Recently on this blog, I wrote about in-memory filesystems in Rust, and concluded that I wasn’t able to detect a difference between any form of in-memory filesystem and using a regular SSD on macOS. I also asked anyone who found a counterexample to please let me know. Last week, David Barsky of ERSC sent me an extremely compelling counter-example, and I spent several days running benchmarks to understand it better. The top level summary is that the test suite for the jj VCS exhibits an abso...
