I don’t think Rails is anywhere close to light enough for the memory overhead of threads to be the important limiting factor. For an async server or something l

I don’t think Rails is anywhere close to light enough for the memory overhead of threads to be the important limiting factor. For an async server or something like project loom to pay off you need the request processing to be light and the time to be dominated by IO which can either be explicitly converted to async IO and callbacks or implicitly turned into async IO by your language’s standard library (as we are doing with Java and Loom). In my experience even with a JIT Rails is spending a lot of time in all the layers of request processing, so it has limited throughout even when the actual IO is trivial. No async framework can save you from processing overhead like that. Note: I work on TruffleRuby and Project Loom.