前几篇篇文章介绍了介绍了JVM的参数设置并给出了一些生产环境的JVM参数配置参考方案。正如之前文章中提到的JVM参数的设置需要根据应用的特性来进行设置，每个参数的设置都需要对JVM进行长时间的监测，并不断进行调整才能找到最佳设置方案。本文将介绍如果通过工具及Java api来监测JVM的运行状态,并详细介绍各工具的使用方法。
需要监测的数据：(内存使用情况 谁使用了内存 GC的状况)
内存使用情况--heap&PermGen
@ 表示通过jmap –heap pid 可以获取的值
# 表示通过jstat –gcutil pid 可以获取的值
参数的查看可以通过多种方法 本文中只随机列出一种。
| 描述 | 最大值 | 当前值 | 报警值 |
| 堆内存 | @Heap Configuration::MaxHeapSizesum(eden+servivor+old) | sum(eden+servivor+old) | 自设 |
| 非堆内存 | sum(perm+native) | 无 | |
| Eden | @Eden Space::capacity | @Eden Space::used | 无 |
| Survivor0 | @From Space::capacity | @From Space::used | 无 |
| Survivor1 | @To Space::capacity | @To Space::used | 无 |
| New gen(注意区别于) | @New Generation::capacityEden + 1 Survivor Space | @New Generation::used | 无 |
| Old gen | @concurrent mark-sweep generation::capacity(CMS是对old区的gc,所以此处即表示old gen) | @concurrent mark-sweep generation::capacity(CMS)::used | 自设 |
| Perm Gen | @Perm Generation::capacity | @Perm Generation::used | 自设 |
内存使用情况--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声明下方 |
| 类总数统计 | ?? |
内存使用情况—C heap
- top or ps aux
谁使用了内存
- Heapjmap –histojmap –dump ,then mat
- C heapgoogle perftools
GC的状况
| 描述 | 收集次数 | 收集时间 | 应用暂停时间 |
| Full GC | #FGC | #FGCT | 后在日志中查看 |
| Young GC | #YGC | #YGCT | 同上 |
-XX:+PrintGCDetails -XX:+PrintGCTimeStamps -XX:+PrintHeapAtGC -Xloggc:logs/gc.log
常用介绍:jinfo jmap jstack jstat
- 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。
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>
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
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
Usage: jstat -help|-options jstat -
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。。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。
| 统计class loader行为信息 | |
| 统计编译行为信息 | |
| 统计jdk gc时heap信息 | |
| 统计堆内存不同代的heap容量信息 | |
| 统计gc的情况（同-gcutil）和引起gc的事件 | |
| 统计gc时新生代的信息(相比gcutil更详细) | |
| 统计gc时新生代heap容量 | |
| 统计gc时，老年区的情况 | |
| 统计gc时，老年区heap容量 | |
| 统计gc时，permanent区heap容量 | |
| 统计gc时，heap情况 | |
| 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:+PrintComplation option. |
Java api方式监测
jre中提供了一些查看运行中的内部信息的api，这些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过这种方式访问这些信息。下面简单介绍一下这包括哪些信息，以及如何访问。
可以通过此api访问到运行中的jvm的类加载的信息、jit编译器的信息、内存分配的情况、线程的相关信息以及运行jvm的操作系统的信息。java.lang.management包中提供了9个接口来访问这些信息，使用ManagementFactory的静态get方法可以获得相应接口的实例，可以通过这些实例来获取你需要的相关信息。
更详细的关于MBean的介绍参见
demo1:查看一下当前运行的jvm中加载了多少个类。想详细了解如何使用这些api，可以参考java.lang.management包中的详细api文档。
public class ClassLoaderChecker { public static void main( String[] args ) throws Exception { ClassLoadingMXBean bean = ManagementFactory.getClassLoadingMXBean(); System.out.println( bean.getLoadedClassCount() ); } } demo2:自定义Mbean Type,记录的数据可通过jconsole等工具或自写代码查看, //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); }}相关推荐文章:
参考: