Here's my implementation in Go, which runs in under 5 seconds. It doesn't use anything too obscure, only the built-in maps and no external libraries. It's also the fastest solution I've tested on my M3 Pro Mac. Eager to see what beats it!
On most Linux distributions and when the file is mmap'd, if you run it a second time the data will still be in RAM and not have to be read from disk. This gets the runtime down to 1.1s for this AMD 2950x (https://github.com/gunnarmorling/1brc/discussions/46#discuss...).
https://github.com/gunnarmorling/1brc#results
The fastest is currently at 12 seconds (not on M3 Pro though).