ENHANCED TREE QUORUM ALGORITHM FOR REPLICA CONTROL IN DISTRIBUTED DATABASE-SYSTEMS

In this paper, new replica control algorithms, called the enhanced tree quorum (ETQ) algorithm and the multiple tree quorum (MTQ) algorithm, are proposed to manage replicated data in distributed database systems. These algorithms provide high availability for read and write operations by imposing a logical structure of modified tree with a backup root on data copies in ETQ, and multiple trees on data copies in MTQ. With ETQ algorithm, a read operation is limited to a data copy in the best case, and a write operation is allowed as long as one of the roots and the majority of the children of each node selected are available in the tree. With MTQ algorithm, a read operation is limited to a couple of data copies, and a write operation is allowed as long as the majority of the roots of the trees and the majority of the children of each node selected are available. Compared to other algorithms, ETQ and MTQ require lower message cost for an operation, while providing higher availability.