Ruby on Rails out of the box gets a lot of bad rep for being slow and non-performant. Has anyone replaced MRI with JRuby or TruffleRuby to mitigate that? Were there any significant "gotchas" with integrating it?
The biggest dealbreaker was that (like most Rails apps) we had a ton of gems, some of which had native extensions. JRuby doesn't support C native extensions.
In the end, it was way easier (and a much less risky change) to spin up our own Java REST APIs in front of those JARs, and let our MRI Rails app integrate with them by talking to those REST endpoints.
Just for fun, I also tried using dRuby so an MRI Rails app and a small JRuby (non-Rails) process could communicate idiomatically. It was cool, but I'm pretty sure dRuby was eventually deprecated.
Does this story answer your question about performance? Not really, but if I wanted to dive deeper (which I do at some point!) I think TruffleRuby is a real option.