JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III DISTRIBUTED DATABASES Previous Question Paper (August - 2022 - R18)

A Distributed Database Management System (DDBMS) is a software system that manages a distributed database while making the distribution transparent to the user. It integrates multiple autonomous database sites connected via a network, allowing users to access data as if it were stored in a single, centralized location.

The primary problem areas in a DDBMS environment include:

• Distributed Database Design: Deciding how to fragment data and where to allocate those fragments across sites to optimize performance.
• Query Processing: Translating high-level user queries into efficient execution plans that minimize data transfer across the network.
• Concurrency Control: Managing simultaneous access to data across multiple sites to ensure consistency and isolation.
• Reliability and Recovery: Ensuring the system remains operational despite site failures or communication link outages, and maintaining atomicity during distributed transactions.
• Distributed Deadlock Management: Detecting and resolving circular waiting conditions that can span multiple sites.

Transparency in a DDBMS is the separation of the higher-level semantics of the system from the lower-level implementation details. It allows users and application programs to operate on data without needing to know its physical location, fragmentation, or replication status.

The layers of transparency include:

• Data Independence (Fragmentation Transparency): Users are unaware that a logical relation is partitioned into fragments. Queries are written against the global relation, and the system handles the mapping to fragments.
• Location Transparency: Users do not need to know the physical location of the data. The command remains the same regardless of whether the data is local or remote.
• Replication Transparency: The system hides the existence of multiple copies of data. The user issues a single update, and the DDBMS ensures all replicas are updated consistently.
• Transaction Transparency: Ensures that distributed transactions maintain ACID properties, hiding the complexity of multi-site commit protocols like Two-Phase Commit (2PC).