Data Replication in Distributed Databases


Data Replication in Distributed Databases

Data replication is the process of storing separate copies of the database at two or more sites.

Advantages of Data Replication

  • —Reliability − In case of failure of any site, the database system continues to work since a copy is available at another site(s).
  • —Reduction in Network Load − Since local copies of data are available, query processing can be done with reduced network usage, particularly during prime hours. Data updating can be done at non-prime hours.
  • —Quicker Response − Availability of local copies of data ensures quick query processing and consequently quick response time.
  • —Simpler Transactions − Transactions require less number of joins of tables located at different sites and minimal coordination across the network. Thus, they become simpler in nature.

Disadvantages of Data Replication

  • —Increased Storage Requirements − Maintaining multiple copies of data is associated with increased storage costs. The storage space required is in multiples of the storage required for a centralized system.
  • —Increased Cost and Complexity of Data Updating − Each time a data item is updated, the update needs to be reflected in all the copies of the data at the different sites. This requires complex synchronization techniques and protocols.
  • —Undesirable Application – Database coupling − If complex update mechanisms are not used, removing data inconsistency requires complex co-ordination at application level. This results in undesirable application – database coupling.