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

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

[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

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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

[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