Replicated Data Management in Distributed Database Systems

Replication is the key factor in improving the availability of data in distributed systems. Replicated data is stored at multiple sites so that it can be accessed by the user even when some of the copies are not available due to site failures. A major restriction to using replication is that replicated copies must behave like a single copy, i.e., mutual consistency as well as internal consistency must be preserved. Synchronization techniques for replicated data in distributed database systems have been studied in order to increase the degree of concurrency and to reduce the possibility of transaction rollback. In this paper, we classify different synchronization methods by underlying mechanisms and the type of information they use in ordering the operations of transactions, and survey some of the replication management methods appeared in the literature.