Processing mobile read-only transactions in broadcast environments with group consistency

Abstract

In broadcast environments, maintaining global serializability for all transactions at mobile clients and database server is expensive and inefficient. On the one hand, not all mobile commerce applications require such a high degree of data consistency as the serializability. On the other hand, the mechanism of concurrency control protocols designed for conventional database systems needs a significant amount of bandwidth for bi-directional message passing. This kind of message passing is not desirable in broadcast environments where communication between mobile clients and the server is asymmetric. In this research, we propose separate algorithms to process mobile read-only transactions (MROTs) locally at mobile client side. Firstly, a family of No-Read-Set (NRS) Algorithms is devised to process MROTs for different consistency requirements with respect to update transactions executing concurrently at the server. Further, the NRS-Algorithms are extended to ensure consistency in a group of MROTs. Group view consistency allows a group of MROTs to perceive the same consistent view produced by update transactions at the server. Group strong consistency allows only serializable schedules as required by the serializability. Finally, a group consistency model is introduced to support different consistency requirements within a group and between different groups of MROTs. The Intra-group consistency specifies the consistency requirement within a group of MROTs and the inter-group consistency specifies the consistency requirement between different groups of MROTs. The performance of the proposed algorithms is examined through a series of simulation experiments.