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 r eplication contr ol scheme for mobile systems. Replicating data at multiple sites could contribute to enhance the availability r egading the distributed data. Replicating data, however , inevitably induces the bur den of maintaining r eplica consistency which r equires mor e complex synchr onisation mechanism, especially in the presence of excessive site failur es which could lead to global access br eakdown. In order for mobile workers to r eliably access global r eplicated databases without global access br eakdown, we devised a new scheme called fault-tolerant quor um consensus (FTQC). The main idea behind FTQC is that quor ums ar e allowed to be accessed fault-tolerantly by r esilient voting and defer red quorum-update pr otocols. We enhanced r esponsiveness of FTQC by dynamic quor um reconfiguration mechanism which minimizes r ollbacks. Based on the r esults of the performance evaluation, we conclude that FTQC schemes outperform the traditional schemes.