轉(zhuǎn)自本站：http://www.cnblogs.com/redcreen/archive/2011/05/09/2040977.html

?前幾篇篇文章介紹了介紹了JVM的參數(shù)設(shè)置并給出了一些生產(chǎn)環(huán)境的JVM參數(shù)配置參考方案。正如之前文章中提到的JVM參數(shù)的設(shè)置需要根據(jù)應(yīng)用的特性來進行設(shè)置，每個參數(shù)的設(shè)置都需要對JVM進行長時間的監(jiān)測，并不斷進行調(diào)整才能找到最佳設(shè)置方案。本文將介紹如果通過工具及Java api來監(jiān)測JVM的運行狀態(tài),并詳細介紹各工具的使用方法。

?????? 需要監(jiān)測的數(shù)據(jù)：(內(nèi)存使用情況 誰使用了內(nèi)存 GC的狀況)

內(nèi)存使用情況--heap&PermGen

@ 表示通過jmap –heap?pid?可以獲取的值

# 表示通過jstat –gcutil?pid?可以獲取的值

參數(shù)的查看可以通過多種方法 本文中只隨機列出一種。

描述	最大值	當前值	報警值
堆內(nèi)存	@Heap Configuration::MaxHeapSize sum(eden+servivor+old)	sum(eden+servivor+old)	自設(shè)
非堆內(nèi)存	sum(perm+native)	?	無
Eden	@Eden Space::capacity	@Eden Space::used	無
Survivor0	@From Space::capacity	@From Space::used	無
Survivor1	@To Space::capacity	@To Space::used	無
New gen (注意區(qū)別于Xmn參數(shù)設(shè)置)	@New Generation::capacity Eden + 1 Survivor Space	@New Generation::used	無
Old gen	@concurrent mark-sweep generation::capacity (CMS是對old區(qū)的gc,所以此處即表示old gen)	@concurrent mark-sweep generation::capacity(CMS)::used	自設(shè)
Perm Gen	@Perm Generation::capacity	@Perm Generation::used	自設(shè)

內(nèi)存使用情況--config

描述	配置值
MaxTenuringThreshold	jinfo -flag MaxTenuringThreshold?pid
MinHeapFreeRatio	@Heap Configuration::MinHeapFreeRatio
MaxHeapFreeRatio	@Heap Configuration::MaxHeapFreeRatio
new gen gc	@using … in the new generation
old gen gc	new gen gc聲明下方
類總數(shù)統(tǒng)計	??

內(nèi)存使用情況—C heap

• top or ps aux

誰使用了內(nèi)存

• Heap
  jmap –histo
  jmap –dump ,then mat
• C heap
  google perftools

GC的狀況

描述	收集次數(shù)	收集時間	應(yīng)用暫停時間
Full GC	#FGC	#FGCT	設(shè)置-XX:+PrintGCApplicationStoppedTime后在日志中查看
Young GC	#YGC	#YGCT	同上

-XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintHeapAtGC??-XX:+PrintGCApplicationStoppedTime? -Xloggc:logs/gc.log

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常用工具介紹:jinfo jmap jstack jstat

jinfo?

• 可以從一個給定的java進程或core文件或遠程debug服務(wù)器上獲取java配置信息。包括java系統(tǒng)屬性及JVM參數(shù)(command line flags)。注意在jvm啟動參數(shù)中沒有配置的參數(shù)也可使用jinfo –flag xxx pid輸出默認值(很有用,但貌似一些簡寫的參數(shù)查不出來)。
• 可以修改運行時的java 進程的opts。
• 只有solaris和linux的JDK版本里有。
• 使用方式可使用jinfo –h 查詢。

jmap

?????? 觀察運行中的jvm物理內(nèi)存的占用情況。

?????? 如果連用SHELL jmap -histo pid>a.log可以將其保存到文本中去，在一段時間后，使用文本對比工具，可以對比出GC回收了哪些對象。

