Providing persistence on small machines

The aim of our research is to investigate the feasibility of running an orthogonally persistent Java(TM) on a "small" machine; a platform with limited memory and possibly not even having access to a local disk. The implementation is designed to interface with the PJSL store being developed for the PJama project. The paper discusses the modification of a lightweight Java Virtual Machine (JVM) in order to provide persistence. It highlights decisions that were made in the areas of memory management, object faulting and update tracking in order to implement these facilities efficiently without using undue amounts of memory. Also discussed are the problems of caching and of swapping reachable objects to the persistent store in order to make more memory available. It is possible to configure the machine to use different strategies for each of these mechanisms so that comparisions can be made. Applications such as Generalised Search Tree (GiST) indexing of data collections have been run on the machine, and the performance of different machine configurations has been measured. The paper first gives a brief description of the original lightweight JVM before showing how persistence mechanisms were incorporated. We conclude with some results from our ongoing evaluation of alternative configurations.