Tuning Java Virtual Machine Settings

You can use the JAVA_ARGS environment variable to provide global configuration arguments that can be passed to the JVM, or you can use the java.properties file. Any argument that can be used with the java command can be used with both methods.

For more information, see dsjavaproperties in Oracle Fusion Middleware Command-Line Usage Guide for Oracle Unified Directory.

For additional information about tuning the JVM, see the Java Performance Documentation. The Java Tuning White Paper and the Garbage Collection Tuning documents are particularly useful.

The main JVM tunable options include the following:

-server

Always use the server JVM instead of the client JVM. The client VM is better optimized for processes that run for a short period of time and need to start as quickly as possible. The server VM can take longer to warm up but is faster in the long run.

-d32 or -d64

Select the 32-bit or 64-bit version of the JVM (if applicable for the underlying system). Use the 64–bit JVM if you require a heap greater than 4 Gbytes.

-XX:+UseCompressedOops

Use this option if you use the 64–bit JVM and if the heap size is less than 32 Gbytes.

-Xms2g and -Xmx2g

This parameter sets the initial and maximum heap size available to the JVM. Increasing the heap size can improve performance, but setting it too high can have a detrimental effect in the form of longer pauses for full garbage collection runs. The initial and maximum sizes should generally be set to the same values.

For maximum performance, size the heap so that the entire DB can be cached in memory. In general, you should allocate enough heap for the server runtime and the rest to the DB cache.

-XX:NewSize=512M

The total heap space is divided into the old generation and the young generation. This parameter sets the size of the young generation. The remaining memory (old generation) must be sufficient to hold the DB cache plus some overhead.

-XX:+UseConcMarkSweepGC

Use the Concurrent Mark Sweep (CMS) garbage collector. This option allows the JVM to minimize the response time of LDAP operations, but it can have a small impact on the overall performance (throughput) of the server. Use this option of long pause times are not tolerated.

Additional JVM arguments that are related to performance and scalability include the following:

-XX:CMSInitiatingOccupancyFraction=<percentage>

Specify the level at which the CMS garbage collection is started. The default value is approximately 68%. Use this value if you want to set the percentage to something other than the default value.

-XX:+UseBiasedLocking

Improve locking performance in the server in cases where there is not expected to be a high degree of contention.

-XX:LargePageSizeInBytes=256m

Use large pages for the information it stores in memory. This argument applies primarily to systems using the UltraSPARC T1 processor.

-XX:+UseParallelGC

Specify that the system should use parallel garbage collection, which is particularly useful on systems with a large number of CPUs.

-XX:+UseParallelOldGC

Specify that the JVM should use parallel garbage collection for the old (tenured) generation.

-XX:ParallelGCThreads=8

Specify that the JVM should use 8 threads when performing parallel garbage collection. The default is to use a number of threads equal to the number of CPUs, but this can be inappropriate on systems with a very large number of CPUs or on CMT-based systems like those using the UltraSPARC T1 processor.