Very long young gc pause (ParNew with CMS)

[Florian Binder]

Hi everybody,

I am using CMS (with ParNew) gc and have very long (> 6 seconds) young 
gc pauses.
As you can see in the log below the old-gen-heap consists of one large 
block, the new Size has 256m, it uses 13 worker threads and it has to 
copy 27505761 words (~210mb) directly from eden to old gen.
I have seen that this problem occurs only after about one week of 
uptime. Even thought we make a full (compacting) gc every night.
Since real-time > user-time I assume it might be a synchronization 
problem. Can this be true?

Do you have any Ideas how I can speed up this gcs?

Please let me know, if you need more informations.

Thank you,
Flo


##### java -version #####
java version "1.6.0_29"
Java(TM) SE Runtime Environment (build 1.6.0_29-b11)
Java HotSpot(TM) 64-Bit Server VM (build 20.4-b02, mixed mode)

##### The startup parameters: #####
-Xms28G -Xmx28G
-XX:+UseConcMarkSweepGC \
-XX:CMSMaxAbortablePrecleanTime=10000 \
-XX:SurvivorRatio=8 \
-XX:TargetSurvivorRatio=90 \
-XX:MaxTenuringThreshold=31 \
-XX:CMSInitiatingOccupancyFraction=80 \
-XX:NewSize=256M \

-verbose:gc \
-XX:+PrintFlagsFinal \
-XX:PrintFLSStatistics=1 \
-XX:+PrintGCDetails \
-XX:+PrintGCDateStamps \
-XX:-TraceClassUnloading \
-XX:+PrintGCApplicationConcurrentTime \
-XX:+PrintGCApplicationStoppedTime \
-XX:+PrintTenuringDistribution \
-XX:+CMSClassUnloadingEnabled \
-Dsun.rmi.dgc.server.gcInterval=9223372036854775807 \
-Dsun.rmi.dgc.client.gcInterval=9223372036854775807 \

-Djava.awt.headless=true

##### From the out-file (as of +PrintFlagsFinal): #####
ParallelGCThreads                         = 13

##### The gc.log-excerpt: #####
Application time: 20,0617700 seconds
2011-12-22T12:02:03.289+0100: [GC Before GC:
Statistics for BinaryTreeDictionary:
------------------------------------
Total Free Space: 1183290963
Max   Chunk Size: 1183290963
Number of Blocks: 1
Av.  Block  Size: 1183290963
Tree      Height: 1
Before GC:
Statistics for BinaryTreeDictionary:
------------------------------------
Total Free Space: 0
Max   Chunk Size: 0
Number of Blocks: 0
Tree      Height: 0
[ParNew
Desired survivor size 25480392 bytes, new threshold 1 (max 31)
- age   1:   28260160 bytes,   28260160 total
: 249216K->27648K(249216K), 6,1808130 secs] 
20061765K->20056210K(29332480K)After GC:
Statistics for BinaryTreeDictionary:
------------------------------------
Total Free Space: 1155785202
Max   Chunk Size: 1155785202
Number of Blocks: 1
Av.  Block  Size: 1155785202
Tree      Height: 1
After GC:
Statistics for BinaryTreeDictionary:
------------------------------------
Total Free Space: 0
Max   Chunk Size: 0
Number of Blocks: 0
Tree      Height: 0
, 6,1809440 secs] [Times: user=3,08 sys=0,51, real=6,18 secs]
Total time for which application threads were stopped: 6,1818730 seconds
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