1.4.2 PrintFLSStatistics Output

[Neeraj Jain]

We are using Java 1.4.2_17 (64-bit mode) to run long running server
application on solaris using following java options

-server -d64 -XX:+HandlePromotionFailure
-XX:CMSInitiatingOccupancyFraction=70 -XX:NewSize=256m -XX:MaxNewSize=2
56m -XX:SurvivorRatio=10 -XX:+UseConcMarkSweepGC -XX:+UseParNewGC
-XX:+PrintTenuringDistribution -XX:PrintCMSStatistics=1 -XX:+PrintGCDetails
-XX:+Pri
ntGCTimeStamps -XX:PrintFLSStatistics=1 -XX:+PrintHeapAtGC
-XX:+PrintClassHistogram -XX:PermSize=96m -XX:MaxPermSize=96m
-XX:MaxTenuringThreshold=5 -X
ms6g -Xmx6g -Xss256k

In order to isolate a fragmentation issue, we started using
-XX:PrintFLSStatistics option to see if the fragmentation is really taking
place. However, the output looks quite confusing. I have following specific
queries around this (please refer to the GC logs given below):

1. As per GC stats, around 5 GB of memory is taken by the application so
there should be ~0.75 GB free in tenured generation but BinaryTreeDictionary
statistics show only around 38 MB of memory in Free List Trees? Where have
the rest of 700 MB gone?

2. Going by these stats, the total free space is only 349438 words (~2.8 MB)
but still minor collections succeed (before eventually getting promotion
failed error). Where does the free space to provide Young Generation
Guarantee (~240 MB) come from?

3. Why there are two sets of BinaryTreeDictionary stats?

Any help will be greatly appreciated. Thanks in advance.

Neeraj

=======================================JVM GC
Logs====================================================

40330.741: [ParNewBefore GC:
Before GC:

Desired survivor size 11173888 bytes, new threshold 2 (max 5)
- age   1:    7549224 bytes,    7549224 total
- age   2:    5868416 bytes,   13417640 total
: 231488K->13203K(240320K), 0.4537259 secs]
5235545K->5023066K(6269632K)Statistics for BinaryTreeDictionary:
------------------------------------
Total Free Space: 349438
Max   Chunk Size: 349438
Number of Blocks: 1
Av.  Block  Size: 349438
Tree      Height: 1
Statistics for BinaryTreeDictionary:
------------------------------------
Total Free Space: 4440679
Max   Chunk Size: 4440679
Number of Blocks: 1
Av.  Block  Size: 4440679
Tree      Height: 1
 Heap after GC invocations=2396:
Heap
 par new generation   total 240320K, used 13203K [0xfffffffdefc00000,
0xfffffffdffc00000, 0xfffffffdffc00000)
  eden space 218496K,   0% used [0xfffffffdefc00000, 0xfffffffdefc00000,
0xfffffffdfd160000)
  from space 21824K,  60% used [0xfffffffdfd160000, 0xfffffffdfde44d50,
0xfffffffdfe6b0000)
  to   space 21824K,   0% used [0xfffffffdfe6b0000, 0xfffffffdfe6b0000,
0xfffffffdffc00000)
 concurrent mark-sweep generation total 6029312K, used 5009862K
[0xfffffffdffc00000, 0xffffffff6fc00000, 0xffffffff6fc00000)
 concurrent-mark-sweep perm gen total 98304K, used 63210K
[0xffffffff6fc00000, 0xffffffff75c00000, 0xffffffff75c00000)
} , 0.4557118 secs]
After GC:
After GC:
40344.958: [GC  {Heap before GC invocations=2396:
Heap
 par new generation   total 240320K, used 231699K [0xfffffffdefc00000,
0xfffffffdffc00000, 0xfffffffdffc00000)
  eden space 218496K, 100% used [0xfffffffdefc00000, 0xfffffffdfd160000,
0xfffffffdfd160000)
  from space 21824K,  60% used [0xfffffffdfd160000, 0xfffffffdfde44d50,
0xfffffffdfe6b0000)
  to   space 21824K,   0% used [0xfffffffdfe6b0000, 0xfffffffdfe6b0000,
0xfffffffdffc00000)
 concurrent mark-sweep generation total 6029312K, used 5008129K
[0xfffffffdffc00000, 0xffffffff6fc00000, 0xffffffff6fc00000)
 concurrent-mark-sweep perm gen total 98304K, used 63210K
[0xffffffff6fc00000, 0xffffffff75c00000, 0xffffffff75c00000)
Statistics for BinaryTreeDictionary:
------------------------------------
Total Free Space: 353702
Max   Chunk Size: 349438
Number of Blocks: 9
Av.  Block  Size: 39300
Tree      Height: 5
Statistics for BinaryTreeDictionary:
------------------------------------
Total Free Space: 4440679
Max   Chunk Size: 4440679
Number of Blocks: 1
Av.  Block  Size: 4440679
Tree      Height: 1
40344.960: [ParNewBefore GC:
Before GC:
 (promotion failed)
Desired survivor size 11173888 bytes, new threshold 2 (max 5)
- age   1:    7604792 bytes,    7604792 total
- age   2:    5978704 bytes,   13583496 total
: 231699K->231699K(240320K), 1.2985705 secs]40346.259: [CMS40358.345:
[CMS-concurrent-sweep: 25.860/27.699 secs]
 (CMS-concurrent-sweep yielded 2 times)
 (concurrent mode failure)[Unloading class
sun.reflect.GeneratedSerializationConstructorAccessor93]
[Unloading class sun.reflect.GeneratedSerializationConstructorAccessor30]
[Unloading class sun.reflect.GeneratedSerializationConstructorAccessor55]
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