Java 虚拟机 jmap使用

也有很多开源的监控恐惧,本次只使用了jmap,了解简单使用,谢谢
开始了,922是我的tomcat进程

帮助命令查看,有哪些命令可以使用。

[root@bogon /]# 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
    -clstats             to print class loader 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

使用1:jmap pid 查看基本信息

[root@bogon /]# jmap 922
Attaching to process ID 922, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.111-b14
0x0000000000400000  7K  /usr/local/software/java/bin/java
0x0000003ddde00000  153K    /lib64/ld-2.12.so
0x0000003dde200000  22K /lib64/libdl-2.12.so
0x0000003dde600000  1881K   /lib64/libc-2.12.so
0x0000003ddea00000  142K    /lib64/libpthread-2.12.so
0x0000003ddee00000  45K /lib64/librt-2.12.so
0x0000003ddf200000  585K    /lib64/libm-2.12.so
0x0000003de0e00000  111K    /lib64/libresolv-2.12.so
0x0000003de9e00000  91K /lib64/libgcc_s-4.4.7-20120601.so.1
0x00007f90de586000  26K /lib64/libnss_dns-2.12.so
0x00007f913c39d000  250K    /usr/local/software/java/jre/lib/amd64/libsunec.so
0x00007f913cbf2000  90K /usr/local/software/java/jre/lib/amd64/libnio.so
0x00007f913d103000  113K    /usr/local/software/java/jre/lib/amd64/libnet.so
0x00007f913d31a000  49K /usr/local/software/java/jre/lib/amd64/libmanagement.so
0x00007f919a43b000  121K    /usr/local/software/java/jre/lib/amd64/libzip.so
0x00007f919a656000  64K /lib64/libnss_files-2.12.so
0x00007f919a874000  220K    /usr/local/software/java/jre/lib/amd64/libjava.so
0x00007f919aaa0000  64K /usr/local/software/java/jre/lib/amd64/libverify.so
0x00007f919acef000  16584K  /usr/local/software/java/jre/lib/amd64/server/libjvm.so
0x00007f919bce2000  100K    /usr/local/software/java/lib/amd64/jli/libjli.so

使用2 :查看堆信息,jmap -heap pid

[root@bogon /]# jmap -heap 922
Attaching to process ID 922, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.111-b14

using parallel threads in the new generation.  
using thread-local object allocation.
Concurrent Mark-Sweep GC

Heap Configuration:
   MinHeapFreeRatio         = 40
   MaxHeapFreeRatio         = 70
   MaxHeapSize              = 4294967296 (4096.0MB) 最大堆大小
   NewSize                  = 3221225472 (3072.0MB) 新生代大小
   MaxNewSize               = 3221225472 (3072.0MB) 最大分配新生代内存
   OldSize                  = 1073741824 (1024.0MB) 老年代大小
   NewRatio                 = 2 
   SurvivorRatio            = 8 新生代与老年代的比例
   MetaspaceSize            = 21807104 (20.796875MB) 
   CompressedClassSpaceSize = 1073741824 (1024.0MB)
   MaxMetaspaceSize         = 17592186044415 MB
   G1HeapRegionSize         = 0 (0.0MB)

Heap Usage: 堆的使用情况
New Generation (Eden + 1 Survivor Space): 新生代
   capacity = 2899116032 (2764.8125MB)
   used     = 384206560 (366.4079284667969MB)
   free     = 2514909472 (2398.404571533203MB)
   13.25254166301682% used
Eden Space: 新生代 eden区空间
   capacity = 2577006592 (2457.625MB)
   used     = 378654344 (361.11292266845703MB)
   free     = 2198352248 (2096.512077331543MB)
   14.693572968555294% used
From Space: 2个Survivor区域 其中一个就是这个from区
   capacity = 322109440 (307.1875MB)
   used     = 5552216 (5.295005798339844MB)
   free     = 316557224 (301.89249420166016MB)
   1.723704837709817% used
To Space:2个Survivor区域 其中一个就是这个to区
   capacity = 322109440 (307.1875MB)
   used     = 0 (0.0MB)
   free     = 322109440 (307.1875MB)
   0.0% used
concurrent mark-sweep generation: 老年代 eden区空间
   capacity = 1073741824 (1024.0MB)
   used     = 846734040 (807.5085067749023MB)
   free     = 227007784 (216.49149322509766MB)
   78.85825261473656% used

使用3:jmap -histo pid 查看一些class的使用情况,

jmap -histo 922
由于里面比较多内容,所以放弃了,可以自己使用一下,如果电脑展示不了一屏呢,可以这样。

jmap -histo 922  >dump.txt 导出文件,可以自己看了
下面是我自己导出的文件信息
 num     #instances(实例数量)         #bytes(字节)  class name 
----------------------------------------------
   1:        174069     1579369600  [C
   2:          4403      122732640  [I
   3:          9571       16889072  [B
   4:        157680        3784320  java.lang.String
   5:         38279        3674784  java.util.jar.JarFile$JarFileEntry
   6:         70982        2271424  java.util.HashMap$Node
   7:         13235        1164680  java.lang.reflect.Method
   8:          6001        1028952  [Ljava.util.HashMap$Node;

又或者可以过滤信息,命令:jmap -histo 922 |grep dubbo 过滤一下,就过滤你想要的信息

使用4:jmap -histo:live pid >dump.txt
这个和使用3差不多,都是在统计,只不过这个是在统计正在使用的对象,然后dump对象信息。

这种命令都是结合其它的命令一起使用的,以后会有文章结合一起分析,同学有什么好的工具也分享出来,一起学习,本篇只介绍jmap

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