Generational Garbage Collection with IBM JVM for Oracle Unified Directory

A main difference between IBM J9 JVM and Oracle JVM is that IBM’s JVM has different heap structure than Oracle’s JVM. By default IBM JVM (java 6) does not use Generational Garbage Collector. Such setting has adverse effects on OUD as OUD allocates a huge numbers of transient objects. Using the default IBM JVM settings lead to full garbage collections that freezes the directory services.


I recommend to use generational heap structure systematically with OUD. This can be enabled by the JVM option

OUD 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/ 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. More about JVM param settings at

To use the gencon garbage collector policy for a specific OUD instance, do the following:

Edit the file located at instance-dir/OUD/config/
Add -Xgcpolicy:gencon at the end of the line starting with start-ds
Run instance-dir/OUD/bin/dsjavaproperties
Restart the OUD instance


2 thoughts on “Generational Garbage Collection with IBM JVM for Oracle Unified Directory

  1. Sachin Dave

    Dear Expert,

    We have tried to implement suggest configuration in your article on our IBM JRE 7 Release 1 with OUD 11gR2PS3 but it is not working.

    When we tries to start directory server after setting –Xgcpolicy:gencon it is failing and complaining about compatible JRE version.

    Any ideas why this is happening ?


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