JVM监控命令，常用

常用工具介绍:jinfo jmap jstack jstat

jinfo 

• 可以从一个给定的java进程或core文件或远程debug服务器上获取java配置信息。包括java系统属性及JVM参数(command line flags)。注意在jvm启动参数中没有配置的参数也可使用jinfo –flag xxx pid输出默认值(很有用,但貌似一些简写的参数查不出来)。
• 可以修改运行时的java 进程的opts。
• 只有solaris和linux的JDK版本里有。
• 使用方式可使用jinfo –h 查询。

jmap

       观察运行中的jvm物理内存的占用情况。

       如果连用SHELL jmap -histo pid>a.log可以将其保存到文本中去，在一段时间后，使用文本对比工具，可以对比出GC回收了哪些对象。

       参数很简单，直接查看jmap -h

       举例：

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

 

dump文件可以通过MemoryAnalyzer分析查看.网址： http://www.eclipse.org/mat/，可以查看dump时对象数量，内存占用，线程情况等。

jmap -dump:live为啥会触发Full GC

jstack

       观察jvm中当前所有线程的运行情况和线程当前状态

       如果java程序崩溃生成core文件，jstack工具可以用来获得core文件的java stack和native stack的信息，从而可以轻松地知道java程序是如何崩溃和在程序何处发生问题。另外，jstack工具还可以附属到正在运行的java程序中，看到当时运行的java程序的java stack和native stack的信息, 如果现在运行的java程序呈现hung的状态，jstack是非常有用的。目前只有在Solaris和Linux的JDK版本里面才有。

       参数很简单，直接查看jstack -h

       举例：

jstack pid

jstat

       JVM监测工具(Java Virtual Machine Statistics Monitoring Tool)。利用了JVM内建的指令对Java应用程序的资源和性能进行实时的命令行的监控，包括各种堆和非堆的大小及其内存使用量、classloader、compiler、垃圾回收状况等。

举例:

jstat –printcompilation -h10 3024 250 600

     每250毫秒打印一次，一共打印600次 每隔10行显示一次head

语法结构:

Usage: jstat -help|-options
       jstat -<option> [-t] [-h<lines>] <vmid> [<interval> [<count>]]

参数介绍：

• -h n 每隔几行输出标题
• vmid VM的进程号，即当前运行的java进程号
• -t 在第一列显示自JVM启动以来的时间戳
• -J 修改java进程的参数。类似jinfo -flag <name>=<value>。例如-J-Xms48m 设置初始堆为48M。详见这里。这个参数挺有用的，可以在运行中调整参数以方便测试、监测。
• -option option为要检测的参数。参数列表可通过jstat –options 获取。下面将分别介绍每个参数及输出字段的含义。

class	统计class loader行为信息
compiler	统计编译行为信息
gc	统计jdk gc时heap信息
gccapacity	统计堆内存不同代的heap容量信息
gccause	统计gc的情况（同-gcutil）和引起gc的事件
gcnew	统计gc时新生代的信息(相比gcutil更详细)
gcnewcapacity	统计gc时新生代heap容量
gcold	统计gc时，老年区的情况
gcoldcapacity	统计gc时，老年区heap容量
gcpermcapacity	统计gc时，permanent区heap容量
gcutil	统计gc时，heap情况
printcompilation	统计编译行为信息

-class option:Class Loader Statistics

Column	Description
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

Column	Description
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

Column	Description
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

Column	Description
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

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

       前面的字段与gcutil相同.

-gcnew Option:New Generation Statistics

Column	Description
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

Column	Description
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

Column	Description
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

Column	Description
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

Column	Description
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

Column	Description
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

Column	Description
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:+PrintComplationoption.