We used to be on systems where we seek for microsecond latencies, and if you recognize, a big garbage collection can last several milliseconds. These JVM options are used to enable the garbage collection logging, which is highly effective for the latency-sensitive operation. XX:-PrintGCTimeStamps - Print timestamps at garbage collection. XX:+PrintGCDetails - includes the data from -verbose:gc but also adds information about the size of the new generation and more accurate timings. Print GC -verbose:gc - logs garbage collector runs and how long they're taking. This option is particularly effective for a web server like Tomcat, which often loads classes of the web application during deployment.īy the way, It’s worth realizing that PermGen space is taken over by Metaspace in Java 8, and this option is not applicable if you are running with JRE 8 JVM. PermGen SizeĮarlier JVM options define the size of heap memory but -XX:PermSize is to define the size of PermGen space, where the string pool and class metadata is saved. You can have multiple caches, and you can specify the correct cache by adding a suboption to the -Xshareclasses option. The JVM connects to an existing cache or creates a cache if one does not exist. Specify Xshareclasses option to enable class data sharing in a shared class cache. XX:MinHeapFreeRatio – sets the minimum percentage of heap free after GC to avoid expansion to monitor the heap usage, you can use JCosole. XX:MaxHeapFreeRatio – sets the maximum percentage of heap free after GC to avoid shrinking. You will essentially always have -Xmsand -Xmx together. Xmx – This option is to define the maximum heap size of JVM, e.g., Xmx2048m which means the maximum heap size of JVM will be 2 GB only. Surprisingly yes! This is carried to prevent resizing during startup and enhance the startup time of JVM. So, when a JVM starts, the heap memory will be this much big. Xms – This option is to define starting heap size for JVM, e.g., Xms2048m which means an initial heap size of JVM is 2 GB around. Java heap size -Xms - set initial Java heap size If your argument is too long, then try using ps -auxww as this command will also show a long argument list as well.Īfter having a list of JVM flags, you can get an idea about the behaviors of any Java application, e.g., Tomcat. If more than one Java process is going on the system, then you may require to go with a keyword that is unique to your Java application. If the application is running on Linux, you can use ps -ef | grep java to identify the Java process and look at the JVM options printed as process arguments. Which JVM options are used by your application? Standard options don’t prepend anything to the option. Similarly, if you’re applying a non-standard option, you use -X. If you try an advanced option, you always use the option with -XX. Talking about JVM options, then there are three types of options that you can include to your JVM, standard, non-standard, and advanced options. If you are a Java developer or middleware administrator, then you should know what JVM options mean along with their importance, and how they impact your application. Import to know essential JVM (Java Virtual Machine) options for better performance and debugging. Src/main/java/org/exoplatform/jrebel/portlet/MyPortlet.java package Once created, you can add the source file for the portlet: Check Create a simple project (skip archetype selection).New Portlet Projectīefore going further with JRebel, you need to create a new portlet project: Simply follow the first 3 steps in this tutorial on the JRebel website. The first step is to install JRebel in Eclipse. To learn how to start eXo Platform in Eclipse, check out this tutorial. JRebel integrates well with Eclipse, which we used in the following example. In this tutorial, we will demonstrate how to use JRebel to speed up development with eXo Platform. JRebel is a tool that enables developers to instantly reload changes in Java sources files, without having to redeploy the application or restart the server.
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