How to Resolve Out-of-Memory Errors in Apache Tomcat 6.0 Due to PermGen Space Exhaustion?

Permanent Generation (PermGen) Space Allocation in Tomcat 6.0

When working with Apache Tomcat 6.0, you may encounter an out-of-memory error originating from the permanent generation (PermGen) space during indexing operations. Understanding PermGen space management is crucial to resolving this issue.

Increasing PermGen Space

The space allocated to PermGen can be increased using the -XX:MaxPermSize flag. For instance, setting -XX:MaxPermSize=128m allocates 128 megabytes to PermGen. However, this approach only temporarily alleviates the problem.

Alternative Solutions

More efficient solutions involve enabling garbage collection for the PermGen and managing class unloading:

• -XX: UseConcMarkSweepGC: Enables concurrent mark-sweep garbage collection for PermGen.
• -XX: CMSPermGenSweepingEnabled: Allows the garbage collector to reclaim unused PermGen objects during concurrent collections.
• -XX: CMSClassUnloadingEnabled: Facilitates unloading of classes from the PermGen when no longer referenced.

Causes and Mitigation

PermGen space exhaustion typically occurs due to excessive redeployments. Monitoring PermGen usage with tools like virtualvm or jconsole can help determine if the space usage stabilizes after a warm-up period.

Alternative JVM Options

If PermGen space issues persist, consider switching to a different JVM implementation like the IBM JVM. Unlike other JVMs, the IBM JVM does not employ a PermGen, eliminating this potential performance bottleneck.

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