?????? 參數(shù)很簡單，直接查看jmap -h

?????? 舉例：

jmap -heap pid

jmap -dump:format=b,file=heap.hprof <pid>

dump文件可以通過MemoryAnalyzer分析查看.網(wǎng)址：http://www.eclipse.org/mat/，可以查看dump時對象數(shù)量，內(nèi)存占用，線程情況等。 jmap -dump:live為啥會觸發(fā)Full GC

jstack

?????? 觀察jvm中當前所有線程的運行情況和線程當前狀態(tài)

?????? 如果java程序崩潰生成core文件，jstack工具可以用來獲得core文件的java stack和native stack的信息，從而可以輕松地知道java程序是如何崩潰和在程序何處發(fā)生問題。另外，jstack工具還可以附屬到正在運行的java程序中，看到當時運行的java程序的java stack和native stack的信息, 如果現(xiàn)在運行的java程序呈現(xiàn)hung的狀態(tài)，jstack是非常有用的。目前只有在Solaris和Linux的JDK版本里面才有。

?????? 參數(shù)很簡單，直接查看jstack -h

?????? 舉例：

jstack pid

jstat

?????? JVM監(jiān)測工具(Java Virtual Machine Statistics Monitoring Tool)。利用了JVM內(nèi)建的指令對Java應(yīng)用程序的資源和性能進行實時的命令行的監(jiān)控，包括各種堆和非堆的大小及其內(nèi)存使用量、classloader、compiler、垃圾回收狀況等。

舉例:

jstat –printcompilation -h10 3024 250 600

???? 每250毫秒打印一次，一共打印600次 每隔10行顯示一次head

語法結(jié)構(gòu): Usage: jstat -help|-options
jstat -<option> [-t] [-h<lines>] <vmid> [<interval> [<count>]]

參數(shù)介紹：

• -h n 每隔幾行輸出標題
• vmid VM的進程號，即當前運行的java進程號
• -t 在第一列顯示自JVM啟動以來的時間戳
• -J 修改java進程的參數(shù)。類似jinfo -flag <name>=<value>。例如-J-Xms48m?設(shè)置初始堆為48M。詳見這里。這個參數(shù)挺有用的，可以在運行中調(diào)整參數(shù)以方便測試、監(jiān)測。
• -option option為要檢測的參數(shù)。參數(shù)列表可通過jstat –options 獲取。下面將分別介紹每個參數(shù)及輸出字段的含義。

class	統(tǒng)計class loader行為信息
compiler	統(tǒng)計編譯行為信息
gc	統(tǒng)計jdk gc時heap信息
gccapacity	統(tǒng)計堆內(nèi)存不同代的heap容量信息
gccause	統(tǒng)計gc的情況（同-gcutil）和引起gc的事件
gcnew	統(tǒng)計gc時新生代的信息(相比gcutil更詳細)
gcnewcapacity	統(tǒng)計gc時新生代heap容量
gcold	統(tǒng)計gc時，老年區(qū)的情況
gcoldcapacity	統(tǒng)計gc時，老年區(qū)heap容量
gcpermcapacity	統(tǒng)計gc時，permanent區(qū)heap容量
gcutil	統(tǒng)計gc時，heap情況
printcompilation	統(tǒng)計編譯行為信息

-class option:Class Loader Statistics

ColumnDescription

Loaded	Number of classes loaded.
Bytes	Number of Kbytes loaded.
Unloaded	Number of classes unloaded.
Bytes	Number of Kbytes unloaded.
Time	Time spent performing class load and unload operations.

-compiler:HotSpot Just-In-Time Compiler Statistics

ColumnDescription

Compiled	Number of compilation tasks performed.
Failed	Number of compilation tasks that failed.
Invalid	Number of compilation tasks that were invalidated.
Time	Time spent performing compilation tasks.
FailedType	Compile type of the last failed compilation.
FailedMethod	Class name and method for the last failed compilation.

