AggressiveHeap - Server Performance Option

The -XX:+AggresiveHeap option inspects the machine resources (size of memory and number of processors) and attempts to set various parameters to be optimal for long-running, memory allocation-intensive jobs. It was originally intended for machines with large amounts of memory and a large number of CPUs, but in the J2SE platform, version 1.4.1 and later it has shown itself to be useful even on four processor machines. The physical memory on the machines must be at least 256MB before AggresiveHeap can be used. The size of the initial heap is calculated based on the size of the physical memory and attempts to make maximal use of the physical memory for the heap (i.e., the algorithm attempts to use half of available memory, or all of possible memory less 160mb, whatever is the lesser of the two).

There are several optimizations and changes in parameter values with AggressiveHeap in J2SE platform version 1.4.2 that were added in an effort to make the option more useful for general server use. AggressiveHeap is recommended for server applications requiring high performance and scalability and can greatly ease performance tuning efforts. With Sun's emphasis on low-cost enterprise computing, we renewed our commitment to performance on Sun's latest offerings. Illustration 1 shows the performance gains as measured on SPECjbb?2000 while using AggressiveHeap on J2SE platform version 1.4.1 and J2SE version 1.4.2. Although SPARC was already highly optimized in J2SE version 1.4.1 with AggressiveHeap, we made further improvements of nearly 20% in J2SE version 1.4.2.

Illustration 1: J2SE platform version 1.4.2 Performance as shown with SPECjbb2000