The performance intensive parts of GitLab are written in Go, for example https://gitlab.com/gitlab-org/gitlab-workhorse/

We're working on moving the git commands to https://gitlab.com/gitlab-org/gitaly/ this will help to improve cloning speeds.

BTW The people at Booking have a lot of expertise in scaling Git. I'm sure there will be a lot Gitly there we can learn from.

I misremembered.

By the way, which mature web language is fast these days? Go is not quite there in terms of maturity, and everything else is "slow" (maybe the Microsoft stack is fast?), but I'm a web developer by trade and none of my views have been CPU-bound in... ever.

Common Lisp :)

Go is certainly there.

Go's ecosystem is as large as Python's/Ruby's/Node's? I very much doubt that.