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Tuesday, 12 August 2014
Advantages and Disadvantages of Data Replication in Distributed Database
Data replication is the process where in a relation (a table) or portion of a relation (a fragment of a table) is duplicated and those duplicated copies are stored in multiple sites (servers) to increase the availability of data.
“Replication is the process of copying (duplicating) and maintaining database objects in multiple databases that make up a distributed database system” – taken from Oracle Documentation.
1. Increased reliability and availability – We have many copies of same data in several different locations (usually different geographical locations). Hence, failure of any sites (servers) will not affect the transactions.
2. Queries requesting replicated copies of data are always faster (especially read queries) – Distributed database ensures the availability of data where it is needed much. In case of replication, this is one step ahead. Yes, the complete table itself loaded locally. Hence, those queries can be answered quickly from the local site where they are initiated.
3. Less communication overhead – When more number of read queries is generated in a site, all of them can be answered locally. Only the queries involving different table or the queries try to write something need to use the communication links to contact other sites.
1. More storage space is needed when compared to a centralized system – Replication would mean to duplicate any tables and store them in every site. This need more space in every site.
2. Update operation is costly – If we have more copies of same data loaded in different sites, obviously we need to update all the replicas whenever we would like to change data. Hence, write operation is always costly.
3. Maintaining data integrity is complex – It involves complex procedures to maintain consistent database.
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