option combinations

Victor Cheung VictorC at ganz.com
Sun Dec 14 08:36:29 PST 2008


I see.  Is this the order of precedence?:

-Xmn  >  (-XX:NewSize  -XX:MaxNewSize)  >  -XX:NewRatio

victor

________________________________
From: Michael Finocchiaro [michael.finocchiaro at gmail.com]
Sent: Sunday, December 14, 2008 10:56 AM
To: Victor Cheung
Subject: Re: option combinations

Personally, I'd go with Xmn as dynamic resizing of New is not generally a good idea unless you are using Java7 and G3 and since I previously mentioned that NewRatio is overridden by almost every other parameter and is HIGHLY untrustworthy.
Cheers,
Fino

Michael Finocchiaro
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On Sun, Dec 14, 2008 at 4:51 PM, Victor Cheung <VictorC at ganz.com<mailto:VictorC at ganz.com>> wrote:
Regarding sizing the young generation, I seem to remember reading that the order the options are defined matters, and that the last one defined wins...  so if you had "-Xmn=256m -XX:NewRatio=3 -XX:NewSize=128m" the winner is 128m.  Can anyone confirm this?  (if this is not true, then what is the overriding order of these options to set the young generation size?)

incidentally, are there more ways to set the young generation size?

victor

________________________________________
From: Michael Finocchiaro [michael.finocchiaro at gmail.com<mailto:michael.finocchiaro at gmail.com>]
Sent: Sunday, December 14, 2008 2:48 AM
To: Y Srinivas Ramakrishna
Cc: Victor Cheung; hotspot-gc-use at openjdk.java.net<mailto:hotspot-gc-use at openjdk.java.net>
Subject: Re: option combinations

I have found that NewRatio is overridden by almost any other flag and
that it is recommended to use Xmn instead.
Also beware that CMS will set SurvivorRatio=1024 but that you can
specify SurvivorRatio explicitly to override this.
All ParNewGC/CMS flags are unique to the low-pause collector (same
goes for ParallelGC/ParallelOldGC for the throughout collector) except
as Ramki said ParallelGCThreads.
I think that Java6 gave us control for the CMSThreads or am I mistaken?
Cheers,
Fino

Sent from Fino's iPhone 3G

On 14 déc. 08, at 08:40, Y Srinivas Ramakrishna
<Y.S.Ramakrishna at Sun.COM> wrote:

>
>> i can't seem to find a comprehensive listing or matrix of which
>> options are valid with each other.
>>
>> does anyone know of such information?
>
> Unfortunately, no such documentation exists, as far as i know.
>
> If you have questions about specific combinations, we can try and
> answer them.
>
> We can, of course, also think about how one might go about
> documenting this combinatorial morass. Any suggestions/examples?
> (The general problem of transcription of the combinatorial
> possibilities is of course intractable, but the problem may well
> be tractable for HotSpot options by means of partitioning into
> orthogonal
> subsets/"partitions".)
>
> -- ramki
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