Chapter 4. JVM tuning

You must set an appropriate heap size to prevent out of memory errors.

The -Xms option sets the initial heap size, and -Xmx sets the maximum heap size. It is recommended for production environments that you set the initial and maximum heap size options to the same size, so that the heap size is fixed and pre-allocated.

For example, the following options set a 2048 MB heap size:

-Xms2048M -Xmx2048M

-Xms2048M -Xmx2048M

It is recommended that you test your applications under load in a development environment to determine the maximum memory usage. Your production heap size should be at least 25% higher than the tested maximum to allow room for overhead.

Although the parallel garbage collector, also known as the throughput garbage collector, is the default garbage collector in Java 8 for server-class machines, Red Hat recommends using the G1 garbage collector, which is expected to be the default from Java 9 onward. The G1 garbage collector generally performs better than the CMS and parallel garbage collectors in most scenarios.

To enable the G1 collector, use the following JVM option:

-XX:+UseG1GC

-XX:+UseG1GC

Enabling large pages for JBoss EAP JVMs results in pages that are locked in memory and cannot be swapped to disk like regular memory.

Especially for memory-intensive applications, the advantage of using large pages is that the heap cannot be paged or swapped to disk, and is thus always readily available.

One disadvantage of using large pages is that other processes running on the system might not have quick access to memory, which might result in excessive paging for these processes.

As with any other performance configuration change, it is recommended that you test the impact of the change in a testing environment.

For more information, see the Oracle documentation on Java support for large pages.

For Red Hat Enterprise Linux and Solaris platforms, you must configure appropriate ulimit values for JBoss EAP JVM processes. The "soft" ulimit can be temporarily exceeded, while the "hard" ulimit is the strict ceiling for the usage of a resource. Appropriate ulimit values vary depending on your environment and applications.

If the limits applied to JBoss EAP processes are too low, you will see a warning like the following when starting JBoss EAP:

WARN  [org.jboss.as.warn.fd-limit] (main) WFLYSRV0071: The operating system has limited the number of open files to 1024 for this process; a value of at least 4096 is recommended.

WARN  [org.jboss.as.warn.fd-limit] (main) WFLYSRV0071: The operating system has limited the number of open files to 1024 for this process; a value of at least 4096 is recommended.

To see your current ulimit values, use the following commands:

To set the ulimit for the maximum number of open files, use the following commands with the number you want to apply:

JBoss EAP managed domain hosts have separate JVMs for the host controller and process controller.

You can tune the host controller and process controller JVM settings, but even for large managed domain environments, the default JVM configuration for the host controller and process controller should suffice.

The default configurations for host controller and process controller JVMs have been tested with a managed domain size of up to 20 JBoss EAP hosts each running 10 JBoss EAP servers, for a total domain size of 200 JBoss EAP servers.

If you experience issues with larger managed domains, you might need to monitor the host controller or process controller JVMs in your environment to determine appropriate values for JVM options such as heap size.