Increasing Data Availability for Unreliable Mobile Computers

Journal of Research and Practice in Information Technology, Vol. 32, No. 3/4, August/November 2000 181 We propose a new replication control scheme for mobile 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 synchronisation mechanism, especially in the presence of excessive site failures which could lead to global access breakdown. In order for mobile workers to reliably access global replicated databases without global access breakdown, we devised a new scheme called fault-tolerant quorum consensus (FTQC). The main idea behind FTQC is 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 FTQC schemes outperform the traditional schemes.