Fault-Tolerant Quorum Consensus Scheme for Replication Control in Mobile Distributed Database Systems

We propose a new replication control scheme for multiple-copy consistency in mobile distributed 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 communication failures. If a communication link fails, all sites in the overall network are divided into two disjoint groups: the major group called quorum partition and the minor group called non-quorum partition. Note that this phenomenon called network partitioning could lead to access starvation in the non-quorum partition. In order for mobile users to access global databases without access starvation even in the presence of network partitioning, we propose a new scheme called fault-tolerant quorum consensus(FTQC). FTQC is based on the idea that quorum formation is allowed even in the non-quorum partition by circulating a single global token. FTQC guarantees a new form of one-copy serializability, inter-partition one-copy serializability, without sacrificing data availability. Based on the results of the performance evaluation, we conclude that the protocols which exploit FTQC scheme outperform the protocols which never exploit FTQC.