7.11.1 How to estimate the memory size of Explicit heap (Estimating memory size used in J2EE server)
The settings to use the Explicit Memory Management functionality are required as a prerequisite for tuning Explicit heap. The Explicit Memory Management functionality is enabled when -XX:+HitachiUseExplicitMemory is specified as the start option of JavaVM. In J2EE servers, there are default settings to use the Explicit Memory Management functionality. Also, the objects responsible for increasing the memory size of the Tenured area are set to be allocated in Explicit heap. Therefore, always estimate the memory size of Explicit heap required for the objects allocated by J2EE servers.
If the memory size of Explicit heap is not estimated properly, the Explicit Memory Management functionality is not effective.
In a J2EE server, objects related to the HTTP session that cause the memory size of the Tenured area to increase are deployed in the Explicit heap.
As a result of estimating the memory size of the Explicit heap, if the memory size of the Explicit heap used by the HTTP session-related objects is extremely large, see Appendix A Efficient Usage of the Explicit Heap Used in an HTTP session to revise the application design.