Tuning JRE Heap Sizes

The amtune tool restarts the server to check its JVM mode and to determine how much heap size is available for setting OpenSSO cache and session entries. For other web containers, the amtune tool supports only 32-bit JRE. For other web containers, $WEB_CONTAINER and $CONTAINER_INSTANCE_DIR values are not required.

Although the amtune tool does not tune non-Sun web containers, it will tune OpenSSO parameters if $AMTUNE _TUNE_OPENSSO is set to true.

By default, the amtune tool runs based on the assumption that the following amount of memory (megabytes) is available for tuning OpenSSO when the web container (both Sun and non-Sun) is running with 32-bit JRE:

• (Sparc/x86/AIX) AMTUNE_MAX_MEMORY_TO_USE_IN_MB_SOLARIS=3584

• (Linux) AMTUNE_MAX_MEMORY_TO_USE_IN_MB_X86=2341

• (Windows) AMTUNE_MAX_MEMORY_TO_USE_IN_MB_DEFAULT=1536

The amtune tool also tunes OpenSSO Enterprise when it is deployed on WebSphere 6.1 and 7, and on AIX, although it does not tune IBM AIX system parameters or WebSphere container parameters.

For 64-bit JRE, the amtune tool limits the initial heap size (-Xms) to 12 GB for Web Server 7, and for Application Server 9.1 and GlassFish v2. If the Solaris operating system has at least twice as much virtual memory (swap space) as the desired initial JVM heap size, the initial heap size can be increased manually. There is no limit for the maximum heap size (-Xmx).

Using 64–bit JRE, the user session cache size and number of sessions are calculated by the amtune tool. The results can be many times more than those calculated for 32–bit JRE, depending upon available memory. Be sure to review these numbers and determine whether or not they are apropriate.