jmap命令

http://blog.csdn.net/fenglibing/article/details/6411953

 

jmap 的用途是為了展示java進程的內存映射信息，或者堆內存詳情

常用的參數如下：

histo

jmap -histo pid 展示class的內存情況

展示的信息為編號，實例數，字節，類名

 

 

heap

jmap -heap pid 展示pid的整體堆信息

    jmap -heap 2464  
    JVM version is 16.3-b01  
      
    using thread-local object allocation.  
    Parallel GC with 13 thread(s)  
      
    Heap Configuration:  
       MinHeapFreeRatio = 40  
       MaxHeapFreeRatio = 70  
       MaxHeapSize      = 8436842496 (8046.0MB)  
       NewSize          = 5439488 (5.1875MB)  
       MaxNewSize       = 17592186044415 MB  
       OldSize          = 5439488 (5.1875MB)  
       NewRatio         = 2  
       SurvivorRatio    = 8  
       PermSize         = 21757952 (20.75MB)  
       MaxPermSize      = 88080384 (84.0MB)  
      
    Heap Usage:  
    PS Young Generation  
    Eden Space:  
       capacity = 87883776 (83.8125MB)  
       used     = 31053080 (29.614524841308594MB)  
       free     = 56830696 (54.197975158691406MB)  
       35.33425782706469% used  
    From Space:  
       capacity = 13828096 (13.1875MB)  
       used     = 196608 (0.1875MB)  
       free     = 13631488 (13.0MB)  
       1.4218009478672986% used  
    To Space:  
       capacity = 16384000 (15.625MB)  
       used     = 0 (0.0MB)  
       free     = 16384000 (15.625MB)  
       0.0% used  
    PS Old Generation  
       capacity = 156172288 (148.9375MB)  
       used     = 27098208 (25.842864990234375MB)  
       free     = 129074080 (123.09463500976562MB)  
       17.35148299805917% used  
    PS Perm Generation  
       capacity = 88080384 (84.0MB)  
       used     = 50847592 (48.492042541503906MB)  
       free     = 37232792 (35.507957458496094MB)  
       57.728622073218936% used  

 

 

說明如下

Parallel GC with 13 thread(s)   #13個gc線程  
  
Heap Configuration:#堆內存初始化配置  
   MinHeapFreeRatio = 40  #-XX:MinHeapFreeRatio設置JVM堆最小空閑比率  
   MaxHeapFreeRatio = 70  #-XX:MaxHeapFreeRatio設置JVM堆最大空閑比率  
   MaxHeapSize      = 8436842496 (8046.0MB)#-XX:MaxHeapSize=設置JVM堆的最大大小  
   NewSize          = 5439488 (5.1875MB) #-XX:NewSize=設置JVM堆的‘新生代’的默認大小  
   MaxNewSize       = 17592186044415 MB  #-XX:MaxNewSize=設置JVM堆的‘新生代’的最大大小  
   OldSize          = 5439488 (5.1875MB) #-XX:OldSize=設置JVM堆的‘老生代’的大小  
   NewRatio         = 2 #-XX:NewRatio=:‘新生代’和‘老生代’的大小比率  
   SurvivorRatio    = 8 #-XX:SurvivorRatio=設置年輕代中Eden區與Survivor區的大小比值  
   PermSize         = 21757952 (20.75MB) #-XX:PermSize=<value>:設置JVM堆的‘永生代’的初始大小  
   MaxPermSize      = 88080384 (84.0MB) #-XX:MaxPermSize=<value>:設置JVM堆的‘永生代’的最大大小  
  
Heap Usage:  
PS Young Generation  
Eden Space:#Eden區內存分布  
   capacity = 87883776 (83.8125MB)  
   used     = 31053080 (29.614524841308594MB)  
   free     = 56830696 (54.197975158691406MB)  
   35.33425782706469% used  
From Space:#其中一個Survivor區的內存分布  
   capacity = 13828096 (13.1875MB)  
   used     = 196608 (0.1875MB)  
   free     = 13631488 (13.0MB)  
   1.4218009478672986% used  
To Space:#另一個Survivor區的內存分布  
   capacity = 16384000 (15.625MB)  
   used     = 0 (0.0MB)  
   free     = 16384000 (15.625MB)  
   0.0% used  
PS Old Generation#當前的Old區內存分布  
   capacity = 156172288 (148.9375MB)  
   used     = 27098208 (25.842864990234375MB)  
   free     = 129074080 (123.09463500976562MB)  
   17.35148299805917% used  
PS Perm Generation#當前的 “永生代” 內存分布  
   capacity = 88080384 (84.0MB)  
   used     = 50847592 (48.492042541503906MB)  
   free     = 37232792 (35.507957458496094MB)  
   57.728622073218936% used 

 

dump

導出的文件可以供分析用，比如jhat或者mat，以便查找內存溢出原因