runtime JVM options

Rainer Jung rainer.jung at kippdata.de
Fri Dec 12 00:59:27 PST 2008


Am 12.12.2008 05:32, schrieb Peter B. Kessler:
> Victor Cheung wrote:
>> Total time for which application threads were stopped: 0.0000723
>> seconds
>
> This is from -XX:+PrintGCApplicationStoppedTime see [1] line 480 for
> details.
>
>> Application time: 0.0000304 seconds
>
> This is from -XX:+PrintGCApplicationConcurrentTime see [1] line 429
> for details.  This is somewhat confusing, because those two flags
> actually track when the virtual machine comes to a "safepoint".
> Since there isn't any GC activity, I surmise that the VM is coming to
> a safepoint for some other reason.  For example, the VM has to come
> to a safepoint to install code it compiles at runtime.

I asked the same question 2 months ago, because with Java 6 you can see 
especially in early applucation phases a lot of very short additional 
stop messages. Tony Printezis pointed out to me, that this could also 
happen due to the use of biased locking:

 > They could be biased locking revocation safepoints.
 > Try running with -XX:-UseBiasedLocking to see if they occur.
 > Biased locking is an important and effective optimization in
 > most cases and the extra safepoints that it causes are
 > generally benign and nothing to worry about.

I verified, that this was the reason in our situation. As already 
mentioned, those are extremely short and even when multiplied with the 
number of occurances nothing to worry about.

Regards,

Rainer
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