Client-Server Database Model Quiz

Client Server Database Model

• Client-Server Database model utilizes a dedicated server to store and execute the Database Management System (DBMS) within a network environment.
• Clients access the DBMS through the server.
• Clients rely on the server for database access, lacking direct interaction with the database.
• Servers process requests, retrieve data, and transmit it back to clients.
• Benefits include multi-user access, enabling concurrent access by multiple users.
• Access is unrestricted, enabling various users and applications to interact simultaneously.
• Concurrent access introduces challenges with simultaneous data retrieval, updates, and insertions.

Problems With Concurrent Access

• Lost update problem: Occurs when multiple clients simultaneously update data, potentially causing one client to overwrite another's changes, leading to data loss.
• Example Lost Update Problem: Three travel agencies (London, Birmingham, Swindon) with data stored in London.
• Birmingham and Swindon simultaneously access the data.
• Birmingham sells 3 seats.
• Swindon sells 5 seats, overwriting Birmingham's update due to differing processing times.
• Birmingham's update is lost, demonstrating the lost update problem.

Solutions for Lost Update Problem

• Record locks: The DBMS locks specific data records (e.g., available seats) during modification. This ensures only one client can modify the data at a time, preventing concurrent updates.
• Serialization: Transactions are processed sequentially in the order they are received. Guarantees data integrity but can lead to transaction failures if resources are depleted (e.g., all seats sold out).
• Timestamp Ordering: Each transaction includes a read and write timestamp. If a transaction modifies data that has been read and written to since the previous timestamp, the write attempt fails. The transaction restarts with the updated data.
• Commitment Ordering: An algorithm evaluates transaction characteristics and prioritizes transactions to prevent deadlocks and conflicts.

Applying Solutions to Airline Bookings

• Record locks: For individual seats instead of the whole database, enabling concurrent bookings for separate seats.
• Record locks: The lock is temporary, releasing it if a booking isn't completed within a period (e.g., 15 minutes).
• Serialization: Transactions might fail when all seats are sold, potentially causing customer frustration when trying to book different flights concurrently.
• Timestamp ordering: Implementing this needs frequent timestamp checks, leading to computational overhead, thus potentially making it impractical for airline booking systems.

Conclusion

• The lesson explains the client-server database model, concurrent access challenges, and solutions like record locks, serialization, timestamp ordering, and commitment ordering.
• It highlights solutions' practical applications in airline bookings, showcasing the trade-offs and real-world considerations of each method.

Test your knowledge on the Client-Server Database model and its functionalities. This quiz will cover topics such as the role of servers, benefits of multi-user access, and problems associated with concurrent access. Challenge yourself with examples like the lost update problem.