Replication transparency

In a distributed DBMS a relational table or a partition may be replicated or copied, and copies may be distributed throughout the database. This feature can cause problems for propagating updates and concurrency control and this is transparent to users in distributed databases.

By replication transparency in a distributed database we mean that partitioned/replicated updates must be propagated through all copies in existence. Replication is desirable and transparent.

Replication helps performance since diverse and conflicting user requirements can be more easily accommodated. For example, data that is commonly accessed by one user can be placed on that user’s local machine as well as on the locality of reference. Furthermore, if one of the machines fails, a copy of the data is still available on another machine on the network. Of course, this is a very simple description of the situation. In fact, the decision as to whether to replicate or not, and how many copies of any database object to have, depends to a considerable degree on user application.

Related Articles: Data independence, Network transparency, Fragmentation transparency.