>At the same time, the larger tech companies (Meta and Google, specifically) ended up building off of hg and not git because (at the time, especially) git cannot scale up to their use cases.
Fun story: I don't really know what Microsoft's server-side infra looked like when they migrated the OS repo to git (which, contrary to the name, contains more than just stuff related to the Windows OS), but after a few years they started to hit some object scaling limitations where the easiest solution was to just freeze the "os" repo and roll everyone over to "os2".
“roll everyone over to os2”
The IBM crowd may feel vindicated at last.
So 30 odd years later, MS went from working on OS/2 to working on OS2?
I guess what's old is new again.
didn't msft write an ~entire new file system specifically to scale git to the windows code base?
I have fuzzy memories on reading about it.
They wrote something that allowed them to virtualize Git -- can't remember the name of that. But it basically hydrated files on-demand when accessed in the filesystem.
The problem was I think something to do with like the number of git objects that it was scaling to causing crazy server load or something. I don't remember the technical details, but definitely something involving the scale of git objects.
I thought Microsoft made a number of improvements to git to allow it work with all of their internal repos.
I have heard that the Google monorepo is called google3 but I don't know why. Maybe those things are common...
Probably a lot of Googlers don't know. It's ancient history, was called google3 even in 2006 when I first joined.
google1 = code written by Larry, Sergey and employee number 1 (Craig). A hacky pile of Python scripts, dumped fairly quickly.
google2 = the first properly engineered C++ codebase. Protobufs etc were in google2. But the build system was some jungle of custom Makefiles, or something like that. I never saw it directly.
google3 = the same code as google2 but with a new custom build system that used Python scripts to generate Makefiles. I suppose it required a new repository so they could port everything over in parallel with code being worked on in google2. P4 was apparently not that great at branches and google3 didn't use them. Later the same syntax for the build files was kept but turned into a new languages called Starlark and the Makefile generator went away in favor of Blaze, which directly interpreted them.
At least, that's the story I vaguely recall.
It's the third attempt of building the mono repo.
But not the 3rd mono repo on the same technology to avoid some scaling limit.
It's not that.
Thanks for explaining!