java-jvm-jmap(高内存排查)

功能：打印出某个java进程（使用pid）内存内的，所有‘对象’的情况（如：产生那些对象，及其数量）

-dump:[live,]format=b,file=<filename> 使用hprof二进制形式,输出jvm的heap内容到文件=. live子选项是可选的，假如指定live选项,那么只输出活的对象到文件.

-finalizerinfo 打印正等候回收的对象的信息.

-heap 打印heap的概要信息，GC使用的算法，heap的配置及wise heap的使用情况.

-histo[:live] 打印每个class的实例数目,内存占用,类全名信息. VM的内部类名字开头会加上前缀”*”. 如果live子参数加上后,只统计活的对象数量.

-permstat 打印classload和jvm heap长久层的信息. 包含每个classloader的名字,活泼性,地址,父classloader和加载的class数量. 另外,内部String的数量和占用内存数也会打印出来.


1、-heap
打印当前heap的概要信息：heap的总量，年轻代，老年代，Perm Generation的量
GC使用的算法
heap的配置：总量
当前heap的使用情况：占用量，总量，百分比
.

sudo jmap -heap 27409

输出：

Attaching to process ID 27409, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 24.45-b08

using thread-local object allocation.
Parallel GC with 4 thread(s)

Heap Configuration:
   MinHeapFreeRatio = 40
   MaxHeapFreeRatio = 70
   MaxHeapSize      = 2147483648 (2048.0MB)
   NewSize          = 268435456 (256.0MB)
   MaxNewSize       = 17592186044415 MB
   OldSize          = 5439488 (5.1875MB)
   NewRatio         = 2
   SurvivorRatio    = 8
   PermSize         = 268435456 (256.0MB)
   MaxPermSize      = 268435456 (256.0MB)
   G1HeapRegionSize = 0 (0.0MB)

Heap Usage:
PS Young Generation
Eden Space:
   capacity = 704643072 (672.0MB)
   used     = 429546320 (409.6472930908203MB)
   free     = 275096752 (262.3527069091797MB)
   60.959418614705406% used
From Space:
   capacity = 5767168 (5.5MB)
   used     = 4327344 (4.1268768310546875MB)
   free     = 1439824 (1.3731231689453125MB)
   75.03412420099431% used
To Space:
   capacity = 5767168 (5.5MB)
   used     = 0 (0.0MB)
   free     = 5767168 (5.5MB)
   0.0% used
PS Old Generation
   capacity = 1431830528 (1365.5MB)
   used     = 574251648 (547.6490478515625MB)
   free     = 857578880 (817.8509521484375MB)
   40.106118480524536% used
PS Perm Generation
   capacity = 268435456 (256.0MB)
   used     = 72128064 (68.78668212890625MB)
   free     = 196307392 (187.21331787109375MB)
   26.869797706604004% used

31742 interned Strings occupying 3432376 bytes.

2、-histo[:live] 打印每个class的实例数目,内存占用,类全名信息. VM的内部类名字开头会加上前缀”*”. 如果live子参数加上后,只统计活的对象数量.

sudo jmap -histo 27409>a.log

输出：

Object Histogram:

num       #instances    #bytes  Class description
--------------------------------------------------------------------------
1:              164294  173445488       byte[]
2:              4426453 106234872       java.util.concurrent.ConcurrentSkipListMap$Node
3:              448524  74384360        char[]
4:              2215688 53176512        java.lang.Double
5:              96356   33816408        int[]
6:              965084  23162016        java.util.concurrent.ConcurrentSkipListMap$Index
7:              125211  18655880        * ConstMethodKlass
8:              733892  17613408        java.lang.Long
9:              125211  16039712        * MethodKlass
10:             444730  14231360        java.util.HashMap$Entry
11:             11617   13094656        * ConstantPoolKlass
12:             426560  10237440        java.lang.String
13:             11611   8346592 * InstanceKlassKlass
14:             115808  7411712 com.mysql.jdbc.ConnectionPropertiesImpl$BooleanConnectionProperty
15:             9526    7374880 * ConstantPoolCacheKlass
。。。。

另外继续分析日志，每个对象存在的数量以及占用内存的大小：

grep "qunar" data.txt |grep "afare"

