Main-Memory Management to support Orthogonal Persistence for Java

The main-memory management of an object cache that provides an orthogonally persistent platform for Java is described. Features of the architecture include: two levels of bu ering between the disk and virtual machine, a consistent representation of transient and active objects, an e cient residency checking algorithm in the presence of multiple threads of execution, and well developed object-cache management technology. We present some of the challenges of providing persistence for the Java virtual machine, which may be typical of any attempt at an industrial-strength orthogonally persistent programming system. Some of these might have been avoided by sacri cing persistence independence, but that is far too valuable to sacri ce. We report on some detailed investigations of pinning and cache replacement techniques applicable in this context. The information available for eviction-victim selection is inevitably limited by imprecise information about the state of the machine and the cost of collection. The question is raised whether we can do better than random eviction with real rather than synthetic loads given these limits.