探索Java内置的性能检测神器：jmap
最编程
2024-02-10 14:42:32
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本文继续介绍Java自带的性能监测工具，本文使用jmap工具来玩~
jmap (Java Memory Map) 命令可以生成Java应用程序的堆快照和对象统计信息，对生成的堆快照进行分析，可以分析堆中对象所占用内存的情况，检查大对象等~
先使用jmap -help查看一下jmap命令的基本语法以及选择项（option）说明~
[root@dev18 ~]# 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
[root@dev18 ~]#jmap基本语法：
jmap [option] <pid>jmap需要pid，所以需要和jps配合使用，也就是先使用jps获取pid信息，然后使用jmap来处理~
[root@dev18 ~]# jps -l
1656 org.elasticsearch.bootstrap.Elasticsearch
12905 org.apache.zookeeper.server.quorum.QuorumPeerMain
4308 /srv/activemq/apache-activemq-5.14.3//bin/activemq.jar
27265 sun.tools.jps.Jps
[root@dev18 ~]#
接下来，本文使用Zookeeper的服务进程为例，其pid为12905
使用 jmap -heap 12905打印java heap的情况，如
[root@dev18 ~]# jmap -heap 12905
Attaching to process ID 12905, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 24.71-b01
using thread-local object allocation.
Parallel GC with 2 thread(s)
Heap Configuration:
MinHeapFreeRatio = 0
MaxHeapFreeRatio = 100
MaxHeapSize = 1004535808 (958.0MB)
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 = 15204352 (14.5MB)
used = 12229848 (11.663291931152344MB)
free = 2974504 (2.8367080688476562MB)
80.43649607691272% used
From Space:
capacity = 524288 (0.5MB)
used = 32768 (0.03125MB)
free = 491520 (0.46875MB)
6.25% used
To Space:
capacity = 524288 (0.5MB)
used = 0 (0.0MB)
free = 524288 (0.5MB)
0.0% used
PS Old Generation
capacity = 41418752 (39.5MB)
used = 3584192 (3.41815185546875MB)
free = 37834560 (36.08184814453125MB)
8.65354900118671% used
PS Perm Generation
capacity = 22020096 (21.0MB)
used = 8938800 (8.524703979492188MB)
free = 13081296 (12.475296020507812MB)
40.59382847377232% used
2776 interned Strings occupying 230000 bytes.
[root@dev18 ~]# 使用 jmap -histo打印jvm heap的直方图。其输出信息包括类名，对象数量，对象占用大小。
下面的例子使用jmap生成pid为12905的Java程序的对象统计信息（直方图的形式），并将生成的统计信息输出到时/usr/local目录下的12905.histo文件中，如：
[root@dev18 ~]# jmap -histo 12905 >/usr/local/12905.histo打开12905.histo文件，查看详细的信息如：
[root@dev18 ~]# vim /usr/local/12905.histo num #instances #bytes class name
----------------------------------------------
1: 30204 5384536 [B
2: 17521 2252160 <methodKlass>
3: 17521 2186552 <constMethodKlass>
4: 1515 1644272 <constantPoolKlass>
5: 39568 1582720 java.util.HashMap$KeyIterator
6: 10809 1457680 [C
7: 1515 1040840 <instanceKlassKlass>
8: 1368 1032128 <constantPoolCacheKlass>
9: 40162 919944 [Ljava.lang.Object;
10: 36461 875064 java.util.ArrayList
11: 35427 850248 java.lang.Long
12: 15953 765744 java.nio.HeapByteBuffer
13: 5384 387648 org.apache.zookeeper.server.Request
14: 11669 373408 java.util.HashMap$Entry
15: 3771 301296 [Ljava.util.HashMap$Entry;
16: 612 296376 [I
17: 5687 272976 java.util.HashMap
18: 3805 254448 [S
19: 7029 224928 java.util.concurrent.locks.AbstractQueuedSynchronizer$Node
20: 453 203136 <methodDataKlass>
21: 7138 171312 java.util.concurrent.LinkedBlockingQueue$Node
22: 7008 168192 java.lang.String
23: 1671 161696 java.lang.Class
