P2P systems where the overlay topology is not rigid and there is no explicit association between the location of data and the location of nodes. Many unstructured p2p systems have power-law degree characteristics.
Published in Chapter:
Data Replication in P2P Systems
Vassilios V. Dimakopoulos (University of Ioannina, Greece), Spiridoula Margariti (University of Ioannina, Greece), Mirto Ntetsika (University of Ioannina, Greece), and Evaggelia Pitoura (University of Ioannina, Greece)
Copyright: © 2010
|Pages: 27
DOI: 10.4018/978-1-61520-686-5.ch025
Abstract
Maintaining multiple copies of data items is a commonly used mechanism for improving the performance and fault-tolerance of any distributed system. By placing copies of data items closer to their requesters, the response time of queries can be improved. An additional reason for replication is load balancing. For instance, by allocating many copies to popular data items, the query load can be evenly distributed among the servers that hold these copies. Similarly, by eliminating hotspots, replication can lead to a better distribution of the communication load over the network links. Besides performance-related reasons, replication improves system availability, since the larger the number of copies of an item, the more site failures can be tolerated. In this chapter we survey replication methods applicable to p2p systems. Although there exist some general techniques, methodologies are distinguished according to the overlay organization (structured and unstructured) they are aimed at. After replicas are created and distributed, a major issue is their maintenance. We present strategies that have been proposed for keeping replicas up to date so as to achieve a desired level of consistency.