jmap命令详解

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JVM调优命令-jmap

 

jmap
JVM Memory Map命令用于生成heap dump文件，如果不使用这个命令，还可以使用-XX:+HeapDumpOnOutOfMemoryError参数来让虚拟机出现OOM的时候自动生成dump文件。 jmap不仅能生成dump文件，还可以查询finalize执行队列、Java堆和永久代的详细信息，如当前使用率、当前使用的是哪种收集器等。【内存分析】
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[[email protected] jdk1.7.0_79]# jmap --help
Usage:
    jmap [option] <pid>
        (to connect to running process)
    jmap [option] <executable <core>
        (to connect to a core file)
    jmap [option] [[email protected]]<remote server IP or hostname>
        (to connect to remote debug server)
 
where <option> is one of:
    <none>               to print same info as Solaris pmap
    -heap                to print java heap summary
    -histo[:live]        to print histogram of java object heap; if the "live"
                         suboption is specified, only count live objects
    -permstat            to print permanent generation statistics
    -finalizerinfo       to print information on objects awaiting finalization
    -dump:<dump-options> to dump java heap in hprof binary format
                         dump-options:
                           live         dump only live objects; if not specified,
                                        all objects in the heap are dumped.
                           format=b     binary format
                           file=<file>  dump heap to <file>
                         Example: jmap -dump:live,format=b,file=heap.bin <pid>
    -F                   force. Use with -dump:<dump-options> <pid> or -histo
                         to force a heap dump or histogram when <pid> does not
                         respond. The "live" suboption is not supported
                         in this mode.
    -h | -help           to print this help message
    -J<flag>             to pass <flag> directly to the runtime system

命令格式

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jmap [ option ] pid
jmap [ option ] executable core
jmap [ option ] [server-id@]remote-hostname-or-IP
 

参数

option：选项参数，不可同时使用多个选项参数

pid：java进程id，命令ps -ef | grep java获取

executable：产生核心dump的java可执行文件

core：需要打印配置信息的核心文件

remote-hostname-or-ip：远程调试的主机名或ip

server-id：可选的唯一id，如果相同的远程主机上运行了多台调试服务器，用此选项参数标识服务器

 

options参数

heap : 显示Java堆详细信息
histo : 显示堆中对象的统计信息
permstat :Java堆内存的永久保存区域的类加载器的统计信息
finalizerinfo : 显示在F-Queue队列等待Finalizer线程执行finalizer方法的对象
dump : 生成堆转储快照
F : 当-dump没有响应时，强制生成dump快照

 

示例

 

-dump

dump堆到文件,format指定输出格式，live指明是活着的对象,file指定文件名

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[[email protected] jdk1.7.0_79]# jmap -dump:live,format=b,file=dump.hprof 24971
Dumping heap to /usr/local/java/jdk1.7.0_79/dump.hprof ...
Heap dump file created

-heap

打印heap的概要信息，GC使用的算法，heap的配置及使用情况，可以用此来判断内存目前的使用情况以及垃圾回收情况

 

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[[email protected] jdk1.7.0_79]# jmap -heap 24971
Attaching to process ID 24971, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 24.79-b02
 
using thread-local object allocation.
Parallel GC with 4 thread(s)
 
Heap Configuration:
   MinHeapFreeRatio = 0
   MaxHeapFreeRatio = 100
   MaxHeapSize      = 4146069504 (3954.0MB)
   NewSize          = 1310720 (1.25MB)
   MaxNewSize       = 17592186044415 MB
   OldSize          = 5439488 (5.1875MB)
   NewRatio         = 2
   SurvivorRatio    = 8
   PermSize         = 21757952 (20.75MB)
   MaxPermSize      = 85983232 (82.0MB)
   G1HeapRegionSize = 0 (0.0MB)
 
Heap Usage:
PS Young Generation
Eden Space:
   capacity = 517996544 (494.0MB)
   used     = 151567520 (144.54605102539062MB)
   free     = 366429024 (349.4539489746094MB)
   29.26033421566612% used
From Space:
   capacity = 41943040 (40.0MB)
   used     = 0 (0.0MB)
   free     = 41943040 (40.0MB)
   0.0% used
To Space:
   capacity = 40370176 (38.5MB)
   used     = 0 (0.0MB)
   free     = 40370176 (38.5MB)
   0.0% used
PS Old Generation
   capacity = 115343360 (110.0MB)
   used     = 32927184 (31.401809692382812MB)
   free     = 82416176 (78.59819030761719MB)
   28.54709972034801% used
PS Perm Generation
   capacity = 85983232 (82.0MB)
   used     = 54701200 (52.16712951660156MB)
   free     = 31282032 (29.832870483398438MB)
   63.6184506300019% used
 
20822 interned Strings occupying 2441752 bytes.