-gc Option:Garbage-collected heap statistics

ColumnDescription

S0C	Current survivor space 0 capacity (KB).
S1C	Current survivor space 1 capacity (KB).
S0U	Survivor space 0 utilization (KB).
S1U	Survivor space 1 utilization (KB).
EC	Current eden space capacity (KB).
EU	Eden space utilization (KB).
OC	Current old space capacity (KB).
OU	Old space utilization (KB).
PC	Current permanent space capacity (KB).
PU	Permanent space utilization (KB).
YGC	Number of young generation GC Events.
YGCT	Young generation garbage collection time.
FGC	Number of full GC events.
FGCT	Full garbage collection time.
GCT	Total garbage collection time.

-gccapacity Option:Memory Pool Generation and Space Capacities

ColumnDescription

NGCMN	Minimum new generation capacity (KB).
NGCMX	Maximum new generation capacity (KB).
NGC	Current new generation capacity (KB).
S0C	Current survivor space 0 capacity (KB).
S1C	Current survivor space 1 capacity (KB).
EC	Current eden space capacity (KB).
OGCMN	Minimum old generation capacity (KB).
OGCMX	Maximum old generation capacity (KB).
OGC	Current old generation capacity (KB).
OC	Current old space capacity (KB).
PGCMN	Minimum permanent generation capacity (KB).
PGCMX	Maximum Permanent generation capacity (KB).
PGC	Current Permanent generation capacity (KB).
PC	Current Permanent space capacity (KB).
YGC	Number of Young generation GC Events.
FGC	Number of Full GC Events.

-gccause Option:Garbage Collection Statistics, Including GC Events

ColumnDescription

LGCC	Cause of last Garbage Collection.
GCC	Cause of current Garbage Collection.

?????? 前面的字段與gcutil相同.

-gcnew Option:New Generation Statistics

ColumnDescription

S0C	Current survivor space 0 capacity (KB).
S1C	Current survivor space 1 capacity (KB).
S0U	Survivor space 0 utilization (KB).
S1U	Survivor space 1 utilization (KB).
TT	Tenuring threshold.
MTT	Maximum tenuring threshold.
DSS	Desired survivor size (KB).
EC	Current eden space capacity (KB).
EU	Eden space utilization (KB).
YGC	Number of young generation GC events.
YGCT	Young generation garbage collection time.

-gcnewcapacity Option:New Generation Space Size Statistics

ColumnDescription

NGCMN???????????	Minimum new generation capacity (KB).?
NGCMX????	Maximum new generation capacity (KB).
NGC????	Current new generation capacity (KB).
S0CMX	Maximum survivor space 0 capacity (KB).
S0C	Current survivor space 0 capacity (KB).
S1CMX	Maximum survivor space 1 capacity (KB).
S1C	Current survivor space 1 capacity (KB).
ECMX	Maximum eden space capacity (KB).
EC	Current eden space capacity (KB).
YGC	Number of young generation GC events.
FGC	Number of Full GC Events.

-gcold Option:Old and Permanent Generation Statistics

ColumnDescription

PC	Current permanent space capacity (KB).
PU	Permanent space utilization (KB).
OC	Current old space capacity (KB).
OU	old space utilization (KB).
YGC	Number of young generation GC events.
FGC	Number of full GC events.
FGCT	Full garbage collection time.
GCT	Total garbage collection time.

-gcoldcapacity Option:Old Generation Statistics

ColumnDescription

OGCMN	Minimum old generation capacity (KB).
OGCMX	Maximum old generation capacity (KB).
OGC	Current old generation capacity (KB).
OC	Current old space capacity (KB).
YGC	Number of young generation GC events.
FGC	Number of full GC events.
FGCT	Full garbage collection time.
GCT	Total garbage collection time.

-gcpermcapacity Option: Permanent Generation Statistics

ColumnDescription

PGCMN	Minimum permanent generation capacity (KB).
PGCMX	Maximum permanent generation capacity (KB).
PGC	Current permanent generation capacity (KB).
PC	Current permanent space capacity (KB).
YGC	Number of young generation GC events.
FGC	Number of full GC events.
FGCT	Full garbage collection time.
GCT	Total garbage collection time.

