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

[Jon Masamitsu]

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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