JVM内存使用观测

1. 如果是本机或者网络环境好，单进程, 使用jconsole.

2.如果是服务器监控进程JVM内部堆内存情况，使用jstat,,非常便于观察垃圾回收以及堆内存的情况。

3. JVM进程当前的实例占用情况， 已启动进程的参数情况，使用jmap:

 如jmap -histo  28217   显示当前JVM进程实例和内存

 jmap -dump:format=b,file=test.bin 4939   显示dump文件，使用MAT分析即可.

jmap -heap pid 显示JVM参数配置

using thread-local object allocation.
Parallel GC with 13 thread(s)


Heap Configuration:
   MinHeapFreeRatio = 40
   MaxHeapFreeRatio = 70
   MaxHeapSize      = 3221225472 (3072.0MB)
   NewSize          = 1073741824 (1024.0MB)
   MaxNewSize       = 1073741824 (1024.0MB)
   OldSize          = 4194304 (4.0MB)
   NewRatio         = 2
   SurvivorRatio    = 8
   PermSize         = 16777216 (16.0MB)
   MaxPermSize      = 67108864 (64.0MB)
   G1HeapRegionSize = 0 (0.0MB)


Heap Usage:
PS Young Generation
Eden Space:
   capacity = 357957632 (341.375MB)
   used     = 353057456 (336.7018280029297MB)
   free     = 4900176 (4.6731719970703125MB)
   98.63107374673883% used
From Space:
   capacity = 357892096 (341.3125MB)
   used     = 0 (0.0MB)
   free     = 357892096 (341.3125MB)
   0.0% used
To Space:
   capacity = 357892096 (341.3125MB)
   used     = 0 (0.0MB)
   free     = 357892096 (341.3125MB)
   0.0% used
PS Old Generation
   capacity = 2147483648 (2048.0MB)
   used     = 2147481696 (2047.9981384277344MB)
   free     = 1952 (0.001861572265625MB)
   99.99990910291672% used
PS Perm Generation
   capacity = 16777216 (16.0MB)
   used     = 12090240 (11.5301513671875MB)
   free     = 4686976 (4.4698486328125MB)
   72.06344604492188% used


7709 interned Strings occupying 619624 bytes.

4.简单的内存使用测试用sar就行了。