Partial Replication

Definition

A replicated database consists of a set of nodes ${\cal N}$ (database servers) and each logical data item x has a physical copy on a subset ${{\cal N}}_{x}$ of the nodes in ${\cal N}$. The replication degree ${r}_{x} = \vert {{\cal N}}_{x}\vert$ of a data item is the number of copies it has. Using full replication, each logical data item has a copy on each of the nodes, i.e., for each data item x of the database, ${{\cal N}}_{x} = {\cal N}$. Whenever there is at least one data item that does not have copies at all nodes, one refers to a partial replication architecture.

Key Points

Partial Replication can be used for different purposes:

Cluster Replication

In order to achieve scalability, data can be replicated across nodes residing in a single cluster. Read access to data items can then be distributed across the existing copies. Write operations, however, have to be performed on all copies. The potential for scalability can be best understood by a simple...