We propose a new concurrency control scheme for multiple-copy consistency in mobile database systems. Replicating data at multiple sites could contribute to enhance the availability regarding the distributed data. Replicating data, however, inevitably induces the burden of maintaining replica consistency which requires more complex synchronization mechanism, especially in the presence of network partitioning failures and site failures. Note that these failures could lead to access starvation or global access failure.
In order for mobile users to reliably access global replicated databases without access starvation and global access failure, we devise a new concurrency control scheme called fault-tolerant quorum consensus (FTQC). The main idea behind FTQC is that quorum formulation is allowed even in the minor partition by global-token circulation protocol and that quorums are allowed to be accessed fault-tolerantly by resilient voting and deferred quorum-update protocols. We enhanced responsiveness of FTQC by dynamic quorum reconfiguration mechanism which minimizes rollbacks. Based on the results of the performance evaluation, we conclude that the protocols which exploit FTQC scheme outperform the traditional protocols which never exploit FTQC.