Comment by steventhedev

Comment by steventhedev 2 days ago

I'm gonna disagree with you there. The difference was with stat patterns, and the person at Facebook who ran the tests had something wrong with the disk setup that was causing it to run slowly. They ignored multiple responses that reproduced very different results.

Nail in the coffin on this was a benchmark GitHub ran two years ago that got the results that FB should have: git status within seconds.

Facebook didn't use mercurial because of big O, they used it because of hubris and a bad disk config.

sangnoir a day ago

> Facebook didn't use mercurial because of big O, they used it because of hubris and a bad disk config.

Half-remembering a blog post I read - the git maintainers also wouldn't give Facebook the time of day on code changes to accommodate FBs requirements. Mercurial was more amenable. This also disproves the "Facebook has a fork of evertyhing, because the attempted to upstream the changes they wanted)

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deadmutex 2 days ago

This sounds plausible, but would love a source

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steventhedev a day ago

I should probably just write it up into a post, but the git mailing list at the time is the source (I remember reading it from the side a few months after convincing our VP R&D to switch from svn to git). We were chuckling around the same time that FB had to reallocate the stack on Galaxy S2 phones because they were somehow unaware of proguard or unable to have it work properly with their codegen.
Anyways:
1. Github benchmark: https://github.blog/engineering/infrastructure/improve-git-m...
2. The original email thread: https://public-inbox.org/git/CB04005C.2C669%25joshua.redston...
3. There's another email thread that gets linked everywhere - but in light of the prior thread, the numbers don't track: https://public-inbox.org/git/CB5074CF.3AD7A%25joshua.redston...
I recall there being a message from someone either at AirBnB or Uber who mentioned that they have a similar monorepo but without the slow git status, but can't seem to find it now - it's likely on one of the other mailing list archives but didn't make it to this one.
Point being that painting this as "the community was hostile" or "git is too slow for FB" is just disingenuous. The FB engineer barely communicated with the git team (at least publicly) and when there was communication, it was pushing a single benchmark that was deeply flawed, and then ignoring feedback on how to both improve the performance of slow blame, commit by repacking checkpoint packfiles (a one-off effort) and also ignoring feedback that the benchmark numbers didn't make sense in absolute terms.

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