Configuring the Default JVM and Java Arguments
- The Java Properties File Format
- Configuring JVM Options
To Specify the JAVA_HOME Environment Variable for a Specific Utility
To Specify the Java Arguments for a Specific Utility

Configuring the Default JVM and Java Arguments

The directory server provides a means of configuring the Java Virtual Machine (JVM) and Java options for each command-line utility and for the directory server itself. The Java configuration is provided in a properties file, located at instance-dir/OUD/config/java.properties. The configuration specified in this file is taken into account each time the dsjavaproperties command is run. If you do not run the dsjavaproperties command, the properties file is ignored.
The properties file can be used to specify (among other arguments) whether a command runs using the JVM in -server mode or -client mode. By default, all client applications run in -client mode, while the directory server and certain server utilities run in -server mode. Generally, -server mode provides higher throughput than -client mode, at the expense of slightly longer startup times.
For certain commands (import-ldif, export-ldif, backup, and restore) you can also specify different Java arguments (and a different JVM) depending on whether the command is run in online or offline mode.

The Java Properties File Format

The Java properties file has the following format.

command-name.java-home=JVM-path
command-name.java-args=JVM-arguments

The following table shows three properties present in the java.properties file that are of particular importance.

	Property	Description
overwrite-env-java-args	If True, the system checks the default.java-args property in this properties file before the checking the OPENDS_JAVA_ARGS environment variable. If false, the system checks the OPENDS_JAVA_ARGS environment variable first.
default.java-home	Sets the JVM that will be used for the directory server and for all of its command-line utilities, unless a different JVM is specified for a particular utility.

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Configuring JVM Options

The following table summarizes the Java options that can have an impact on server performance. Note that some of these options apply only to the Sun JVM.

	Condition	Option
	-server	Selects server application runtime optimizations. The directory server will take longer to start and “warm up” but will be more aggressively optimized to produce higher throughput.
	-d64	For 64-bit machines only. By default, the directory server selects a 32-bit JVM regardless of the architecture. This options should be specified when a large JVM heap is required (greater than 4 Gytes) and the architecture is 64-bit.
	-Xms2G -Xmx2G	Selects the initial and maximum memory sizes available to the JVM, respectively. These values are used for the JVM heap, which reserves memory for the directory server and its database (DB) cache (or caches if more than one). Increasing the amount of memory available can improve performance, but increasing it to too high a value can have a detrimental effect in the form of longer pauses for full garbage collection runs. Therefore, the initial and maximum sizes should be set to the same value. As a general guideline, take a look at the size of the Oracle Berkeley Java Edition (JE) database folders (instance-dir/OUD/db/userRoot). Based on the folders’ combined size, determine how much memory you want to reserve for the DB cache. After determining this value, tune the local DB back-end properties, db-cache-percent or db-cache-size and other JVM options appropriately. Be careful to allow additional memory for the server runtime. For example, if you have a single database of 1 Gbyte, which you want to store entirely in memory, then a 2 Gbyte heap with 60% reserved for the DB cache should be sufficient for efficient directory server performance. You can test this setup by preloading the database with the local database back end by using the preload-time-limit property. JVM heaps greater than 4 Gbytes require a 64-bit JVM.
	DisableExplicitGC	Prevents external applications from forcing expensive garbage collections. If you are using jstatd or other RMI-based applications to monitor Oracle Unified Directory, you should consider using this option in order to avoid unexpected pauses.
	-XX:NewSize=512M	In heavy throughput environments, you should consider using this option to increase the size of the JVM young generation. By default, the young generation is quite small, and high throughput scenarios can result in a large amount of generated garbage. This garbage collection, in turn, causes the JVM to inadvertently promote short-lived objects into the old generation.
Server Only	-XX:+UseConcMarkSweepGC	Selects the CMS garbage collector. This garbage collector is set for low pause time. It will result in a Java application that has a lower average throughput, but much shorter CPU-intensive garbage collections. This option is required in environments that have response time constraints.
	-XX:CMSInitiatingOccupancyFraction=70	Selects the level at which the collection is started. The default value is 68%.
Offline Import Only	-XX:+UseParallelOldGC	Selects the parallel old generational garbage collector. This garbage collector is set for high throughput. It will maximize the average throughput of the import-ldif utility at the cost of an occasional stop-the-world garbage collection, which is not as critical to imports.
	-XX:+PrintGCDetails	Prints the garbage collection details.
	-XX:+PrintGCTimeStamps	Prints the garbage collection time stamps to help with debugging.
Other Applications (for example, dsconfig)	-client	Selects client application run-time optimizations. The application will be faster to start and more responsive due to lower compilation overheads.
	-Xms8m	Selects a low initial JVM heap size for an application.

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To Specify the JAVA_HOME Environment Variable for a Specific Utility

Edit the Java properties file as follows: command-name.java-home=jvm.For example, to specify a particular JDK 1.6 for the offline import, edit the line that starts with import-ldif.offline in the java.properties file, as follows: import-ldif.offline.java-home=/usr/jdk1.6.
Run the dsjavaproperties command to apply the property.

To Specify the Java Arguments for a Specific Utility

Edit the Java properties file as follows: command-name.java-args=arguments.For example, to specify that a maximum heap size of 256 Mbytes be used for the online export, edit the line that starts with export-ldif.online in the java.properties file, as follows: export-ldif.online.java-args=-Xms256m -Xmx256m.