When using the "+XX:+UseISM" parameter, the user no longer has control of how large the allocation of the heap is. When we attempted to use this parameter at Sun's recommendation, the JVM core dumped immediately (April 2001). We reported the problem to the Sun representative who asked us to use it and also to the Java Service group. We received numerous "we're working on it" notes, then a long period of silence. As of about 8 months later (Jan 2002), we were informed that this would be fixed in Version 1.4.0 which is to be released "shortly".

The net of the core dump is this: This pair of options is designed to grab as much memory as it can for the heap, and then lock it down. It seems, this was only tested on machine with a memory size larger than my 4GB. There are no Sun SPECjbb2000 disclosures where this ISM parameter is used where the real memory of the system is less than 16GB of real memory.

The information below will show that the reason the JVM code is failing on our system is that the "+XX:+UseISM" parameter used with the "+XX:+AggressiveHeap" is trying to allocate more memory than the system has to allocate. Hence, an immediate core dump.

Our belief is that this pair of options was specially formulated and only intended for high performance benchmarking. Your "actual performance" may be lower, as the saying goes.