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Describe Fragmentation- The storage of the data can be done by fragmenting the whole database into several pieces called fragments.
- Each of this fragment is stored at a different site.
- The logical data units stored at various sites in a distributed database system are known as fragments.
Advantages of fragmentation
1. Usage
- The applications work with views rather than the entire relations.
- It is appropriate to work with subsets of relation as the unit of distribution for data distribution.
2. Efficiency
- The data is stored where it is frequently used.
- Data which is not required by the local applications is not stored.
3. Parallelism
- A transaction can be divided into several sub queries that operate on fragments by using these fragments as a unit of distribution.
- This will help to increase the degree of concurrency, or parallelism, in the system, which in turn allows transactions to execute safely in parallel.
4. Security
- Data which is not required by the local applications is not stored which in turn is not available to unauthorized users.
Disadvantages of fragmentation
1. Performance
- The performance of global application which is required by the data from the several fragments which are located at different sites may be slower.
2. Integrity
- The integrity control can be difficult if the data and the functional dependencies are fragmented and are located at different sites.
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