NewRatio: to twiddle or not to twiddle

Tom Rodriguez Thomas.Rodriguez at Sun.COM
Tue Sep 2 12:52:23 PDT 2008

Which collector are you using?  -client defaults to the serial  
collector which isn't adaptive at all.  -server will use the parallel  
collector which tries to resize the new generation to improve  
collector performance.  If you are running with -client try adding -XX: 
+UseParallelGC.  I often see much better performance with -client just  
from this change.


On Sep 2, 2008, at 11:50 AM, Charles Oliver Nutter wrote:

> I've ben playing with JRuby on various benchmarks recently and found  
> that several object-intensive scripts run better if I set  
> NewRatio=1. Ruby, even more than Java, tends to generate lots and  
> lots of objects, especially considering that there's no unboxed  
> primitive numeric types (and no fixnums on the JVM...ahem ahem). So  
> my general theory is that:
> 1. A NewRatio of 1 allows all those extra transient objects to get  
> collected more quickly.
> 2. Too small a "new" generation causes transient objects to get  
> shoved into older generations, potentially snowballing and forcing  
> more comprehensive GC runs as time goes on.
> I'm curious whether this theory sounds reasonable, whether there's a  
> better way I can adapt hotspot to the memory demands of a dynamic  
> language like Ruby, and what other implications there are in setting  
> NewRatio to 1.
> Thoughts?
> (And please let me know if there's a better list to post this sort  
> of question to)
> - Charlie

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