3 Runtime

This chapter describes important options that control the runtime behavior of the HotSpot VM.

Runtime Options

Note:

Some of the tools described in this document require a commercial license for use in production. To learn more about commercial features and how to enable them, see http://www.oracle.com/technetwork/java/javaseproducts/.

Runtime Options

The following table lists some important equivalent options of the runtime subsystem in Oracle JRockit and HotSpot.

Table 3-1 Runtime Options

Oracle JRockit	HotSpot	Note
`-XX:+UseLazyUnlocking`	`-XX:+UseBiasedLocking`	`UseBiasedLocking` improves the performance of uncontended synchronization. This option is enabled by default. However If the application has high contended synchronization, then disabling `UseBiasedLocking` benefits the performance.
`-XlargePages`	`-XX:+UseLargePages`	In HotSpot VM, this option is ON by default on Solaris. On Linux, this has been disabled since 7u60 and 8. Use `-XX:+UseLargePages` to enable the use of large pages on the platforms where it is disabled by default. It must be noted that `-XX:+UseLargePages` does not enable the use of large pages in the MetaSpace. To enable this option, add `-XX:+UseLargePagesInMetaspace`.
`-XX:MaxLargePageSize`	`-XX:LargePageSizeInBytes=size`	Sets the maximum size (in bytes) for large pages used for Java heap. By default, the size is set to 0, meaning that the JVM chooses the size for large pages automatically.
`-XXcompressedRefs`	`-XX:+UseCompressedOops`	Use of compressed oops is the default for 64-bit HotSpot JVM processes when `-Xmx` is not specified and for values of `-Xmx` less than 32 gigabytes.