SDI Seminar

Speaker: Krithi Ramamritham, University of Massachusetts-Amherst

Date: April 23, 1999
Time: 2:00 pm
Place: Wean Hall 8220

Reading Consistent and Current Data "Off the Air"


A crucial consideration in environments where data is broadcast to clients is the low bandwidth available for clients to communicate with servers. Many applications in such environments need to read data that is mutually consistent as well as current. However, given the asymmetric communication capabilities and the needs of clients in mobile environments, traditional serializability-based approaches are too restrictive, unnecessary, and impractical. We thus propose the use of a weaker correctness criterion called update consistency and outline a suite of mechanisms based on this criterion that ensure (1) the "mutual consistency" of data maintained by the server and read by clients, and (2) the "currency" of data read by clients. Using these mechanisms, clients can obtain data that is current and mutually consistent "off the air", i.e., without contacting the server to, say, obtain locks. Experimental results show a substantial reduction in response times as compared to existing (serializability-based) approaches. A further attractive feature of the approach is that if caching is possible at a client, weaker forms of currency can be obtained while still satisfying the mutual consistency of data.


Krithi Ramamritham received the Ph.D. in Computer Science from the University of Utah. Currently he is a Professor at the University of Massachusetts and holds a visiting position at the Indian Institute of Technology, Bombay. Ramamritham's interests span the areas of real-time systems, transaction support in advanced database applications, and real-time databases systems. A Fellow of the IEEE, he has served as Program Chair and General Chair for the Real-Time Systems Symposium in 1994 and 1995 respectively. He serves on the editorial board of many journals, including the IEEE Transactions on Parallel and Distributed Systems and the Real-Time Systems Journal. He has co-authored two IEEE tutorial texts on real-time systems, a text on advances in database transaction processing, and a text on scheduling in real-time systems.