Free space calculation of heap

[Bond Chen]

Hi,
 
Our application have suffer a bad fragmentation issue at production env, I need switch on lots of parameter to analysis the gc, but I'm not fully understand the all of the output.
 
By adding parameter -XX:PrintFLSStatistics=2 , The BinaryTreeDictionary and  IndexedFreeLists of old gen and perm gen have been printed out
 
q1: the total free space + used space of old gen calculation from gc output is 128KB less than actual old gen capacity
 
q2: all counter of the BinaryTreeDictionary and  IndexedFreeLists of perm gen is zero, why?
 
q3: what's the meaning of " frag=0.0045", fragmentation ratio? and can someone provide the formula?
 
q4: which parameter enables the "output log2 of gc log"? how to interpret the output
 
/**output log1 of gc log*/
 
67.016: [ParNew
Desired survivor size 111411200 bytes, new threshold 2 (max 32)
- age   1:   42577240 bytes,   42577240 total
- age   2:   74417368 bytes,  116994608 total
: 1512523K->153985K(1523200K), 0.2866570 secs] 1649586K->351496K(6000128K)After GC:
Statistics for BinaryTreeDictionary:
------------------------------------
Total Free Space: 546527717
Max   Chunk Size: 546527717
Number of Blocks: 1
Av.  Block  Size: 546527717
Tree      Height: 1
Statistics for IndexedFreeLists:
--------------------------------
Total Free Space: 1221215
Max   Chunk Size: 256
Number of Blocks: 39302
Av.  Block  Size: 31
 free=547748932 frag=0.0045
After GC:
Statistics for BinaryTreeDictionary:
------------------------------------
Total Free Space: 0
Max   Chunk Size: 0
Number of Blocks: 0
Tree      Height: 0
Statistics for IndexedFreeLists:
--------------------------------
Total Free Space: 0
Max   Chunk Size: 0
Number of Blocks: 0
 free=0 frag=0.0000
, 0.2868167 secs] [Times: user=0.91 sys=0.13, real=0.29 secs] 
Heap after GC invocations=6 (full 1):
 par new generation   total 1523200K, used 153985K [0xfffffd7e5ec10000, 0xfffffd7ec9010000, 0xfffffd7ec9010000)
  eden space 1305600K,   0% used [0xfffffd7e5ec10000, 0xfffffd7e5ec10000, 0xfffffd7eae710000)
  from space 217600K,  70% used [0xfffffd7eae710000, 0xfffffd7eb7d70438, 0xfffffd7ebbb90000)
  to   space 217600K,   0% used [0xfffffd7ebbb90000, 0xfffffd7ebbb90000, 0xfffffd7ec9010000)
 concurrent mark-sweep generation total 4476928K, used 197511K [0xfffffd7ec9010000, 0xfffffd7fda410000, 0xfffffd7fda410000)
 concurrent-mark-sweep perm gen total 524288K, used 238680K [0xfffffd7fda410000, 0xfffffd7ffa410000, 0xfffffd7ffa410000)
}
 
 
/***/
 
/**output log2 of gc log**/
2012-05-31T15:23:18.293+0800: 9.731: [CMS-concurrent-sweep-start]
size[1] : demand: 0, old_rate: 0.000000, current_rate: 0.000000, new_rate: 0.000000, old_desired: 0, new_desired: 0
size[2] : demand: 0, old_rate: 0.000000, current_rate: 0.000000, new_rate: 0.000000, old_desired: 0, new_desired: 0
size[3] : demand: 0, old_rate: 0.000000, current_rate: 0.000000, new_rate: 0.000000, old_desired: 0, new_desired: 0
size[4] : demand: 0, old_rate: 0.000000, current_rate: 0.000000, new_rate: 0.000000, old_desired: 0, new_desired: 0
size[5] : demand: 0, old_rate: 0.000000, current_rate: 0.000000, new_rate: 0.000000, old_desired: 0, new_desired: 0
...............................
size[250] : demand: 0, old_rate: 0.000000, current_rate: 0.000000, new_rate: 0.000000, old_desired: 0, new_desired: 0
size[251] : demand: 0, old_rate: 0.000000, current_rate: 0.000000, new_rate: 0.000000, old_desired: 0, new_desired: 0
size[252] : demand: 0, old_rate: 0.000000, current_rate: 0.000000, new_rate: 0.000000, old_desired: 0, new_desired: 0
size[253] : demand: 0, old_rate: 0.000000, current_rate: 0.000000, new_rate: 0.000000, old_desired: 0, new_desired: 0
size[254] : demand: 0, old_rate: 0.000000, current_rate: 0.000000, new_rate: 0.000000, old_desired: 0, new_desired: 0
size[255] : demand: 0, old_rate: 0.000000, current_rate: 0.000000, new_rate: 0.000000, old_desired: 0, new_desired: 0
size[256] : demand: 0, old_rate: 0.000000, current_rate: 0.000000, new_rate: 0.000000, old_desired: 0, new_desired: 0
demand: 1, old_rate: 0.000000, current_rate: 0.103071, new_rate: 0.103071, old_desired: 0, new_desired: 0
 
***/
 
Many Thanks
Bond
 

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