JVM性能调试之jmap

http://snv.iteye.com/blog/1826402

JVM性能调试之jmap

博客分类：  Java

 

jmap 的用途是为了展示java进程的内存映射信息，或者堆内存详情

常用的参数如下：

histo

jmap -histo pid 展示class的内存情况

展示的信息为编号，实例数，字节，类名

例如：

 jmap -histo:live 2540

  num     #instances         #bytes  class name
 ----------------------------------------------
    1:         20981         908120  [C
    2:         21015         504360  java.lang.String
    4:          9999         159984  org.learn.util.User
    5:           312          59216  [Ljava.lang.Object;

 

heap

 

jmap -heap pid 展示pid的整体堆信息

如：

 

 $ jmap -heap 29030
 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

 对应的说明如下：

 

 

 Parallel GC with 13 thread(s)   #13个gc线程

 Heap Configuration:#堆内存初始化配置
    MinHeapFreeRatio = 40  #-XX:MinHeapFreeRatio设置JVM堆最小空闲比率
    MaxHeapFreeRatio = 70  #-XX:MaxHeapFreeRatio设置JVM堆最大空闲比率
    MaxHeapSize      = 8436842496 (8046.0MB)#-XX:MaxHeapSize=设置JVM堆的最大大小
    NewSize          = 5439488 (5.1875MB) #-XX:NewSize=设置JVM堆的‘新生代’的默认大小
    MaxNewSize       = 17592186044415 MB  #-XX:MaxNewSize=设置JVM堆的‘新生代’的最大大小
    OldSize          = 5439488 (5.1875MB) #-XX:OldSize=设置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=设置年轻代中Eden区与Survivor区的大小比值
    PermSize         = 21757952 (20.75MB) #-XX:PermSize=:设置JVM堆的‘永生代’的初始大小
    MaxPermSize      = 88080384 (84.0MB) #-XX:MaxPermSize=:设置JVM堆的‘永生代’的最大大小

 Heap Usage:
 PS Young Generation
 Eden Space:#Eden区内存分布
    capacity = 87883776 (83.8125MB)
    used     = 31053080 (29.614524841308594MB)
    free     = 56830696 (54.197975158691406MB)
    35.33425782706469% used
 From Space:#其中一个Survivor区的内存分布
    capacity = 13828096 (13.1875MB)
    used     = 196608 (0.1875MB)
    free     = 13631488 (13.0MB)
    1.4218009478672986% used
 To Space:#另一个Survivor区的内存分布
    capacity = 16384000 (15.625MB)
    used     = 0 (0.0MB)
    free     = 16384000 (15.625MB)
    0.0% used
 PS Old Generation#当前的Old区内存分布
    capacity = 156172288 (148.9375MB)
    used     = 27098208 (25.842864990234375MB)
    free     = 129074080 (123.09463500976562MB)
    17.35148299805917% used
 PS Perm Generation#当前的 “永生代” 内存分布
    capacity = 88080384 (84.0MB)
    used     = 50847592 (48.492042541503906MB)
    free     = 37232792 (35.507957458496094MB)
    57.728622073218936% used

dump

 

jmap -dump:  pid 把pid的整体堆信息输出

dump-options：

live

format=b

file=

导出的文件可以供分析用，比如jhat或者mat，以便查找内存溢出原因

例如：

 jmap -dump:live,format=b,file=tomcat.bin 29030