By Bettina Kemme, Ricardo Jiménez Peris, Marta Patiño-Martínez, M. Tamer Özsu
Database replication is customary for fault-tolerance, scalability and function. The failure of 1 database copy doesn't cease the method from operating as on hand replicas can take over the initiatives of the failed copy. Scalability may be accomplished by means of allotting the burden throughout all replicas, and including new replicas may still the weight elevate. ultimately, database replication delivers quick neighborhood entry, whether consumers are geographically dispensed consumers, if info copies can be found on the subject of consumers. regardless of its benefits, replication isn't really an easy strategy to practice, and there are various hurdles to beat. on the vanguard is copy regulate: assuring that information copies stay constant whilst updates ensue. There exist many choices in regard to the place updates can ensue and while adjustments are propagated to information copies, how adjustments are utilized, the place the replication software is found, and so on. a specific problem is to mix copy regulate with transaction administration because it calls for numerous operations to be taken care of as a unmarried logical unit, and it offers atomicity, consistency, isolation and sturdiness around the replicated procedure. The booklet presents a categorization of reproduction regulate mechanisms, provides numerous reproduction and concurrency keep watch over mechanisms intimately, and discusses a number of the concerns that come up whilst such ideas have to be carried out inside of or on best of relational database structures. desk of Contents: evaluation / 1-Copy-Equivalence and Consistency / simple Protocols / Replication structure / The Scalability of Replication / keen Replication and 1-Copy-Serializability / 1-Copy-Snapshot Isolation / Lazy Replication / Self-Configuration and Elasticity / different points of Replication
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In pure partial replication each node has only copies of a subset of the data items but no node contains a full copy of the database. In this case, it is possible that a transaction accesses a set of data items such that no node has copies of all of them. Thus, distributed transaction processing needs to be supported. This is complex as it requires exact knowledge of where data items reside. Also, the typical client interface for relational databases are SQL based, and SQL select statements can translate to read operations on many data items.
Therefore, this execution is not possible under strict 2PL 1 . • A third property is that 1-copy-atomicity is easily provided if there are no failures because at commit time all update operations have successfully executed at all replicas. Therefore, the commit will succeed at all replicas. • In order to handle failures, some extensions are necessary. First, if a replica fails, a failure detection mechanism needs to inform all surviving nodes. Second, active transactions that were local on the failed replica have to be terminated properly.
Database Replication by Bettina Kemme, Ricardo Jiménez Peris, Marta Patiño-Martínez, M. Tamer Özsu