java 1.7.0u4 GarbageCollectionNotificationInfo API

[Taras Tielkes]

Hi John,

Thanks for the feedback. The milliseconds/ticks issue indeed seems to be
bug 7087969. Will the upcoming 7u14 contain hs24, and the fix?

Regarding the "No GC" cause, I think
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8006954 might be the
underlying issue. If I understand correctly, it's now fixed for hs24 as
well, and will hopefully be part of 7u14.

I'll post any follow-up questions regarding the GC Notification API to the
serviceability-dev mailing list.

Kind regards,
-tt



On Fri, Feb 1, 2013 at 11:17 PM, John Cuthbertson <
john.cuthbertson at oracle.com> wrote:

>  Hi Taras,
>
> I'm going to cc the serviceability alias. I think they might be best
> suited to answer some of your questions. I believe they own the API and the
> GC provides the data.
>
> Answer 1: It should be milliseconds, but there was a bug (
> http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7087969) that is now
> fixed in hs24 and you could be running into that.
>
> Answer 2: This sounds like a bug. Do you have a test case you can share?
>
> Answer 3: I'll leave that to the serviceability guys.
>
> Regards,
>
> JohnC
>
>
> On 1/28/2013 1:11 PM, Taras Tielkes wrote:
>
>
>  Hi,
>
>  I'm playing around with the new(ish) GarbageCollectionNotificationInfo
> API. We're using ParNew+CMS in all our systems, and my first goal is a
> comparison between -XX:+PrintGCDetails -verbose:gc output and the actual
> data coming through the notification API. I'm using Java 1.7.0u6 for the
> experiments.
>
>  So far, I have a number of questions:
> 1) duration times
>
>  The javadoc for gcInfo.getDuration() describes the returned value as
> expressed in milliseconds. However, the values differ to the gc logs by
>  several orders of magnitude. How are they calculated?
>
>  On a 1-core Linux x64 VM, the values actually look like microseconds,
> but on a Win32 machines I still can't figure out any resemblance to gc log
> timings.
>
>  Apart from the unit, what should the value represent? Real time or user
> time?
>
>  2) CMS events with cause "No GC"
>
>  How exactly do the phases of CMS map to the notifications emitted for
> the CMS collector?
>
>  I sometimes get events with cause "No GC". Does this indicate a
> background CMS cycle being initiated by hitting the occupancy fraction
> threshold?
>
>  3) Eden/Survivor
>
>  It seems that the MemoryUsage API treats Eden and Survivor separately,
> i.e. survivor is not a subset of eden. This is different from the gc log
> presentation. Is my understanding correct?
>
>  In general, I think it would be useful to have a code sample for the GC
> notification API that generates output as close as possible to
> -XX:+PrintGCDetails -verbose:gc, as far as the data required to do so is
> available.
>
>  The API looks quite promising, it seems it could really benefit from a
> bit of documentation love :)
>
>  Thanks,
> -tt
>
>
>
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