NewRatio: to twiddle or not to twiddle

Charles Oliver Nutter charles.nutter at
Tue Sep 2 14:11:42 PDT 2008

kirk wrote:
> Hi Charles,
> Peter, awesome explination. I use hpjmeter right now to do very gross 
> analysis on gc logs. It doesn't tolerate all the Sun non-standard 
> non-standard switches (-XX and as apposed to the standard non-standard 
> switches -X) ;-) I've also signed up with Tony to work in gchisto, a 
> tool that should be more tolerant to Sun gc logs (is there anyway we can 
> settle on a standard format???) though that tool is still very limited. 
> Eventually it should get rolled into visualvm but that is a future.

If not a standard format, at least a version-frozen format with a 
header, eh?

I'll have to look into hpjmeter. At the moment I think half our 
"problems" on JRuby come from lack of experience with the right tools to 
gain visibility into the JVM. Oh, and lack of resources; two guys does 
not a language implementation team make.

> What I'm finding is that techniques that focus more on evacuation seem 
> to work better than those that focus on collection compaction. This is 
> one of the reasons I'm very interested in seeing G1 released into the 
> wild. I believe that G1 will mix very well with dynamic languages 
> because it primary logic is on evacuation. With G1, I don't believe it 
> will matter if old fills up with transient objects that maybe should 
> have died in young. In fact I'd bet money that G1 will excel under these 
> conditions because old spaces will be evacuated based on who has the 
> lowest live ratios. The biggest draw back that I can see will be copying 
> costs. Even so, expect a win.

If it's true that G1 (what is G1?) wouldn't care about transient objects 
getting promoted, I'd be interested in that as well. Overall, though, I 
think the exercise of exploring memory usage patterns to reduce such 
promotions will be very important, since there's going to be a lot of 
users on less helpful JVM versions, hotspot or otherwise.

- Charlie

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