What is distributed databases? What are the advantages and disadvantages?
Answers
Advantages
There are following advantages of DDBMs:
Reflects organizational structure
Many organizations are naturally distributed over several locations. For example, a bank has many offices in different cities. It is natural for databases used in such an application to be distributed over these locations. A bank may keep a database at each branch office containing details such things as the staff that work at that location, the account information of customers etc.
The staff at a branch office will make local inquiries of the database. The company headquarters may wish to make global inquiries involving the access of data at all or a number of branches.
Improved share ability and local autonomy
The geographical distribution of an organization can be reflected in the distribution of the data; users at one site can access data stored at other sites. Data can be placed at the site close to the users who normally use that data. In this way, users have local control of the data, and they can consequently establish and enforce local policies regarding the use of this data. A global database administrator (DBA) is responsible for the entire system. Generally, part of this responsibility is assigned the local level, so that the local DBA can manage the local DBMS.
Improved availability
In a centralized DBMS, a computer failure terminates the applications of the DBMS. However, a failure at one site of a DDBMS, or a failure of a communication link making\ some sites inaccessible, does not make the entire system in opera bite. Distributed DBMSs are designed to continue to function despite such failures. If a single node fails, the system may be able to reroute the failed node's requests to another site.
Improved reliability
As data may be replicated so that it exists at more than one site, the failure of a node or a communication link does not necessarily make the data inaccessible.
Improved Performance
As the data is located near the site of 'greatest demand', and given the inherent parallelism of distributed DBMSs, speed of database access may be better than that achievable from a remote centralized database. Furthermore, since each site handles only a part of the entire database, there may not be the same contention for CPU and I/O services as characterized by a centralized DBMS.
Economics
It is now generally accepted that it costs much less to create a system of smaller computers with the equivalent power of a single large computer. This makes it more cost effective for corporate divisions and departments to obtain separate computers. It is also much more cost-effective to add workstations· to a network than to update a mainframe system.
The second potential cost saving occurs where database are geographically remote and the applications require access to distributed data. In such cases, owing to the relative expense of data being transmitted across the network as opposed to the cost of local access, it may be much more economical to partition the application and perform the processing locally at each site.
Modular growth
In a distributed environment, it is much easier to handle expansion. New sites can be added to the network without affecting the operations of other sites.