Setting the JVM Heap Size for OC4J Processes

If you have sufficient memory available on your system and your application is memory intensive, you can improve your application performance by increasing the JVM heap size from the default value. While the amount of heap size required varies based on the application and on the amount of memory available, for most OC4J server applications, a heap size of at least 256 Megabytes is advised. If you have sufficient memory, using a heap size of 512 Megabytes or larger is preferable.

To change the size of the heap allocated to the OC4J processes in an OC4J instance, use the procedures outlined in "Using Application Server Control Console to Change JVM Command Line Options", and specify the following Java options:

-Xmssizem -Xmxsizem

Where size is the desired Java heap size in megabytes.

If you know that your application will consistently require a larger amount of heap, you can improve performance by setting the minimum heap size equal to the maximum heap size, by setting the JVM -Xms size to be the same as the -Xmx size.

For example, to specify a heap size of 512 megabytes, specify the following:

-Xms512m -Xmx512m

You should set your maximum Java heap size so that the total memory consumed by all of the JVMs running on the system does not exceed the memory capacity of your system. If you select a value for the Java heap size that is too large for your hardware configuration, one or more of the OC4J processes within the OC4J instance may not start, and Oracle Enterprise Manager 10g Application Server Control Console reports an error. Review the log files for the OC4J instance in the directory $ORACLE_HOME/opmn/logs, to find the error report:

Could not reserve enough space for object heap
Error occurred during initialization of VM

If you select a value for the JVM heap size that is too small, none of the OC4J processes will be able to start, and, after a timeout while attempting to make the change, Application Server Control Console reports an error, "An error occurred while restarting..." In this case, if you review the log files for the OC4J instance in the directory $ORACLE_HOME/opmn/logs, you may find errors similar to the following:

java.lang.OutOfMemoryError