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rgevaerd
Joined: 22 Jun 2009
Posts: 2
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 Posted: Mon Jun 22, 2009 1:08 pm Post subject: GC Telemetry with Concurrent Mark and Sweep garbage collector |
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At end of http://profiler.netbeans.org/docs/help/5.5/concept_gc.html it says that the monitor does not work when your target JVM uses the Concurrent Mark and Sweep garbage collector.
I searched but could not find anything about it for newer NetBeans versions.
Can the information about GC relative time be trusted when the target VM uses the Concurrent Mark and Sweep garbage collector, in the current (6.5/6.7) NetBeans? |
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Tomas Hurka
Posted via mailing list.
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| Posted: Wed Jul 01, 2009 12:47 pm Post subject: GC Telemetry with Concurrent Mark and Sweep garbage collector |
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Hi,
On 22 Jun 2009, at 15:08, rgevaerd wrote:
| Quote: | At end of http://profiler.netbeans.org/docs/help/5.5/concept_gc.html
it says that the monitor does not work when your target JVM uses the
Concurrent Mark and Sweep garbage collector.
I searched but could not find anything about it for newer NetBeans
versions.
Can the information about GC relative time be trusted when the
target VM uses the Concurrent Mark and Sweep garbage collector, in
the current (6.5/6.7) NetBeans?
|
There is no change against NB 5.5. GC relative time is relative wall-
clock time spend in GC. For Concurrent Mark and Sweep garbage
collector we know when GC starts and ends, but we don't know how much
CPU time was spend by GC itself. So you may see that GC relative time
is high, but your application can run since actual CPU time taken by
GC is low.
Bye,
--
Tomas Hurka <mailto:address-removed>
NetBeans Profiler http://profiler.netbeans.org
VisualVM http://visualvm.dev.java.net
Software Engineer, Developer Platforms Group
Sun Microsystems, Praha Czech Republic
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rgevaerd
Joined: 22 Jun 2009
Posts: 2
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| Posted: Wed Jul 01, 2009 1:24 pm Post subject: Re: GC Telemetry with Concurrent Mark and Sweep garbage collector |
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| Tomas Hurka wrote: | There is no change against NB 5.5. GC relative time is relative wall-
clock time spend in GC. For Concurrent Mark and Sweep garbage
collector we know when GC starts and ends, but we don't know how much
CPU time was spend by GC itself. So you may see that GC relative time
is high, but your application can run since actual CPU time taken by
GC is low.
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Actually, the GC relative time shown for CMS was quite small for me, in a simple test done. While ParallelGC averaged around 3% and had peaks of 20% during major collections, CMS averaged around 1% and showed no peaks during major collections (besides a single initial peak of 50/60% that both had). |
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