Commit Protocol in Distributed Database - Questions with Answers

Questions and Answers in Distributed Database Management System - Commit Protocols / Distributed Database Question and Answers on the topic Commit Protocols / Practice Exam Questions with Answers in Distributed Database / Advanced Database Systems Questions and Answers

Commit Protocols - Questions and Answers in Distributed Database Management System

Click on the questions for answers:

1. What are the types of failures we need to care about in distributed database?

2. List the control messages used in Two Phase Commit (2PC) protocol.

3. Explain the procedure used by 2PC for committing a transaction.

4. 

Figure 1 - Execution of Transaction T in a distributed environment

Figure 1 shows a distributed database configured on sites A, B, C, and D. All the sites are connected. Assume that a request in the form of Transaction T is reaching Site A. For this case represented in Figure 1, answer the following questions;

(a) How do you handle and restore(recover) the database if Site A is failed duringtransaction T? Explain.

(b) How do you handle and restore(recover) the database if Site B is failed duringtransaction T? Explain.

(c) Assume that the Site C is failed. When it recovers from failure, it reads<ready T> control message for transaction T in its log file. How wouldsite C restore the database using the <ready T> control message?

(d) Assume that the Site C is failed. When C recovers, it checks the log file for decidingthe fate of the transactions that were running during failure. This step isvery much necessary as it can lead the database to a consistent state. When you check thelog file, what are the different cases or log entries which would force you to performan Undo(T) (undo a transaction) on your own without consulting the other sites?

5.

Figure 2 - Execution of Transaction T in a distributed environment

Figure 2 shows a distributed database consists of sites A, B, C, and D. The connections between different sites are shown in dashed lines. Answer the following questions;

(a) Assume that Site A initiates transaction T, and both Site A and Site C contains data for executing transaction T. Also assume that the link between Site A and Site D is failed. What is the effect of the link failure in handling the transaction T?

(b) Assume that the transaction T which is initiated at Site A need to be executed at all the sites (Site A, B, C, and D). If the communication link between Site A and Site B is failed, how does Site B can handle the situation?

6. In 2PC protocol, the coordinator failure is considered as the major disadvantage of 2PC protocol. Why?

7. What is In-doubt Transaction?

8. How is Persistent Messaging (an alternate way to perform transaction processing) implemented?

9. What are the advantages and disadvantages of 3 Phase Commit protocol?

10. Why do we need the commit protocol in a distributed transaction?

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