Distributed DBMS

A Distributed Database Management System (DDBMS) manages a collection of multiple, logically interrelated databases distributed over a computer network. Unlike a centralized system where all data resides in one location, a distributed database stores data across several physical sites. From the user's perspective, however, the database should look like a single, centralized database. This property is called 'transparency'. The main advantages of a DDBMS are increased reliability and availability. If one site fails, the rest of the system can continue to operate, and data might still be accessible if it is replicated elsewhere. They also allow for improved performance, as data can be stored closer to where it is used most frequently, reducing network latency, and queries can be processed in parallel across multiple sites. There are two main approaches to designing a DDBMS. In a homogeneous system, all sites use the same DBMS software, making it easier to manage. In a heterogeneous system, different sites might run different DBMS software (e.g., Oracle at one site, SQL Server at another), which is more complex but can be necessary when integrating pre-existing systems. Managing a DDBMS introduces significant challenges, including complex query processing, the need to maintain consistency across replicas, intricate concurrency control, and a more difficult recovery process compared to centralized systems. These challenges are fundamental to the design of large-scale, modern data systems.