Answer by Schwern for How do you increase the starting memory and allocation rate of a Ruby process?

Running your benchmarks with Ruby 3.3.3 and JRuby 9.2.14.0 on macOS 14.5 on a 2018 Macbook Pro 2.7 Ghz i7, here's some simple observations by running top while the benchmarks run.

• JRuby uses a lot more memory. > 20+ GB vs < 10 GB.
• JRuby uses multiple cores, MRI Ruby does not.

I think all your benchmarking is that JRuby will use multiple cores to run the benchmark in parallel, but it's a memory hog. You can potentially recover this in MRI Ruby by using several Ractors, one or two for every core, to load data in parallel.