maybe I'm a weirdo, but I care a lot more about memory consumption than processing performance. Starting up irb with jruby-head and java 7u2 uses around 80MB. 80MB for vanilla irb!
MRI uses around 8MB
Edit: I get down voted for saying that I care about memory consumption? My use case may not be everyones, but it's a legitimate issue is it not?
JRuby largely uses more memory because we have a "real" garbage collector. The JVM, unlike MRI, allocates much more memory than the app needs. That gives it freedom to delay GC runs and push old objects into rarely-GCed sections of memory. It does also mean JRuby uses more memory on startup.
JRuby also has the JVM's subsystems booted and considerably more complex caching and optimization logic. This does increase the base size of a JRuby runtime.
It's possible to get JRuby to start in under 30MB if you explicitly force the JVM to use less memory with -J-Xmx30M or lower. But is it that big a deal? Let the JVM breathe, and your code runs better as a result.
First, I'd like to say that I use JRuby a lot, and you guys have done an amazing job on it. I complain because I like JRuby, and wish I could use it more :)
I did set the Xmx and it still uses around 80MB. I'm not sure what in the world the JVM is doing there, but the permgen is another 20MB or so and then other native stuff, thread overhead, etc.
Is memory cheap? Yes and no. At work we have a rails site with two REST api backends both ruby. I also love RubyMine. Now here's my problem, I can't run all of those on the JVM on my macbook air. 4 gigs is not enough if I also have a browser open!
This is not a problem at all if I switch the apps to MRI and switch my editor to a non JVM based editor. I think the JVM people need to recognize this problem.
MRI uses around 8MB
Edit: I get down voted for saying that I care about memory consumption? My use case may not be everyones, but it's a legitimate issue is it not?