JVM中工具jmap的使用

jmap <Options> pid 

參數如下：  
-heap：打印jvm heap的情況  
-histo：打印jvm heap的直方圖。其輸出信息包括類名，對象數量，對象佔用大小。  
-histo：live ：只打印存活對象的情況  
-permstat：打印permanent generation heap情況  

[root@localhost ~]# jmap -heap 19600
Attaching to process ID 19600, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.221-b11

using thread-local object allocation.
Parallel GC with 2 thread(s)

Heap Configuration:
   MinHeapFreeRatio         = 0
   MaxHeapFreeRatio         = 100
   MaxHeapSize              = 515899392 (492.0MB)
   NewSize                  = 11010048 (10.5MB)
   MaxNewSize               = 171966464 (164.0MB)
   OldSize                  = 22544384 (21.5MB)
   NewRatio                 = 2
   SurvivorRatio            = 8
   MetaspaceSize            = 21807104 (20.796875MB)
   CompressedClassSpaceSize = 1073741824 (1024.0MB)
   MaxMetaspaceSize         = 17592186044415 MB
   G1HeapRegionSize         = 0 (0.0MB)

Heap Usage:
PS Young Generation
Eden Space:
   capacity = 35651584 (34.0MB)
   used     = 4152920 (3.9605331420898438MB)
   free     = 31498664 (30.039466857910156MB)
   11.64862688849954% used
From Space:
   capacity = 3670016 (3.5MB)
   used     = 1703936 (1.625MB)
   free     = 1966080 (1.875MB)
   46.42857142857143% used
To Space:
   capacity = 3670016 (3.5MB)
   used     = 0 (0.0MB)
   free     = 3670016 (3.5MB)
   0.0% used
PS Old Generation
   capacity = 22544384 (21.5MB)
   used     = 10071824 (9.605239868164062MB)
   free     = 12472560 (11.894760131835938MB)
   44.67553427053053% used

15456 interned Strings occupying 1376896 bytes.