输出：

17:             28137   4051728 com.gym.afare.dubbo.model.AfareBlackList
664:            30      1680    com.gym.afare.dubbo.model.AfareBlackListPlus
977:            10      720     com.gym.flight.afare.model.RefreshCmRequest
1055:           12      576     com.gym.flight.afare.model.ErrorEnum
1099:           6       528     com.gym.afare.dubbo.model.request.AfareResultRequest
1146:           12      480     com.gym.flight.afare.model.RefreshTask
1151:           10      480     com.gym.flight.afare.model.RefreshPriceRequest
1206:           13      416     com.gym.flight.afare.model.ApiResponse
1480:           4       224     com.gym.afare.dubbo.model.AfareBlackList$FlightType[]
1544:           5       200     com.gym.afare.dubbo.model.AfareBlackList$UnLockTypeEnum
1574:           3       192     com.gym.afare.dubbo.model.AfareBlackList$UnLockTypeEnum[]
1596:           4       192     com.gym.afare.dubbo.model.AfareBlackList$FlightType
1666:           3       168     com.gym.afare.dubbo.model.AfareBlackList$LockTypeEnum[]
1841:           4       160     com.gym.afare.dubbo.model.AfareBlackList$LockTypeEnum
2015:           3       120     com.gym.afare.dubbo.model.AfareBlackList$LockStatusEnum[]
2022:           1       120     com.gym.flight.afare.model.ErrorEnum[]
2305:           2       80      com.gym.afare.dubbo.model.AfareBlackList$LockStatusEnum
2669:           1       56      com.gym.flight.afare.task.DeleteUnlockBlackListTask
2713:           1       48      com.gym.flight.afare.dubbo.provider.AfareBlackListServiceImpl
2952:           1       40      com.gym.flight.afare.dao.impl.AfareBlackListDAOImpl
2961:           1       40      com.gym.flight.afare.service.impl.RefreshPriceServiceImpl
3012:           1       40      com.gym.flight.afare.service.impl.RefreshPriceServiceImpl$RefreshThreadFactory
3036:           1       40      com.gym.flight.afare.dao.impl.AfareBlackListPlusDAOImpl
3182:           1       32      com.gym.flight.afare.dubbo.provider.AfareResultQueryServiceImpl
3197:           1       32      com.gym.flight.afare.dao.CacheManager
3282:           1       32      com.gym.flight.afare.dao.impl.AfareResultDaoImpl
3289:           1       32      com.gym.flight.afare.dubbo.provider.AfareResultUpdateServiceImpl
3292:           1       32      com.gym.flight.afare.service.Qc
3297:           1       32      com.gym.flight.afare.web.RefreshPriceController
3476:           1       24      com.gym.flight.afare.model.TaskListener
3479:           1       24      com.gym.flight.afare.task.ReloadBlacklistCacheTask
3543:           1       24      com.gym.flight.afare.task.ArchiveAfareResultTask
3676:           1       24      com.gym.flight.afare.dao.CacheManager$1
3720:           1       24      com.gym.flight.afare.web.BackController
4058:           1       16      com.gym.flight.afare.web.interceptor.TraceInterceptor
4119:           1       16      com.gym.flight.afare.util.SpringUtil

从中不难看出，SpringUtil 等类都是单例的，所以只有一个对象，而AfareBlackList 是系统内的对象，数量存在较多

3、-dump:[live,]format=b,file=<filename> 使用hprof二进制形式,输出jvm的heap内容到文件=. live子选项是可选的，假如指定live选项,那么只输出活的对象到文件.

sudo jmap -F -dump:live,format=b,file=heap.bin 27409

输出到heap.bin文件里
eg

class C{
	byte b = 100;
}

class B {
	List<C[]> d = new ArrayList<C[]>();

	public B() {
		for (int i = 0; i < 100000; i++) {
			d.add(new C[i]);
		}
	}

}

class A {
	List<B> bList = new ArrayList<B>();

	public A() {
		for (int i = 0; i < 1000; i++) {
			bList.add(new B());
		}
	}
}

public class Test {
	public static void main(String[] args) throws Exception {
		A a = new A();
		new Thread() {}.start();

		a.toString();
		
	}
}

运行参数：

-server -Xms1024m -Xmx1024m -Xmn512m -XX:+UseParallelOldGC -XX:+PrintGCApplicationStoppedTime -XX:+PrintGCDateStamps -XX:+PrintGCDetails  -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=c:/heap.bin

其他：
-permstat 打印classload和jvm heap长久层的信息. 包含每个classloader的名字,活泼性,地址,父classloader和加载的class数量. 另外,内部String的数量和占用内存数也会打印出来.
-dump:[live,]format=b,file=<filename> 使用hprof二进制形式,输出jvm的heap内容到文件=. live子选项是可选的，假如指定live选项,那么只输出活的对象到文件. 

参考资料：
http://www.tuicool.com/articles/VzYziu