Use this page to view and change the Java virtual machine (JVM) configuration settings of a process for an application server.
To view this administrative console page, connect to the administrative console and navigate to the Java virtual machine panel:
Application server | Servers > Application Servers > server1. Then, under Server Infrastructure, click Java and Process Management > Process Definition > Java Virtual Machine |
Deployment manager | System Administration > Deployment Manager. Then, under Server Infrastructure, click Java and Process Management > Process Definition > Java Virtual Machine |
Node agent | System Administration > Node Agent > nodeagent. Then, under Server Infrastructure, click Java and Process Management > Process Definition > Java Virtual Machine |
Specifies whether to use verbose debug output for garbage collection. The default is not to enable verbose garbage collection.
Data type | Boolean |
Default | false |
When this field is enabled, a report is written to the output stream each time the garbage collector runs. This report should give you an idea of what is going on with Java garbage collection.
83.29/3724.32 * 100 = 2.236%
If you are spending more than 5% of your time in GC and if GC is occurring frequently, you may need to increase your Java heap size.
To determine this, look at the %free. You want to make sure the number is not continuing to decline. If the %free continues to decline you are experiencing a gradual growth in allocated heap from GC to GC which could indicate that your application has a memory leak.
Specifies whether to use verbose debug output for native method invocation. The default is not to enable verbose Java Native Interface (JNI) activity.
Data type | Boolean |
Default | false |
Specifies whether to use HProf profiler support. To use another profiler, specify the custom profiler settings using the HProf Arguments setting. The default is not to enable HProf profiler support.
This setting only applies to the base WebSphere Application Server and the WebSphere Application Server - Express products.
If you set the Run HProf property to true, then you must specify command-line profiler arguments as values for the HProf Arguments property.
Data type | Boolean |
Default | false |
Specifies command-line profiler arguments to pass to the JVM code that starts the application server process. You can specify arguments when HProf profiler support is enabled.
This setting only applies to the base WebSphere Application Server and the WebSphere Application Server - Express products.
HProf arguments are only required if the Run HProf property is set to true.
Data type | String |
Specifies whether to run the JVM in debug mode. The default is not to enable debug mode support.
If you set the Debug Mode property to true, then you must specify command-line debug arguments as values for the Debug Arguments property.
Data type | Boolean |
Default | false |
Specifies command-line debug arguments to pass to the JVM code that starts the application server process. You can specify arguments when Debug Mode is enabled.
For WebSphere Application Server Network Deployment configurations, Debug arguments are only required if the Debug Mode property is set to true. If you enable debugging on multiple application servers on the same node, make sure that the servers are using different address arguments, which define the port for debugging. For example, if you enable debugging on two servers and leave the default debug port for each server as address=7777, the servers could fail to start properly.
Data type | String |
Units | Java command-line arguments |
Specifies command line arguments to pass to the Java virtual machine code that starts the application server process.
You can use -Xquickstart for initial compilation at a lower optimization level than in default mode. Later, depending on sampling results, you can recompile to the level of the initial compile in default mode. Use -Xquickstart for applications where early moderate speed is more important than long run throughput. In some debug scenarios, test harnesses and short-running tools, you can improve startup time between 15-20%.
You can use -Xverify:none if you want to skip the class verification stage during class loading . Using -Xverify:none with the just in time (JIT) compiler enabled, improves startup time by 10-15%.
You can use -Xnoclassgc to disable class garbage collection. This action leads to more class reuse and slightly improved performance. The trade-off is that you won't be collecting the resources owned by these classes. You can monitor garbage collection using the verbose:gc configuration setting, which will output class garbage collection statistics. Examining these statistics will help you understand the trade-off between the reclaimed resources and the amount of garbage collection required to reclaim the resources. However, if the same set of classes are garbage collected repeatedly in your workload, you should disable garbage collection. Class garbage collection is enabled by default.
You can use several garbage collection threads at one time, also known as parallel garbage collection. When entering this value in the Generic JVM arguments field, also enter the number of processors that your machine has, for example, -Xgcthreadsn, where n is the number of processors. On a node with n processors, the default number of threads is n. You should use parallel garbage collection if your machine has more than one processor. This argument is valid only for the IBM Developer Kit.
