다운 받고 압축을 풀면, bin디렉토리가 있는데 visualvm.exe을 실행합니다. "I Accept" 클릭. 하면 아래와 같은 창이 나타납니다.
Local을 보시면 내 pc에 실행중인 java process에 대한 정보들이 보입니다. VisualVM을 더블클릭하시면 화면의 오른쪽에 해당 process에 대한 정보가 보입니다.
Eclipse를 한번 실행해봤습니다. 자동으로 java process가 등록이 되는군요.
Remote 서버의 java process를 모니터링 하는 방법에 대해서 알아보자. 왼쪽 메뉴에서 Remote를 선택하고 "Add Remote Host" 선택 후 Remote 서버 IP를 입력한다. 추가된 Remote host에서 마우스 우 클릭 후 "Add jstatd Connection" 선택.
Remote Host의 jstatd와 통신하기 위해서 "OK" 버튼 클릭. - "jstatd": A server that allows JVM monitoring tools like "jps" and "jstat" to access JVM processes from a remote machine. "jstatd" tool is distributed as part of the Sun JDK package and represented by the \Progra~1\java\jdk1.6.0_02\bin\jstatd.exe program file.
Remote Host의 jstatd를 설정하는 방법을 알아보자.
1. rmiregistry 실행하기 2. policy 파일 만들기 3. jstatd 실행하기
1. rmiregistry 실행하기 - The rmiregistry command starts a remote object registry on the specified port on the current host.
$JAVA_HOME/bin 으로 이동한다. [sroot@vpms bin]# ./rmiregistry 1099& [1] 32174 [sroot@vpms bin]#
2. policy 파일 만들기 - $JAVA_HOME/bin디렉토리에 jstatd.all.policy 파일을 생성하고 아래와 같이 입력한다.
- 실행 도중 아래와 같은 에러 발생함. - 해결방법은 jstatd.all.policy 파일이 제대로 되어 있는지 확인한다. - 저는 AllPermission에서 P를 소문자로 써서 발생함.
[sroot@vpms bin]# ./jstatd -J-Djava.security.policy=jstatd.all.policy -p 1099 Could not create remote object access denied (java.util.PropertyPermission java.rmi.server.ignoreSubClasses write) java.security.AccessControlException: access denied (java.util.PropertyPermission java.rmi.server.ignoreSubClasses write) at java.security.AccessControlContext.checkPermission(AccessControlContext.java:323) at java.security.AccessController.checkPermission(AccessController.java:546) at java.lang.SecurityManager.checkPermission(SecurityManager.java:532) at java.lang.System.setProperty(System.java:725) at sun.tools.jstatd.Jstatd.main(Jstatd.java:122) [sroot@vpms bin]#
모든 설정이 완료되면 아래 이미지와 같이 Remote Host에서 실행되는 java process 목록을 확인할 수 있다.
How Tomcat Interacts With The JVM Utilizing servlets allows the JVM to handle each request within a separate Java thread, as each servlet is in fact a standard Java class, with special elements that allow it to respond to HTTP requests. Tomcat's main function is to pass HTTP requests to the correct components to serve them, and return the dynamically generated results to the correct location after the JVM has processed them. If the JVM can't efficiently serve the requests Tomcat passes to it, Tomcat's performance will be negatively affected.
How to Configure Tomcat's Default JVM Preferences Once you decide on a JVM and install it on your server, configuring Tomcat to run on it is a very simple process. Simply edit catalina.sh, found in Tomcat's bin folder, and change the JAVA_HOME environment variable to the directory of your chosen JVM's JDK. When you restart Tomcat, it will be running on your new JVM.
Effective Memory Management The main thing to consider when tuning your JVM for Tomcat performance is how to avoid wasting memory and draining your server's power to process requests. Certain automatic JVM processes, such as garbage collection and memory reallocation, can chew through memory if they occur more frequently than necessary. You can make sure these processes only occur when they need to by using the JAVA_OPTS -Xmx and -Xms switches to control how JVM handles its heap memory. If your JVM is invoking garbage collection too frequently, use the -Xmx switch to start the JVM with a higher maximum heap memory. This will free up CPU time for the processes you really care about. To get even more out of this change, you can include the -Xms switch. This switch makes the JVM's initial heap memory size equal to the maximum allocated memory. This means the JVM will never have to reallocate more memory, a costly process that can eat up power you want being used to serve incoming requests. If your web applications can handle a lower garbage collection throughput, you can also experiment with the -Xincgc switch, which enables incremental garbage collection. This means that rather than halting in place to perform garbage collection tasks, the JVM will execute garbage collection in small phases. It can be tricky to determine the most balanced configuration for your site's needs. Fortunately, there's an easy way to capture data on how your JVM is handling garbage collection.Simply use the -verbose:gc switch to generate logs you can use to help you arrive at the best solution.
Configuring Threads Next, let's take a look at the way your JVM handles threads. There are two types of Java threads - green and native. Native threads are scheduled by your OS, while green threads are managed entirely within the user space of your Java Virtual Machine. If your JVM supports both, you should try both models to determine the best choice for your site. Generally, native threads offer the best performance, especially if you are running a lot of I/O bound applications (which is very likely, since you are running Tomcat). However, green threads outperform native threads in some specific areas, such as synchronization and thread activation. Try both and see which option gives you the biggest performance boost.
Managing Your JVM Tuning for performance is not a finite process. Usage situations change over time, and problems that are not immediately apparent can expose themselves over a longer period of time. There are a number of tools available to help you keep an eye on your JVM's performance. One of the most convenient solution is VisualVM, a tool that is packaged with the JDK, and can provide you with great performance statistics. Other commonly used JVM monitoring tools included with the SDK include console, jps, and jstack. Run regular tests on your JVM to make sure its configuration still suits your needs, and you can be sure that your Tomcat instances will always perform at their best!