-finalizerinfo

打印等待回收的对象信息，

 

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[[email protected] jdk1.7.0_79]# jmap -finalizerinfo 24971
Attaching to process ID 24971, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 24.79-b02
Number of objects pending for finalization: 0

Number of objects pending for finalization: 0 说明当前F-QUEUE队列中并没有等待Fializer线程执行final

izer方法的对象。

 

-histo

打印堆的对象统计，包括对象数、内存大小等等。jmap -histo:live 这个命令执行，JVM会先触发gc，然后再统计信息

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[[email protected] jdk1.7.0_79]# jmap -histo:live 24971 | more
 
 num     #instances         #bytes  class name
----------------------------------------------
   1:        100134       14622728  <constMethodKlass>
   2:        100134       12830128  <methodKlass>
   3:         88438       12708392  [C
   4:          8271       10163584  <constantPoolKlass>
   5:         27806        9115784  [B
   6:          8271        6225312  <instanceKlassKlass>
   7:          6830        5632192  <constantPoolCacheKlass>
   8:         86717        2081208  java.lang.String
   9:          2264        1311720  <methodDataKlass>
  10:         10880         870400  java.lang.reflect.Method
  11:          8987         869888  java.lang.Class
  12:         13330         747264  [[I
  13:         11808         733872  [S
  14:         20110         643520  java.util.concurrent.ConcurrentHashMap$HashEntry
  15:         18574         594368  java.util.HashMap$Entry
  16:          3668         504592  [Ljava.util.HashMap$Entry;
  17:         30698         491168  java.lang.Integer
  18:          2247         486864  [I
  19:          7486         479104  java.net.URL
  20:          8032         453616  [Ljava.lang.Object;
  21:         10259         410360  java.util.LinkedHashMap$Entry
  22:           699         380256  <objArrayKlassKlass>
  23:          5782         277536  org.apache.catalina.loader.ResourceEntry
  24:          8327         266464  java.lang.ref.WeakReference
  25:          2374         207928  [Ljava.util.concurrent.ConcurrentHashMap$HashEntry;
  26:          3440         192640  java.util.LinkedHashMap
  27:          4779         191160  java.lang.ref.SoftReference
  28:          3576         171648  java.util.HashMap
  29:         10080         161280  java.lang.Object

jmap -histo:live 24971 | grep com.yuhuo 查询类名包含com.yuhuo的信息

jmap -histo:live 24971 | grep com.yuhuo > histo.txt 保存信息到histo.txt文件

附 - jmap输出中class name非自定义类的说明：

BaseType CharacterTypeInterpretation
B byte signed byte
C char Unicode character
D double double-precision floating-point value
F float single-precision floating-point value
I int integer
J long long integer
L; reference an instance of class
S short signed short
Z boolean true or false
[ reference one array dimension，[I表示int[]

-permstat

打印Java堆内存的永久区的类加载器的智能统计信息。对于每个类加载器而言，它的名称、活跃度、地址、父类加载器、它所加载的类的数量和大小都会被打印。此外，包含的字符串数量和大小也会被打印。

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[[email protected] jdk1.7.0_79]# jmap -permstat 24971
Attaching to process ID 24971, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 24.79-b02
finding class loader instances ..done.
computing per loader stat ..done.
please wait.. computing liveness....................................................liveness analysis may be inaccurate ...
class_loader    classes bytes   parent_loader   alive?  type
 
<bootstrap>   3034    18149440      null      live    <internal>
0x000000070a88fbb8  1   3048      null      dead    sun/reflect/DelegatingClassLoader@0x0000000703c50b58
0x000000070a914860  1   3064    0x0000000709035198  dead    sun/reflect/DelegatingClassLoader@0x0000000703c50b58
0x000000070a9fc320  1   3056    0x0000000709035198  dead    sun/reflect/DelegatingClassLoader@0x0000000703c50b58
0x000000070adcb4c8  1   3064    0x0000000709035198  dead    sun/reflect/DelegatingClassLoader@0x0000000703c50b58
0x000000070a913760  1   1888    0x0000000709035198  dead    sun/reflect/DelegatingClassLoader@0x0000000703c50b58
0x0000000709f3fd40  1   3032      null      dead    sun/reflect/DelegatingClassLoader@0x0000000703c50b58
0x000000070923ba78  1   3088    0x0000000709035260  dead    sun/reflect/DelegatingClassLoader@0x0000000703c50b58
0x000000070a88fff8  1   3048      null      dead    sun/reflect/DelegatingClassLoader@0x0000000703c50b58
0x000000070adcbc58  1   1888    0x0000000709035198  dead    sun/reflect/DelegatingClassLoader@0x0000000703c50b58

-F

强制模式。如果指定的pid没有响应，请使用jmap -dump或jmap -histo选项。此模式下，不支持live子选项。







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