You are thinking of dl.google.com. It was a Go program that replaced a very old single-threaded C++ server (using the ancient SelectServer C++ core, deprecated at that time). The thing you have to realize about Google infrastructure is it does not require vertical scalability of its service backends. It is very typical to write a program and deploy it with 100 replicas having one CPU each on 100 different machines. A variety of load balancers (all written in C++, naturally) papers over the complexity. Nobody at Google expects a Go program to occupy an entire machine because Borg packs hundreds of services onto a single machine. The question is for _you_ do _you_ have Borg or another workload coordinator that allows you to do this? Or do you have "the database machine" and "the server" where you expect individual processes to scale up to many cores?

BTW the reason dl.google.com rewrite was faster was not because it was in Go, it was because the C++ server was serving off its local disk and the rewrite was serving off a cluster file system with ~infinite I/O capabilities. Apples and oranges.