NPTEL Introduction to Database Systems Week 12 Assignment Answers 2025
1. If all transactions follow 2PL protocol, the resulting schedules will always be serial schedules
- True
- False
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2. If all transactions follow 2PL protocol, the transaction that issues the first lock request in the schedule must also issue the first unlock request
- True
- False
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3. If all transactions follow 2PL protocol, deadlocks can be avoided
- True
- False
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4. If all transactions follow 2PL protocol, the transaction that issues the first lock request on a data item X must issue the first unlock request on X
- True
- False
Answer :-
5. Assuming that the recovery manager uses UNDO logging method, the value of B on disk immediately after restart, but before the recovery manager is activated, is:
- 20
- 40
- can’t be determined
- 10
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6. Again, assuming that the recovery manager uses UNDO logging method, consider the following set of commands issued by the recovery manager.
Cmd1: Restore A to 30 Cmd2: Restore A to 10 Which of the following statements is true as per the logging method?
- Cmd1 always precedes Cmd2
- Cmd1 is optional
- Cmd1 and Cmd2 are optional
- Cmd2 always precedes Cmd1
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7. Assuming that the recovery manager uses REDO logging method, the value of B on disk immediately after restart but before the recovery manager is activated.
- may be 20
- must be 20
- may be 40
- must be 40
Answer :-
8. In a particular database system, it is estimated that on an average (across many system crashes), the number of committed transactions is almost 5 times the number of uncommitted transactions in the log at the time of restart after the crash.. In which of the following logging mechanisms the recovery manager attends to the least number of transactions, after being given control after a crash?
- REDO
- UNDO
- UNDO-REDO
- Any of the above
Answer :-
9. Consider the following sets about system recovery after a crash
{1: UNDO; 2: REDO; 3: UNDO-REDO} {p: Ignore committed transactions; q: Consider committed transactions; r: Ignore committed and incomplete transactions; s: Consider committed and incomplete transactions; t: Write ahead log } Identify the correct matching between the sets:
- 1–p; 2–q; 3–r
- 1–t; 2–q; 3–s
- 1–p; 2–q; 3–t
- 1–p; 2–t; 3–s
Answer :-
10. Consider the following schedule S.
S: r1 (x); r2 (z); r1 (z); r3 (x); r3 (y); w1 (x); c1 ; w3 (y); c3 ; r2 (y); w2 (z); w2 (y); c2 Here ri (a) denotes transaction i reads item a, wi (a) denotes transaction i writes data item a, ci denotes that transaction i is committed. The transaction S is
- cascadeless and strict
- cascadeless and not strict
- not strict; cascadeless is irrelevant
- not cascadeless and not strict
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11. Consider the following schedule S.
S: r1 (x); r2 (z); r1 (z); r3 (x); r3 (y); w1 (x); w3 (y); r2 (y); w2 (z); w2 (y);
Here ri (a) denotes transaction i reads item a and wi (a) denotes transaction i writes data item a. The commit operations of the transactions can be added at the end of S in an appropriate order such that S is recoverable. The number of such orders is
- 1
- 2
- 3
- 4
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