JRuby is fast for a Ruby implementation, but it's still far, far slower than Scala or Java itself.

http://shootout.alioth.debian.org/u32/benchmark.php?test=all...

A lot of the pain a site like Twitter will have comes from GC (they wrote their own Ruby GC), and JRuby has a much better garbage collector over MRI and probably better than Twitter's.

It seems like something like Twitter would benefit lots from a good generational GC. Any more info on the one they wrote and how it differs from the built-in one? I'd love to learn more.

I do get that a dynamic language like Ruby will always be slower than a language like Java, which has primitives and where many things, including static method calls, are solved at compile time.

But citing the Alioth.Debian benchmarks? Really?

Dude, take a look at the source-code of those benchmarks sometimes -- they are completely useless ;)

Dude, "completely useless" is just "completely useless" name calling.

Say what you think is wrong with the source-code of particular programs.

If you want a fast dynamic language, take a look at Lua. It's surprisingly fast, especially LuaJIT, and pretty straight forward (almost boring really). The main downside is that there isn't the breadth of community around it.

Lua's threading is just as broken as Python or Ruby. Maybe even more so.

They're as useful as the code is well written for each language.

You think the Ruby code could be faster, and thus the comparison is skewed? Go ahead and help everyone understand by improving it.

They show the right order-of-magnitude differences. Taking them more seriously than that is a mistake.

That JRuby :: Scala URL shows an interquartile range from 6x to 31x so which order-of-magnitude were you going to pick? ;-)

it's still slower than ruby 1.9 is it not? I was under the impression the current perf hierarchy was 1.9.2p290 w / gc cleanup patch (ree inspired) > jruby > 1.8.7 (ree) > all the other rubies?

I recall reading an interview with Evan Weaver that the problem with moving to JRuby was in client libraries they were using, not JRuby itself.

That is indeed the issue if you want to convert an existing rails app to JRuby. But if you're just starting out, it's a different story: you'll end up much more JVM-focused since the best option is generally to use the java equivalent instead of a ruby gem, but there are options.

I've been using rails for almost 7 years now (holy crap) and run a medium-sized site on it. It works just fine, but if I were starting from scratch today, I would still use Rails, but I'd run it on JRuby.

Agreed. There are certainly some people who can't use the JVM for some reason (client libraries being a common one), but I think most people would be best served by using JRuby. There's a lot of innovation going on there, and platforms like Torquebox[1] have some compelling benefits.

1. http://torquebox.org/