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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[root@localhost 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] [server_id@]<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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[root@localhost 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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[root@localhost 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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[root@localhost 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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[root@localhost 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 Character	Type	Interpretation
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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[root@localhost 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。