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】
jmap --help
[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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命令格式
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
jmap -dump:live,format=b,file=dump.hprof 24971
[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
jmap -heap 24971
[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，
jmap -finalizerinfo 24971
[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: 0izer方法的对象。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
-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
jmap -histo:live 24971 | more
[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.Objectjmap -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。
jmap -permstat 24971
[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。