Major GC happening before suggested CMSInitiatingOccupancyFraction

prashant Kumar prashant.kumar at agnity.com
Mon Jan 12 08:59:21 UTC 2009


Hi There,

 

I am using below mentioned options for my server. The issue is that I have
set CMSInitiatingOccupancyFraction=65 but major GC is happening at a lower
value of heap used (approximately 50%) though it should happen at around
65%. Due to this CPU utilization increases to a very high value. I am not
able to find out the reason of major GC.

 

P.S. Logs are attached with the mail.

 

Options:

 

-Xdebug -Xnoagent -debug
-Xrunjdwp:transport=dt_socket,address=8000,server=y,suspend=n,stdalloc=y
-Xmx2048m -Xms2048m -XX:NewSize=96m -XX:MaxNewSize=96m -XX:+UseTLAB
-XX:+UseParNewGC -XX:+UseConcMarkSweepGC
-XX:CMSInitiatingOccupancyFraction=65 -XX:+DisableExplicitGC -verbose:gc
-XX:+PrintGCTimeStamps -XX:+PrintGCDetails -XX:+PrintTenuringDistribution
-XX:PrintCMSStatistics=1 -XX:PrintFLSStatistics=1 -XX:+PrintHeapAtGC
-XX:PermSize=64m -XX:MaxPermSize=64m

 

 

This is the output of the logs:

 

Desired survivor size 32768 bytes, new threshold 0 (max 0)

: 98176K->0K(98240K), 0.1769591 secs] 1093934K->1003680K(2097088K)Statistics
for BinaryTreeDictionary:

------------------------------------

Total Free Space: 252988590

Max   Chunk Size: 252988590

Number of Blocks: 1

Av.  Block  Size: 252988590

Tree      Height: 1

Statistics for BinaryTreeDictionary:

------------------------------------

Total Free Space: 0

Max   Chunk Size: 0

Number of Blocks: 0

Tree      Height: 0

 Heap after GC invocations=447:

Heap

 par new generation   total 98240K, used 0K [0x75800000, 0x7b800000,
0x7b800000)

  eden space 98176K,   0% used [0x75800000, 0x75800000, 0x7b7e0000)

  from space 64K,   0% used [0x7b7f0000, 0x7b7f0000, 0x7b800000)

  to   space 64K,   0% used [0x7b7e0000, 0x7b7e0000, 0x7b7f0000)

 concurrent mark-sweep generation total 1998848K, used 1003680K [0x7b800000,
0xf5800000, 0xf5800000)

 concurrent-mark-sweep perm gen total 65536K, used 16879K [0xf5800000,
0xf9800000, 0xf9800000)

} , 0.1779375 secs]

After GC:

After GC:

8784.678: [GC [1 CMS-initial-mark: 1003680K(1998848K)] 1003698K(2097088K),
0.0052064 secs]

8784.684: [CMS-concurrent-mark-start]

8787.045: [CMS-concurrent-mark: 2.361/2.361 secs]

 (CMS-concurrent-mark yielded 0 times)

8787.046: [CMS-concurrent-preclean-start]

 (cardTable: 2726 cards, re-scanned 2726 cards, 1 iterations)

8788.370: [CMS-concurrent-preclean: 1.320/1.324 secs]

 (CMS-concurrent-preclean yielded 0 times)

8788.371: [GC8788.371: [Rescan (parallel) , 0.3424891 secs]8788.714: [weak
refs processing, 0.0569442 secs] [1 CMS-remark: 1003680K(1998848K)]
1055351K(2097088K), 0.4066270 secs]

8788.799: [CMS-concurrent-sweep-start]

8791.891: [GC  {Heap before GC invocations=447:

Heap

 par new generation   total 98240K, used 98176K [0x75800000, 0x7b800000,
0x7b800000)

  eden space 98176K, 100% used [0x75800000, 0x7b7e0000, 0x7b7e0000)

  from space 64K,   0% used [0x7b7f0000, 0x7b7f0000, 0x7b800000)

  to   space 64K,   0% used [0x7b7e0000, 0x7b7e0000, 0x7b7f0000)

 concurrent mark-sweep generation total 1998848K, used 742483K [0x7b800000,
0xf5800000, 0xf5800000)

 concurrent-mark-sweep perm gen total 65536K, used 16879K [0xf5800000,
0xf9800000, 0xf9800000)

Statistics for BinaryTreeDictionary:

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