Supporting method migration in a distributed object database system: a performance study

We describe the model and implementation of two approaches for method execution in distributed object query processing. The first approach is the traditional data migration approach in which remote data accesses (if required) are made to compose an in-memory object at the query site which is followed by method invocation on this object. The second approach of method migration allows the method execution to be migrated to a remote site where object data is locally available, or it can accessed with little cost. We present the results of our experimental studies. We use the O-Raid distributed database system in our experiments. We demonstrate how the performance of query processing can be improved using the method migration approach for method invocations on large and complex objects. Our results are applicable for operations on large distributed multimedia objects. We develop a benchmark for dynamic method execution in queries and perform measurements. The overheads in method execution using both the data migration and method migration approaches are identified and analyzed. Different network environments such as local area network (LAN), metropolitan area network (MAN), and wide area network (WAN) are considered in our experimental study. A wide area network emulator (WANCE) tool, also developed at Purdue University, is integrated with O-Raid system for emulating Internet sites in our laboratory environment. We analyze the impact of communication latencies between the distributed sites on the relative performance of these method execution strategies.