Question about -XX:+PrintTenuringDistribution and age not being printed.

[John O'Brien]

Thanks for the quick response today.

To finish up,using Parallel old with  UseAdaptivePolicy is true by
default and I  -XX:MaxTenuringThreshold=3  I expected an incompatible
parameter error.
I did not get it.  The logs  show the tenuring threshold adjusted
below and above the value of 5 e.g "new threshold 7 (max 5)."

Then I decided to switch of useAdaptiveSizePolicy and see if threshold
would be stuck at 5 but no threshold logs were printed.

My  question: Does   -XX:MaxTenuringThreshold=3 work with
ParallelScavenge? (Seems not).

Looks like my  override is to fix size the survivor spaces through use
of some other flags? This will also turn off adaptivesizepolicy as it
is not needed.

Regards,
John


On Fri, Apr 27, 2012 at 2:29 PM, Jon Masamitsu <jon.masamitsu at oracle.com> wrote:
> John,
>
>
> On 4/27/2012 2:03 PM, John O'Brien wrote:
>> Hi everyone,
>>
>> I understand that :
>>
>> 1) par-new has features that make it work with CMS.
>
> Yes.
>
>> 2) par-scavenge does not have these features and is incompatible with CMS.
> Yes.
>> 3) Otherwise they are the same core algorithm...both parallel stop the
>> world copying collectors.
>
> ParNew and Parallel Scavenge are two different implementations of
> parallel STW
> collectors.  They share some code but much is different.  ParallelScavenge
> support UseAdaptiveSizePolicy and ParNew does not (never finished).
> ParallelScavenge
> varies the tenuring threshold to keep the survivor spaces from
> overflowing and
> also varies the sizes of the survivor spaces relative to eden while ParNew
> has a fixed ratio between eden and the survivor sizes.  It's hard to
> keep track
> of the differences.
>
>> Why does PrintTenuringDistribution only print out the ages when ParNew
>> is enabled?
>> If they are the same algorithm then shouldn't they both print out age
>> ? par-scavenge does not print "ages" for me when
>> PrintTenuringDistribution is on.
>
> Not the same algorithm.
>
>> I use Parallel Old and Parallel Scavenge (ParNew can't be used with
>> Parallel Old).
>
> Correct.
>
> Jon
>
>> Ref: https://blogs.oracle.com/jonthecollector/entry/our_collectors
>>
>> I searched the mailing lists and did not see anything , read some
>> blogs and looked through some books.
>>
>>
>> Regards,
>> John
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