You can use -Xnocompactgc to disable heap compaction, which is the most expensive garbage collection operation. Avoid compaction in the IBM Developer Kit. If you disable heap compaction, you eliminate all associated overhead.
You can use -Xinitsh to set the initial heap size where class objects are stored. The method definitions and static fields are also stored with the class objects. Although the system heap size has no upper bound, set the initial size so that you do not incur the cost of expanding the system heap size, which involves calls to the operating system memory manager. You can compute a good initial system heap size by knowing the number of classes loaded in the WebSphere Application Server product, which is about 8,000 classes, and their average size. Having knowledge of the applications helps you include them in the calculation. You can use this argument only with the IBM Developer Kit.
You can use -Xgpolicy to set the garbage collection policy. If the garbage collection policy (gcpolicy) is set to optavgpause, concurrent marking is used to track application threads starting from the stack before the heap becomes full. The garbage collector pauses become uniform and long pauses are not apparent. The trade-off is reduced throughput because threads might have to do extra work. The default, recommended value is optthruput. Enter the value as -Xgcpolicy:[optthruput|optavgpause]. You can use this argument only with the IBM Developer Kit.
The Sun-based Java Development Kit (JDK) Version 1.4.2 has generation garbage collection, which allows separate memory pools to contain objects with different ages. The garbage collection cycle collects the objects independently from one another depending on age. With additional parameters, you can set the size of the memory pools individually. To achieve better performance, set the size of the pool containing short lived objects so that objects in the pool do not live through more then one garbage collection cycle. The size of new generation pool is determined by the NewSize and MaxNewSize parameters.
-XX:NewSize (lower bound) -XX:MaxNewSize (upper bound) -XX:SurvivorRatio=NewRatioSize
The default values are:NewSize=2m MaxNewSize=32m SurvivorRatio=2. However, if you have a JVM with more than 1GB heap size, you should use the values: -XX:newSize=640m -XX:MaxNewSize=640m -XX:SurvivorRatio=16, or set 50 to 60% of total heap size to a new generation pool.
You can use -Xminf to specify the minimum free heap size percentage. The heap grows if the free space is below the specified amount. In reset enabled mode, this option specifies the minimum percentage of free space for the middleware and transient heaps. This is a floating point number, 0 through 1. The default is .3 (30%).
Java HotSpot Technology in the Sun-based Java Development Kit (JDK) Version 1.4.2 introduces an adaptive JVM containing algorithms for optimizing byte code execution over time. The JVM runs in two modes, -server and -client. If you use the default -client mode, there will be a faster startup time and a smaller memory footprint, but lower extended performance. You can enhance performance by using -server mode if a sufficient amount of time is allowed for the HotSpot JVM to warm up by performing continuous execution of byte code. In most cases, use -server mode, which produces more efficient run-time execution over extended periods. You can monitor the process size and the server startup time to check the difference between -client and -server.
Data type | String |
Units | Java command line arguments |
Specifies a full path name for an executable JAR file that the JVM code uses.
Data type | String |
Units | Path name |
Specifies whether to disable the just in time (JIT) compiler option of the JVM code.
If you disable the JIT compiler, throughput decreases noticeably. Therefore, for performance reasons, keep JIT enabled.
Data type | Boolean |
Default | false (JIT enabled) |
Recommended | JIT enabled |
Specifies JVM settings for a given operating system.
For the Network Deployment product, when the process starts, the process uses the JVM settings for the node as the JVM settings for the operating system.
Data type | String |
Specifies whether to use verbose debug output for garbage collection. The default is not to enable verbose garbage collection.
Data type | Boolean |
Default | false |
When this field is enabled, a report is written to the output stream each time the garbage collector runs. This report should give you an idea of what is going on with Java garbage collection.
83.29/3724.32 * 100 = 2.236%
If you are spending more than 5% of your time in GC and if GC is occurring frequently, you may need to increase your Java heap size.
To determine this, look at the %free. You want to make sure the number is not continuing to decline. If the %free continues to decline you are experiencing a gradual growth in allocated heap from GC to GC which could indicate that your application has a memory leak.