Growing GC Young Gen Times

Y. Srinivas Ramakrishna y.s.ramakrishna at
Wed May 12 23:38:51 UTC 2010

Try the jvm from hs18 (jdk 7) and let us know what you see.
Or wait for JDK 6u21 which (i think) is slated for sometime
next month. Or get an hs17 JVM with the fix 6631166 via
your Java support and give it a try.

Also add -XX:+UseLargePages -XX:+AlwaysPreTouch and if
you have enough cores try increasing yr ParallelGCThreads from
your current setting of 4 (what was the default you got?).

I have not looked at the log you sent, but can take a look
when i get some time; but no promises, as i am drowned in
other work at the moment.

-- ramki

On 05/12/10 15:19, Matt Fowles wrote:
> All~
> I have a large app that produces ~4g of garbage every 30 seconds and
> am trying to reduce the size of gc outliers.  About 99% of this data
> is garbage, but almost anything that survives one collection survives
> for an indeterminately long amount of time.  We are currently using
> the following VM and options:
> java version "1.6.0_20"
> Java(TM) SE Runtime Environment (build 1.6.0_20-b02)
> Java HotSpot(TM) 64-Bit Server VM (build 16.3-b01, mixed mode)
>                -verbose:gc
>                -XX:+PrintGCTimeStamps
>                -XX:+PrintGCDetails
>                -XX:+PrintGCTaskTimeStamps
>                -XX:+PrintTenuringDistribution
>                -XX:+PrintCommandLineFlags
>                -XX:+PrintReferenceGC
>                -Xms32g -Xmx32g -Xmn4g
>                -XX:+UseParNewGC
>                -XX:ParallelGCThreads=4
>                -XX:+UseConcMarkSweepGC
>                -XX:ParallelCMSThreads=4
>                -XX:CMSInitiatingOccupancyFraction=60
>                -XX:+UseCMSInitiatingOccupancyOnly
>                -XX:+CMSParallelRemarkEnabled
>                -XX:MaxGCPauseMillis=50
>                -Xloggc:gc.log
> As you can see from the GC log, we never actually reach the point
> where the CMS kicks in (after app startup).  But our young gens seem
> to take increasingly long to collect as time goes by.
> The steady state of the app is reached around 956.392 into the log
> with a collection that takes 0.106 seconds.  Thereafter the survivor
> space remains roughly constantly as filled and the amount promoted to
> old gen also remains constant, but the collection times increase to
> 2.855 seconds by the end of the 3.5 hour run.
> Has anyone seen this sort of behavior before?  Are there more switches
> that I should try running with?
> Obviously, I am working to profile the app and reduce the garbage load
> in parallel.  But if I still see this sort of problem, it is only a
> question of how long must the app run before I see unacceptable
> latency spikes.
> Matt
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