Uk Hyun Lee, Bu Hyun Hwang

The KIPS Transactions:PartD, Vol. 9, No. 2, pp. 185-194, Apr. 2002
10.3745/KIPSTD.2002.9.2.185,   PDF Download:

Abstract

Most of mobile computing systems allow mostly read-only transactions from mobile clients for retrieving various types of information such as stock data, traffic information and news updates. Since previous concurrency control protocols, however, do not consider such a particular characteristics, the performance degradation occurs when previous schemes are applied to the broadcast environment. In this paper, we propose OCC/UTF(Optimistic Concurrency Control with Update Transaction First) that is most appropriate for broadcast environment. OCC/UTF lets a query transaction, that has already read the data item which was invalidated by update transaction, read again the same data item without the abort of the query transaction due to non-serializability. Therefore, serializable order is maintained and the query transaction is committed safely regardless of commitment of update transactions. In OCC/UTF, Clients need not require server to commit their query transactions. Because of broadcasting the validation reports including values updated recently to clients, it reduces the overhead of requesting recent values from the server and the server need not also re-broadcast the newest values. As a result, OCC/UTF makes full use of the asymmetric bandwidth. It can also improve transaction throughput by increasing the commit ratio of query transactions as much as possible.

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