-gcutil Option:Summary of Garbage Collection Statistics

ColumnDescription

S0	Survivor space 0 utilization as a percentage of the space's current capacity.
S1	Survivor space 1 utilization as a percentage of the space's current capacity.
E	Eden space utilization as a percentage of the space's current capacity.
O	Old space utilization as a percentage of the space's current capacity.
P	Permanent space utilization as a percentage of the space's current capacity.
YGC	Number of young generation GC events.
YGCT	Young generation garbage collection time.
FGC	Number of full GC events.
FGCT	Full garbage collection time.
GCT	Total garbage collection time.

-printcompilation Option: HotSpot Compiler Method Statistics

ColumnDescription

Compiled	Number of compilation tasks performed.
Size	Number of bytes of bytecode for the method.
Type	Compilation type.
Method	Class name and method name identifying the compiled method. Class name uses "/" instead of "." as namespace separator. Method name is the method within the given class. The format for these two fields is consistent with the HotSpot -?XX:+PrintComplation?option.

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Java api方式監(jiān)測

?????? jre中提供了一些查看運行中的jvm內(nèi)部信息的api，這些api包含在java.lang.management包中，此包中的接口是在jdk 5中引入的，所以只有在jdk 5及其以上版本中才能通過這種方式訪問這些信息。下面簡單介紹一下這包括哪些信息，以及如何訪問。

?????? 可以通過此api訪問到運行中的jvm的類加載的信息、jit編譯器的信息、內(nèi)存分配的情況、線程的相關(guān)信息以及運行jvm的操作系統(tǒng)的信息。java.lang.management包中提供了9個接口來訪問這些信息，使用ManagementFactory的靜態(tài)get方法可以獲得相應(yīng)接口的實例，可以通過這些實例來獲取你需要的相關(guān)信息。

?????? 更詳細的關(guān)于MBean的介紹參見Java SE 6 新特性: JMX 與系統(tǒng)管理

?????? demo1:查看一下當前運行的jvm中加載了多少個類。想詳細了解如何使用這些api，可以參考java.lang.management包中的詳細api文檔。

public class ClassLoaderChecker {
public static void main( String[] args ) throws Exception {
????? ClassLoadingMXBean bean = ManagementFactory.getClassLoadingMXBean();
????? System.out.println( bean.getLoadedClassCount() );
??? }
} demo2:自定義Mbean Type,記錄的數(shù)據(jù)可通過jconsole等工具或自寫代碼查看,

//工具方法

public static ObjectName register(String name, Object mbean) {
try {
ObjectName objectName = new ObjectName(name);

MBeanServer mbeanServer = ManagementFactory
.getPlatformMBeanServer();

try {
mbeanServer.registerMBean(mbean, objectName);
} catch (InstanceAlreadyExistsException ex) {
mbeanServer.unregisterMBean(objectName);
mbeanServer.registerMBean(mbean, objectName);
}

return objectName;
} catch (JMException e) {
throw new IllegalArgumentException(name, e);
}
}

//步驟一:定義Mbean接口: //隨便定義 public interface DemoMBean { public AtomicLong getInvokeCount(); } //步驟二:實現(xiàn)接口,并注冊: public class DemoImpl implements DemoMBean{ public final static String DEFAULT_OBJECT_NAME_PREFIX = "com.redcreen.demo:type=demo"; register("com.redcreen.demo:type=demo",DemoImpl.instance); } //可以通過jconsole中查看數(shù)據(jù)了

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在 Java SE 6 中監(jiān)視和診斷性能問題

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參考:

http://www.51testing.com/?uid-183198-action-viewspace-itemid-185174

JVM監(jiān)控工具介紹jstack, jconsole, jinfo, jmap, jdb, jstat

http://stl-www.htw-saarland.de/syst-lab/java/jdk-1_5_0/docs/tooldocs/share/jinfo.html

http://qa.taobao.com/?p=10010

運用Jconsole監(jiān)控JVM

http://www.coderanch.com/t/329407/java/java/find-all-loaded-classes-classloaders

轉(zhuǎn)載于:https://www.cnblogs.com/southdom/articles/5001707.html

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