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Using Non-Standard (-XX) JVM Arguments

The Sun Java Virtual Machine contains non-standard HotSpot VM options that are used to improve virtual machine behavior, performance, and debugging. Non-standard options are prefixed with –XX.

Many non-standard options are available that can provide greater throughput and reduce overall latency. Use tuning exercises to determine which options are best suited for the conditions in your production environment. Use different logging options to provide insight into the value of each option. Given the variety of options and the chance that these options may change from release to release, Blackboard recommends testing them in your environments based on the output found in the garbage collections logs.

Some of these options are platform-specific and will not work across all certified Blackboard operating system platforms. In addition, these options can change across releases and patches, so pay close attention when using them.

The following table describes the options that will provide the majority of the performance gain.

Performance Gain Options
JVM Option Description
-XX:+UseConcMarkSweepGC The concurrent collector is used to collect the tenured generation and does most of the collection concurrently with the execution of the application. The application is paused for short periods during the collection.
-XX:+UseParNewGC This is used in conjunction with the concurrent collector on multiprocessor machines to enable young generation collection.
-XX:ParallelGCThreads This option should be set to the number of available CPUs for concurrent garbage collection. This option is to be used in conjunction with -XX:+UseParNewGC.
-XX:NewRatio This option sets the size ratio between young and old generational spaces. This is typically set to a value between 2 and 4 depending on garbage collection patterns.
-XX:NewSize, -XX:MaxNewSize This option sets the explicit size for the young generation space. This parameter requires explicit sizes, and is recommended in place of the -XX:NewRatio parameter for resizing the new generation space of the JVM.

To learn more about the JVM options supported by Java, see