I didn’t delve very deep into it, but the program was written in Go. At this point in the lifecycle of the program we had optimized it quite a bit, removing all the inefficiencies that we could. It was now spending around two thirds of its cpu cycles on garbage collection. It had this ridiculously large heap that was still growing, but hardly any of it was actually garbage.

I rewrote a slice of the program in Rust with quite promising results, but by that time there wasn’t really any demand left. You see, one of the many uses of Reposurgeon <http://www.catb.org/esr/reposurgeon/> is to convert SVN repositories into Git repositories. These performance results were taken while reposurgeon was running on a dump of the GCC source code repository. At the time this was the single largest open source SVN repository left in the world with 287k commits. Now that it’s been converted to a Git repository it’s unlikely that future Reposurgeon users will have the same problem.

Also, someone pointed out that MG-LRU <https://docs.kernel.org/admin-guide/mm/multigen_lru.html> might help by increasing the block size of the reads and writes. It was introduced a year or more after I took these screenshots, so I can’t easily verify that.