From: Charles Oliver Nutter <charles.nutter@...>
Date: 2007-11-01T09:00:25+09:00
Subject: Re: JRuby perf questions answered

Roger Pack wrote:
> Roger Pack wrote:
>>> any questions?
>> Startup time and comparison with 1.9? :)
> 
> Also memory use comparison compared to normal C version.  Does the GC 
> throw as often, too?

In profiling most apps I've tried, even pretty brutal ones generating a 
lot of garbage, the GC cost is almost invisible. A tiny blip once in a 
while.

I don't have any really good concrete numbers on overall memory usage. 
Tom's done a comparison of a minimal/bare Rails app here:

http://www.bloglines.com/blog/ThomasEEnebo?id=38

The general story is that per JRuby on Rails instance (usually you have 
many in a single JVM), we use less memory than an equivalent Mongrel + 
Ruby + Rails process.

A quick check of "jirb" compared to "irb" gives me:

jirb: 27MB
irb: 2.8MB

This is on OS X, Java 6 preview version, so it's safe to say that any 
JRuby process will have an initial cost of about 25MB to start up the JVM.

We've also done a lot in 1.1 to reduce memory consumption, and there's 
more work coming up.

- Charlie