中文摘要：

数据网格系统通常采用副本技术提高系统总体性能，传统副本放置技术通过总体QoS需求确定副本数目和部署方式．针对QoS需求严格的一类数据网格应用，建立了个体服务质量受限的数据网格模型IQDG，提出一种启发式个体QoS受限的副本放置算法qGREP和基于逻辑环结构的一致性维护方法．IQDG采用的启发信息综合考虑了个体QoS约束的满足和副本开销的控制，能获得合理的副本策略．理论分析论证了算法的正确性和收敛性，模拟实验结果表明了算法能有效解决个体QoS受限的副本放置问题，在多种网络拓扑、访问模式和负载条件下均能取得较好的访问效果．

英文摘要：

As an important strategy for reducing access time, balancing overload, and obtaining high data availability, replication is widely used in distributed systems such as data grids. Currently grid researchers often consider replica management problem from the viewpoint of whole systems, ignoring individual QoS requirements of each single request. With the rapid growth of QoS-sensitive data grid applications, fulfilling QoS requirements of every request becomes a big challenge. In this paper, a new problem called individual QoS-restricted replica placement problem is defined, which is proved to be NP-hard. As traditional methods cannot solve such problem, a QoS-restricted data grid model named IQDG is then built. Based on IQDG, a novel replica placement algorithm called qGREP is presented. The algorithm utilizes profit value as heuristic information, which considers both the fulfillment of individual QoS-restrietion and the diversification of replica cost. In order to guarantee replica consistency, a logical ring-based updating mechanism is also proposed. IQDG takes individual QoS requirements of each request into account, and obtains rational replica policy by achieving tradeoff between the consistency cost and the access efficiency. Analysis reveals the internal relationship between network topology, user access pattern and overload. Experiments show that the model and algorithm are feasible and effective in complex data grid environment and can achieve good performance under different simulating conditions.