Trace object type in GC

[Krystal Mok]

Hi San,

Wow, that's nice.
Is there any plans to submit it to hotspot-gc-dev as a patch to OpenJDK?

- Kris

On Tue, Jun 12, 2012 at 12:06 PM, Sam Pullara <spullara at twitter.com> wrote:

> What we would really like to have is a GC option that prints the top-N
> class histogram only for those that are being migrated from the oldest
> tenure age into the old generation. I have a prototype of it and it works,
> but it would be great if it was in the main code line.
>
> Sam
>
> On Jun 11, 2012, at 8:34 PM, Krystal Mok wrote:
>
> Hi Nicolas,
>
> If you're interested in the objects collected on a type-granularity, then
> the following VM arguments gets close:
>
> manageable(bool, PrintClassHistogramBeforeFullGC, false,          \
>         "Print a class histogram before any major stop-world GC") \
>                                                                   \
> manageable(bool, PrintClassHistogramAfterFullGC, false,           \
>         "Print a class histogram after any major stop-world GC")  \
>
> What they do is basically the same as running jmap -histo before or after
> a full GC, printing the histogram of objects grouped by class. Comparing
> the numbers before and after a full GC will give you the idea of what's
> collected in that full GC.
>
> You can turn these flags on by specifying them in the VM command line
> arguments, e.g. -XX:+PrintClassHistogramBeforeFullGC
> Or you could change their values while the VM is running, e.g. jinfo
> -flag +PrintClassHistogramBeforeFullGC <pid>
>
> (There's no equivalent flag for minor GCs in HotSpot.)
>
> If you're looking for information on a object-granularity, then it's
> something HotSpot VM doesn't support. GC implementations seldom track such
> information.
>
> Hope it helps,
> - Kris
>
> On Mon, Jun 11, 2012 at 11:36 PM, RICHARD Nicolas <
> nicolas.richard at atos.net> wrote:
>
>>  Dear hotspot developper,
>> I currently develop applications in Java.
>>
>> I am looking for a way to trace objects freed by the Garbage Collector.
>> For the time being, I've only found options to get statistics about GC
>> (execution time, average amount of freed memory, etc) but no one about the
>> type of object handled by the GC.
>>
>> Is there any option that I could use or is it possible to develop a JVM
>> TI agent to get this information ?
>>
>> Best regards
>> Nicolas RICHARD
>>
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