, FYI, Hacker News is not a great place to get tech support. For the benefit of everyone else on this thread, note that Facebook uses https://github.com/facebookexperimental/eden https://github.com/facebookexperimental/eden. From the README: > Despite having originally evolved from Mercurial, EdenSCM is not a distributed source control system. i.e., this is not "stock" Mercurial. For example, the Eden server (Mononoke) is written in Rust and the complementary virtual filesystem is written in C++. This has very different performance characteristics than real Mercurial. EdenSCM works with both EdenFS (the custom filesystem) and a traditional filesystem. If you use EdenFS, pulls will be much cheaper because you only fetch what you use. If you use a traditional filesystem, EdenSCM supports the same "sparse checkouts" feature as stock Mercurial (https://firefox-source-docs.mozilla.org/build/buildsystem/sparse.html https://firefox-source-docs.mozilla.org/build/buildsystem/sp...), which can also be used to reduce the size of the slice of the monorepo you pull down. Last I checked, Perforce (and Google's "implementation" of Perforce, Piper) did not provide nearly the same level of support for stacked diffs as Eden. As both Google and Facebook have cultures of pre-commit code review, working with stacked diffs makes it much easier to make progress while waiting for approvals on earlier diffs. I believe there are relative advantages/disadvantages of Eden vs. Piper+CitC and that both projects aspire to have the best of each in the limit.