【Java命令一】jmap

jmap命令的用法：

 

[hadoop@hadoop sbin]$ jmap
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

 

jmap可以对本机或者远程机器正在运行的Java程序的内存使用情况进行分析

常用用法：

 

1.jmap pid

结果：这个结果显示，第二列是文件大小，第三列是具体的文件

 

 

0x0000000000400000	7K	/home/hadoop/software/jdk1.7.0_67/bin/java
0x00007ff9ac9ac000	108K	/usr/lib64/libresolv-2.17.so
0x00007ff9acbc6000	26K	/usr/lib64/libnss_dns-2.17.so
0x00007ff9c819c000	112K	/home/hadoop/software/jdk1.7.0_67/jre/lib/amd64/libnet.so
0x00007ff9c83b3000	89K	/home/hadoop/software/jdk1.7.0_67/jre/lib/amd64/libnio.so
0x00007ff9d2e31000	120K	/home/hadoop/software/jdk1.7.0_67/jre/lib/amd64/libzip.so
0x00007ff9d304c000	56K	/usr/lib64/libnss_files-2.17.so
0x00007ff9d3258000	214K	/home/hadoop/software/jdk1.7.0_67/jre/lib/amd64/libjava.so
0x00007ff9d3483000	63K	/home/hadoop/software/jdk1.7.0_67/jre/lib/amd64/libverify.so
0x00007ff9d3691000	43K	/usr/lib64/librt-2.17.so
0x00007ff9d3899000	1114K	/usr/lib64/libm-2.17.so
0x00007ff9d3b9b000	14853K	/home/hadoop/software/jdk1.7.0_67/jre/lib/amd64/server/libjvm.so
0x00007ff9d4a0f000	2058K	/usr/lib64/libc-2.17.so
0x00007ff9d4dd0000	19K	/usr/lib64/libdl-2.17.so
0x00007ff9d4fd4000	103K	/home/hadoop/software/jdk1.7.0_67/lib/amd64/jli/libjli.so
0x00007ff9d51eb000	138K	/usr/lib64/libpthread-2.17.so
0x00007ff9d5407000	156K	/usr/lib64/ld-2.17.so

 

 

2.jmap -heap pid(堆内存使用详细情况)

 

 

[hadoop@hadoop sbin]$ jmap -heap 1819
Attaching to process ID 1819, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 24.65-b04

using thread-local object allocation.
Parallel GC with 2 thread(s)

Heap Configuration:
   MinHeapFreeRatio = 0
   MaxHeapFreeRatio = 100
   MaxHeapSize      = 536870912 (512.0MB)
   NewSize          = 1310720 (1.25MB)
   MaxNewSize       = 17592186044415 MB
   OldSize          = 5439488 (5.1875MB)
   NewRatio         = 2
   SurvivorRatio    = 8
   PermSize         = 21757952 (20.75MB)
   MaxPermSize      = 134217728 (128.0MB)
   G1HeapRegionSize = 0 (0.0MB)

Heap Usage:
PS Young Generation
Eden Space:
   capacity = 135266304 (129.0MB)
   used     = 31579760 (30.116806030273438MB)
   free     = 103686544 (98.88319396972656MB)
   23.346361263777858% used
From Space:
   capacity = 22020096 (21.0MB)
   used     = 17629120 (16.81243896484375MB)
   free     = 4390976 (4.18756103515625MB)
   80.05923316592262% used
To Space:
   capacity = 22020096 (21.0MB)
   used     = 0 (0.0MB)
   free     = 22020096 (21.0MB)
   0.0% used
PS Old Generation
   capacity = 358088704 (341.5MB)
   used     = 8192 (0.0078125MB)
   free     = 358080512 (341.4921875MB)
   0.002287701317715959% used
PS Perm Generation
   capacity = 24641536 (23.5MB)
   used     = 24625520 (23.484725952148438MB)
   free     = 16016 (0.0152740478515625MB)
   99.93500405169547% used

3509 interned Strings occupying 266432 byte

 

 

