Distributed databases - Concurrency Control


Concurrency control in distributed database / Various locking protocols in distributed database / Single lock manager and distributed lock manager approaches in handling concurrent transactions



Concurrency Control in Distributed Database

Concurrency control schemes dealt with handling of data as part of concurrent transactions. Various locking protocols are used for handling concurrent transactions in centralized database systems. There are no major differences between the schemes in centralized and distributed databases. The only major difference is that the way the lock manager should deal with the replicated data. The following topics discusses about several possible schemes that are applicable to an environment where data can be replicated in several sites. We shall assume the existence of the shared and exclusive lock modes.

Locking protocols
                                a) Primary Copy protocol
                                b) Majority protocol
                                c) Biased protocol
                                d) Quorum Consensus protocol

Some assumptions:
Our distributed database system consists of n sites (servers/computers in different locations)
Data are replicated in two or more sites



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