24: 2507 133624 [[I
25: 5223 125352 java.util.Collections$UnmodifiableRandomAccessList
26: 3513 112416 java.io.DataInputStream
27: 3513 112416 java.io.DataOutputStream
28: 3511 112352 org.apache.zookeeper.proto.ReplyHeader
29: 1872 89856 org.apache.zookeeper.txn.TxnHeader
30: 5486 87776 java.util.HashSet
31: 3513 84312 org.apache.jute.BinaryOutputArchive
32: 3512 84288 java.io.ByteArrayOutputStream
33: 139 75616 <objArrayKlassKlass>
34: 1506 72288 org.apache.zookeeper.KeeperException$NodeExistsException
35: 1871 59872 org.apache.zookeeper.server.quorum.QuorumPacket
36: 3561 56976 java.util.HashMap$KeySet
37: 3513 56208 org.apache.zookeeper.server.ByteBufferInputStream
38: 3513 56208 org.apache.jute.BinaryInputArchive
39: 3512 56192 org.apache.zookeeper.server.SessionTrackerImpl$SessionSet
40: 1873 44952 java.util.LinkedList$Node
41: 1871 44904 org.apache.zookeeper.server.quorum.Leader$Proposal
42: 516 41280 java.lang.reflect.Method
43: 1045 33440 java.util.concurrent.ConcurrentHashMap$HashEntry
44: 1694 27104 java.lang.Object
45: 1506 24096 org.apache.zookeeper.txn.ErrorTxn
46: 106 16960 org.apache.zookeeper.server.NIOServerCnxn
47: 426 13632 java.util.concurrent.locks.ReentrantLock$NonfairSync
48: 230 12704 [Ljava.util.concurrent.ConcurrentHashMap$HashEntry;#instances, #bytes以及class name列说明：
instances列：表示当前类有多少个实例。
bytes列：说明当前类的实例总共占用了多少个字节
class name列：表示的就是当前类的名称，class name 解读：
B代表byte
C代表char
D代表double
F代表float
I代表int
J代表long
Z代表boolean
前边有[代表数组，[I 就相当于int[]
对象用[L+类名表示 也可以不生成文件，直接使用jmap -histo 12905查看，因为内容比较多，可以采用添加| more来限定~
[root@dev18 ~]# jmap -histo 12905 | more
num #instances #bytes class name
----------------------------------------------
1: 30330 5407864 [B
2: 17521 2252160 <methodKlass>
3: 17521 2186552 <constMethodKlass>
4: 1515 1644272 <constantPoolKlass>
5: 39770 1590800 java.util.HashMap$KeyIterator
6: 10827 1460848 [C
7: 1515 1040840 <instanceKlassKlass>
8: 1368 1032128 <constantPoolCacheKlass>
9: 40346 923032 [Ljava.lang.Object;
10: 36645 879480 java.util.ArrayList
11: 35608 854592 java.lang.Long
12: 16025 769200 java.nio.HeapByteBuffer
13: 5402 388944 org.apache.zookeeper.server.Request
14: 11723 375136 java.util.HashMap$Entry
15: 613 357464 [I
16: 3789 302736 [Ljava.util.HashMap$Entry;
17: 5705 273840 java.util.HashMap
18: 3805 254448 [S
19: 7065 226080 java.util.concurrent.locks.AbstractQueuedSynchronizer$Node
20: 453 203136 <methodDataKlass>
21: 7174 172176 java.util.concurrent.LinkedBlockingQueue$Node
22: 7008 168192 java.lang.String
23: 1671 161696 java.lang.Class
24: 2507 133624 [[I
25: 5241 125784 java.util.Collections$UnmodifiableRandomAccessList
26: 3531 112992 java.io.DataInputStream
27: 3531 112992 java.io.DataOutputStream
28: 3529 112928 org.apache.zookeeper.proto.ReplyHeader
29: 1872 89856 org.apache.zookeeper.txn.TxnHeader
30: 5504 88064 java.util.HashSet
31: 3531 84744 org.apache.jute.BinaryOutputArchive
32: 3530 84720 java.io.ByteArrayOutputStream
