Investigating the effects of using different nursery sizing policies on performance

In this paper, we investigate the effects of using three different nursery sizing policies on overall and garbage collection performances. As part of our investigation, we modify the parallel generational collector in HotSpot to support a fixed ratio policy and heap availability policy (similar to that used in Appel collectors), in addition to its GC Ergonomics policy. We then compare the performances of 16 large and small multithreaded Java benchmarks; each is given a reasonably sized heap and utilizes all three policies. The result of our investigation indicates that many benchmarks are sensitive to heap sizing policies, resulting in overall performance differences that can range from 1 percent to 36 percents. We also find that in our server application benchmarks, more than one policy may be needed. As a preliminary study, we introduce a hybrid policy that uses one policy when the heap space is plentiful to yield optimal performance and then switches to a different policy to improve survivability and yield more graceful performance degradation under heavy memory pressure.