A fundamental problem in automating object database storage reclamation is determining how often to perform garbage collection. We show that the choice of collection rate can have a significant impact on application performance and that the "best" rate depends on the dynamic behavior of the application, tempered by the particular performance goals of the user. We describe two semi-automatic, self-adaptive policies for controlling collection rate that we have developed to address the problem. Using trace-driven simulations, we evaluate the performance of the policies on a test database application that demonstrates two distinct reclustering behaviors. Our results show that the policies are effective at achieving user-specified levels of I/O operations and database garbage percentage. We also investigate the sensitivity of the policies over a range of object connectivities. The evaluation demonstrates that semi-automatic, self-adaptive policies are a practical means for flexibly controlling garbagecollection rate.
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