Distributed Databases Questions Long
A distributed data dictionary is a component of a distributed database system that stores and manages metadata information about the data stored across multiple nodes or sites in the distributed environment. It serves as a central repository for storing and organizing information about the structure, organization, and relationships of the data distributed across different database nodes.
The primary function of a distributed data dictionary is to provide a unified view of the distributed database system to the users and applications. It acts as a directory or catalog that contains metadata information such as table definitions, attribute details, data types, constraints, indexes, and relationships between tables. This metadata is essential for understanding the structure and organization of the distributed data, enabling efficient data access and manipulation.
The distributed data dictionary functions by maintaining consistency and synchronization of metadata across all the nodes in the distributed database system. It ensures that any changes made to the metadata, such as creating or modifying tables, attributes, or relationships, are propagated to all the relevant nodes. This ensures that all nodes have an up-to-date and consistent view of the distributed data.
Furthermore, the distributed data dictionary provides a mechanism for resolving naming conflicts and maintaining data integrity. It assigns unique names or identifiers to tables, attributes, and other database objects to avoid naming conflicts that may arise due to the distributed nature of the database system. It also enforces data integrity constraints by storing and enforcing referential integrity rules and other constraints defined on the distributed data.
In addition to maintaining metadata consistency, the distributed data dictionary also plays a crucial role in query optimization and execution. It stores statistical information about the data distribution, such as the number of rows in each table, the cardinality of attributes, and the distribution of values. This statistical information is used by the query optimizer to generate efficient query execution plans by estimating the cost of different query plans and selecting the most optimal one.
Overall, a distributed data dictionary acts as a central repository of metadata information in a distributed database system, providing a unified view of the distributed data to users and applications. It ensures metadata consistency, resolves naming conflicts, enforces data integrity, and aids in query optimization and execution, thereby facilitating efficient and effective management of the distributed database system.