option combinations

Victor Cheung VictorC at ganz.com
Sun Dec 14 07:31:02 PST 2008

I thought CMS only worked on the old generation heap.  Why does it affect survivor space sizing that is only in the young generation?  In any case, is the SurvivorRatio=1024 true for Linux 64-bit?

How can i tell which options are specific to ParNewGC (vs those specific to ParallelGC/ParallelOldGC)?

Another general question:  where can one find a listing of all the default values?  (this is why at the very beginning i asked if there was a way to find out *all* the options being used by a running JVM -- *all* meaning both the options explicitly set by the user, and also those automatically set by the JVM at runtime.  The answer to this was no.  The tools (jconsole, visualvm, jinfo) that i've tried so far only tell you what you already know -- i.e. only list the option values that you yourself explicitly set!

please don't tell me the answer is to read the code...


From: Michael Finocchiaro [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
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?

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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