• Heap Configuration:堆内存空间的分配参数，
• Heap Usage：堆的各个空间的内存使用情况

3. 将内存使用情况dump到磁盘(可以运行时执行）

 

jmap -dump:file=heap.dump.bin.001 1819

 

[hadoop@hadoop sbin]$ jmap -dump:file=heap.dump.bin.001 1819
Dumping heap to /home/hadoop/software/spark-1.2.0-bin-hadoop2.4/sbin/heap.dump.bin.001 ...
Heap dump file created
[hadoop@hadoop sbin]$ ls -lh
total 108M
-rw-------  1 hadoop hadoop  42M Feb 27 05:02 headop.bin
-rw-------  1 hadoop hadoop  66M Feb 27 05:21 heap.dump.bin.001

速度非常快，dump的大小为66M，接下来的问题，如何分析这个dump文件

 

 

4. 使用jhat

 

[hadoop@hadoop sbin]$ jhat
ERROR: No arguments supplied
Usage:  jhat [-stack <bool>] [-refs <bool>] [-port <port>] [-baseline <file>] [-debug <int>] [-version] [-h|-help] <file>

	-J<flag>          Pass <flag> directly to the runtime system. For
			  example, -J-mx512m to use a maximum heap size of 512MB
	-stack false:     Turn off tracking object allocation call stack.
	-refs false:      Turn off tracking of references to objects
	-port <port>:     Set the port for the HTTP server.  Defaults to 7000
	-exclude <file>:  Specify a file that lists data members that should
			  be excluded from the reachableFrom query.
	-baseline <file>: Specify a baseline object dump.  Objects in
			  both heap dumps with the same ID and same class will
			  be marked as not being "new".
	-debug <int>:     Set debug level.
			    0:  No debug output
			    1:  Debug hprof file parsing
			    2:  Debug hprof file parsing, no server
	-version          Report version number
	-h|-help          Print this help and exit
	<file>            The file to read

For a dump file that contains multiple heap dumps,
you may specify which dump in the file
by appending "#<number>" to the file name, i.e. "foo.hprof#3".

All boolean options default to "true"
[hadoop@hadoop sbin]$ jhat heap.dump.bin.001  //分析heap文件
Reading from heap.dump.bin.001...
Dump file created Fri Feb 27 05:21:39 EST 2015
Snapshot read, resolving...
Resolving 633856 objects...
Chasing references, expect 126 dots..............................................................................................................................
Eliminating duplicate references..............................................................................................................................
Snapshot resolved.
Started HTTP server on port 7000
Server is ready.

 可以通过7000端口打开http server进行查看每个对象占用的空间

 

 

5.显示永久代的统计信息

jmap -permstat pid

 

 

[hadoop@hadoop sbin]$ jmap -permstat 1819
Attaching to process ID 1819, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 24.65-b04
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>	       1121	6558096	  null  	live	<internal>
0x00000000fd818900	1	3048	0x00000000fd662860	dead	sun/reflect/DelegatingClassLoader@0x00000000d7fcfc00
0x00000000fd92afc0	0	0	0x00000000fd662860	dead	java/util/ResourceBundle$RBClassLoader@0x00000000d8614b60
0x00000000fd818940	1	3048	  null  	dead	sun/reflect/DelegatingClassLoader@0x00000000d7fcfc00
0x00000000fd6628b0	0	0	  null  	dead	sun/misc/Launcher$ExtClassLoader@0x00000000d8135e68
0x00000000fd818980	1	3048	0x00000000fd662860	dead	sun/reflect/DelegatingClassLoader@0x00000000d7fcfc00
0x00000000fd662860	3051	19694968	0x00000000fd6628b0	dead	sun/misc/Launcher$AppClassLoader@0x00000000d81935f0
0x00000000fd8189c0	1	1888	  null  	dead	sun/reflect/DelegatingClassLoader@0x00000000d7fcfc00
0x00000000fd8188c0	1	3048	0x00000000fd662860	dead	sun/reflect/DelegatingClassLoader@0x00000000d7fcfc00

total = 9	4177	26267144	    N/A    	alive=1, dead=8	    N/A