jvm信息jmap使用的基本方法教程

前言

大家都知道有很多开源的监控工具，本次只使用了jmap，了解简单使用，谢谢，下面话不多说了，来一起看看详细的介绍吧

使用方法如下：

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

总结

以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作具有一定的参考学习价值，如果有疑问大家可以留言交流，谢谢大家对的支持。