33: 139 75616 <objArrayKlassKlass>
34: 1506 72288 org.apache.zookeeper.KeeperException$NodeExistsException
35: 1871 59872 org.apache.zookeeper.server.quorum.QuorumPacket
36: 3579 57264 java.util.HashMap$KeySet
37: 3531 56496 org.apache.zookeeper.server.ByteBufferInputStream
38: 3531 56496 org.apache.jute.BinaryInputArchive
39: 3530 56480 org.apache.zookeeper.server.SessionTrackerImpl$SessionSet
40: 1873 44952 java.util.LinkedList$Node
41: 1871 44904 org.apache.zookeeper.server.quorum.Leader$Proposal
42: 516 41280 java.lang.reflect.Method
43: 1045 33440 java.util.concurrent.ConcurrentHashMap$HashEntry
44: 1694 27104 java.lang.Object
45: 1506 24096 org.apache.zookeeper.txn.ErrorTxn
46: 106 16960 org.apache.zookeeper.server.NIOServerCnxn
47: 426 13632 java.util.concurrent.locks.ReentrantLock$NonfairSync
48: 230 12704 [Ljava.util.concurrent.ConcurrentHashMap$HashEntry;
49: 308 12320 java.lang.ref.SoftReference使用jmap -permstat 12905打印permanent generation heap情况
[root@dev18 ~]# jmap -permstat 12905
Attaching to process ID 12905, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 24.71-b01
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> 1267 7343336 null live <internal>
0x00000000c4292130 1 3048 null dead sun/reflect/DelegatingClassLoader@0x00000000bf04ffc8
0x00000000c420b210 0 0 null dead sun/misc/Launcher$ExtClassLoader@0x00000000bf1c0120
0x00000000c4292170 1 1888 null dead sun/reflect/DelegatingClassLoader@0x00000000bf04ffc8
0x00000000c42921b0 1 1888 null dead sun/reflect/DelegatingClassLoader@0x00000000bf04ffc8
0x00000000c4292358 2 32144 null dead javax/management/remote/rmi/NoCallStackClassLoader@0x00000000bf546b68
0x00000000c42921f0 1 1888 null dead sun/reflect/DelegatingClassLoader@0x00000000bf04ffc8
0x00000000c420b1c0 401 2657256 0x00000000c420b210 dead sun/misc/Launcher$AppClassLoader@0x00000000bf21a9c8
0x00000000c42920e0 4 13776 null dead javax/management/remote/rmi/NoCallStackClassLoader@0x00000000bf546b68
0x00000000c4292318 1 3048 null dead sun/reflect/DelegatingClassLoader@0x00000000bf04ffc8
0x00000000c42922d8 1 1888 null dead sun/reflect/DelegatingClassLoader@0x00000000bf04ffc8
0x00000000c4292298 1 3048 null dead sun/reflect/DelegatingClassLoader@0x00000000bf04ffc8
0x00000000c4312bc8 0 0 0x00000000c420b1c0 dead java/util/ResourceBundle$RBClassLoader@0x00000000bf6dce70
0x00000000c4292258 1 3056 null dead sun/reflect/DelegatingClassLoader@0x00000000bf04ffc8
total = 14 1682 10066264 N/A alive=1, dead=13 N/A
[root@dev18 ~]# jmap还有一个功能是可以手工生成指定程序的堆快照文件~ 使用-dump选项~
如：
jmap -dump:format=b,file=/usr/local/12905.hprof 12905该示例为pid为12905的程序生成一个二进制的dump文件，文件放置在/usr/local目录下， 名字为12905.hprof~
[root@dev18 ~]# jmap -dump:format=b,file=/usr/local/12905.hprof 12905
Dumping heap to /usr/local/12905.hprof ...
Heap dump file created
[root@dev18 ~]#
针对这种产生的dump文件，可以使用JDK自带jhat(Java Heap Analyse Tool)小工具来查看，可以将对中的对象以html的形式展示，包括对象的数量、大小等信息，并支持对象查询语言 （OQL），jhat将会在下一篇文章中介绍~