In the design of data distribution the following objectives should be taken into account:
Processing
Locality: Distributing data to maximize processing locality
corresponds to the simple principle of placing data as close as possible to the
application which use them.
Designing data distribution for maximizing locality can be done by adding the number of local and remote reference corresponding to each candidate fragmentation and fragment allocation and selecting the best solution among them.
Availability
& Reliability of Distributed Data: A high
degree of availability for read-only application is achieved by storing
multiple copies of the same information; the system must be able to switch to
an alternative copy when the one that should be accessed under normal condition
is not available.
Reliability also achieved by storing multiple choices of some information since it is possible to recover from crashes or from the physical distribution of one of the copies by using the other, still available copies.
Workload Distribution: The workload distribution over the sites is an important feature of distributed computer system. Workload distribution is done in order to take advantage of the different powers or utilisation of computers at each site and to maximize the degree of parallelism of execution of application since workload distribution might negatively affect processing locality, it is necessary to consider the trade-off between them in the design of data distribution.
Storage
Costs and Availability: Database distribution should
reflect have Cost and availability of storage at the different sites. It is
possible to have specialized sites in the network for data storage, or conversely
to have sites which do not support mass storage at all.
