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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