CMS Full GC

[Srinivas Ramakrishna]

Is it possible that you are GC'ing here to expand perm gen. Check if
permgen footprint changed between the two JVM releases (when running yr
application).
Now, CMS should quietly expand perm gen without doing a stop-world GC, but
there was a temporary regression in that functionality before it was fixed
again.
I can't however recall the JVM versions where the regression was introduced
and then fixed. But all of this is handwaving on my part.
If you run 6u22 and 6u29 both with -XX:+PrintHeapAtGC, you might have more
visibility into why the GC is kicking in. A longer log would allow
the community to perhaps provide suggestions as well.

Which reminds me that there is a bug in the printing of GC cause (as
printed by jstat) which needs to be fixed. HotSpot/GC folk, have you
noticed that we never
see a "perm gen allocation" as the GC cause even when that's really the
reason for a full gc? (not that that should happen here where CMS is being
used.)

-- ramki

On Tue, Apr 17, 2012 at 8:08 AM, Shivkumar Chelwa <schelwa at tibco.com> wrote:

>  Hi,****
>
> ** **
>
> Till date I was using JRE 6u22 with following garbage collection
> parameters and the CMS cycle use to kick-in appropriately (when heap
> reaches 75%)****
>
> ** **
>
> ** **
>
> -server -d64 -Xms2048m -Xmx2048m -javaagent: my-instrumentation.jar
> -XX:MaxPermSize=256m -XX:+UseParNewGC -XX:+UseConcMarkSweepGC
> -XX:+DisableExplicitGC -XX:CMSInitiatingOccupancyFraction=75
> -XX:+UseCMSInitiatingOccupancyOnly -verbose:gc -Xloggc:LB01.log
> -XX:+PrintGCTimeStamps -XX:+PrintGCDetails
> -Djava.library=/usr/java/jre/lib/sparcv9/server/libjvm.so -Xmx8192M
> -Xms8192M -Xss256K****
>
> ** **
>
> But I switched to JRE 6u29 and see the *CMS Full GC* happening randomly.
> Can you please help me undercover this mystery. Here is one of the log
> message from gc log file.****
>
> ** **
>
> 13475.239: [*Full GC* 13475.239: [CMS: 4321575K->3717474K(7898752K), *54.0602376
> secs*] 4412277K->3717474K(8339648K), [CMS Perm : 73791K->73339K(74048K)],
> 54.0615557 secs] [Times: user=53.97 sy****
>
> s=0.12, real=54.06 secs]****
>
> ** **
>
> ** **
>
> Kindly help.****
>
> ** **
>
> ** **
>
> Regards,****
>
> Shiv****
>
> ** **
>
> ** **
>
> ** **
>
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