A Distributed Control Algorithm for Reliably and Consistently Updating Replicated Databases

This paper presents a deadlock-free and distributed control algorithm for robustly and consistently updating replicated databases. This algorithm is based on local locking and time stamps on lock tables which permit detection of conflicts among transactions executed at different sites. Messages are exchanged in the network whenever a transaction commitment occurs, that is, at the end of every consistent step of local processing. Conflicts among remote transactions are resolved by a roll back procedure. Local restart is based on a journal of locks which provides backup facilities. Performance in terms of the number of messages and volume of control messages of the proposed algorithm is compared with that of the voting and centralized locking algorithms. These results reveal that the proposed distributed control algorithm performs, in most cases, comparably to the centralized locking algorithm and better than the voting algorithm.