Increased overheads on update: On the drawbacks side, it will need the system to ensure that all replicas of a relation are consistent. This shows that all the replicas of the relation require to be updated at the similar time, resulting in increased overheads. For instance, in a banking system, if account information is replicated at several sites, it is essential that the balance in a particular account should be the similar at all sites.

The problem of controlling concurrent updates by various transactions to replicated data is more difficult than the centralised approach of concurrency control. The management of replicas of relation can be simplified by deciding one of the replicas as the primary copy. For instance, in a banking system, the primary copy of an account may be the site at which the account has been opened. Likewise, in an airline reservation system, the primary copy of the flight may be related with the site at which the flight originates.

Posted Date: 3/13/2013 8:30:46 AM | Location : United States

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