Implementing Causal Logging Using OrbixWeb Interception

Some form of replicated data management is a basic service of nearly all distributed systems. Replicated data management maintains the consistency of replicated data. In wide-area distributed systems, causal consistency is often used, because it is strong enough to allow one to easily solve many problems while still keeping the cost low even with the large variance in latency that one finds in a wide-area network. Causal logging is a useful technique for implementing causal consistency because it greatly reduces the latency in reading causally consistent data by piggybacking updates on existing network traffic.

We have implemented a CORBA service, called COPE, that is implemented by using causal logging. COPE also shares features with some CORBA security services and is naturally implemented using the OrbixWeb interception facilities. In implementing COPE in OrbixWeb, we encountered several problems. We discuss COPE, its implementation in OrbixWeb, and the problems we encountered in this paper. We hope that this discussion will be of interest to both those who are implementing and who are planning on using CORBA interception facilities.