Various options for distributing databases / What are the different options for distributing databases over a distributed database system? / List the various possible options for distributing a database in a DDBS. / List and discuss the techniques for distributing a database
Various options for distributing databases
A database is distributed over network and
stored on various sites in geographically different locations for ease of
access. This we know earlier. In an actual case, a database may be stored in
multiple sites as it is, or some tables of a database might be stored at one
site, the others at some other site and so on. So, what are the various options
available to us to distribute database over different locations? They are,
1. Data replication – it is about keeping the same
copies at different sites.
·
The whole database may be reproduced and
maintained at all or few of the sites, or
·
A particular table may be reproduced and
maintained at all or few of the sites
2. Horizontal partitioning – it is about
partitioning a table by records without disturbing the structure of the table. For
example, if you have a table EMP which stores data according to a schema
EMP(Eno, Ename, Dept, Dept_location), then horizontal partitioning of EMP on
Dept_location is about breaking employee records according to the department location
values and store different set of employee details at different locations. The data
at different locations will be different, but the schema will be the same, ie.,
EMP(Eno, Ename, Dept, Dept_location).
3. Vertical partitioning – it is about partitioning a
table vertically, ie., decomposition. Hence, the partition of tables at
different locations will of different structure.
For example, assume the schema EMP(Eno,
Ename, Dept, Dept_location). If you would like to break the above schema like
one to store employee details and the other to store the department details, it
can be done as follows;
EMP(Eno, Ename, Dept), and DEPT(Dept,
Dept_location)
These two tables might be stored at different
locations for ease of access according to the defined organization policies for
example.
4. Hybrid approach – it is a combination of few or
all of the above said techniques. That is, it may be a combination like the few
listed below;
·
Horizontal partitioning and replication of few or
all horizontal partitions.
·
Vertical partitioning and replication of few or
all vertical partitions.
·
Vertical partitioning, followed by horizontal
partitioning of some vertical partitions, followed by replication of few
horizontal partitions, etc.
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