CLOUD DISTRIBUTED DATABASE

A distributed database is a database system that stores data in multiple locations instead of one location. This means that rather than putting all data on one server or on one computer, data is placed on multiple servers or in a cluster of computers consisting of individual nodes. These nodes are oftentimes geographically separate and may be physical computers or virtual machines within a cloud database.

There are two distinct types of distributed databases: homogeneous databases and heterogeneous databases.

In a homogeneous distributed database, the machines, nodes, servers, or sites store the same data, use the same data model, work with the same operating system, and share the same distributed database management system (DDBMS) or occasionally multiple types of DDBMS from the same vendor.

Within homogenous distributed databases, there are two subsets: autonomous and non-autonomous.

• Autonomous distributed databases: In an autonomous distributed database, nodes work on their own with their own complete set of data, only requiring an application to facilitate universal updates across all nodes or messaging between nodes.
• Non-autonomous distributed databases: In non-autonomous distributed databases, nodes rely on a centralized database management system (DBMS) to coordinate data distribution, communications, and all updates.

As a rule, homogeneous distributed databases offer significant data protection through redundancy and simplified management due to the similarity of all nodes.

In a heterogeneous distributed database, different machines or sites may house different data sets, use different operating systems, contain different data schemas, and require software to facilitate communication between machines. Further, different sites may not even be aware of the existence of other sites.

Within heterogeneous distributed databases, there are two subsets: federated and unfederated.

• Federated distributed databases: In a federated distributed database, multiple nodes — which are able to function completely on their own and may contain different data — can work together and function as one entity. This means that when a query occurs, the system determines which node is best equipped to respond and passes the query appropriately. This process is sometimes referred to as data virtualization.
• Unfederated distributed databases: In an unfederated distributed database, each node operates individually and there is a central application that manages the access to each database in each node.

While more complex to manage, heterogeneous distributed databases offer more flexibility in terms of data models, schema choices, and the types of data that can be stored than homogeneous distributed databases.