Paper 2 CS · UNIT 04 · MOCK TEST

Mock 8 – Transactions, Concurrency & Recovery

Unit 4: Database Management Systems · 28 questions · about 33 minutes. Press End Mock any time to see your score and the correct answers.

All 11 topic-wise mocks in this unit

0 / 28 answered 00:00

Q1. Match the LIST-I with LIST-II

LIST-I	LIST-II
A. Wait-for graph	I. Holds all locks until it commits
B. Precedence graph	II. Holds write-locks until it commits
C. Rigorous 2PL	III. Use to check deadlocks
D. Strict 2PL	IV. Used to check serializability

Choose the correct answer from the options given below:

AA-III, B-IV, C-I, D-II BA-III, B-IV, C-II, D-I CA-IV, B-I, C-II, D-III DA-IV, B-III, C-II, D-I

Q2. Consider the following statements:
A. A non-serial schedule is said to be conflict serializable if it is conflict-equivalent to some serial schedule.
B. A non-serial schedule is said to be view serializable if it is view-equivalent to some serial schedule.
C. A schedule is said to be serial if instructions of participating transactions are chronologically interleaved with each other.
D. A conflict-serializable schedule will be view-serializable also but vice-versa may not be true.
Choose the correct answer from the options given below:

AA, B, C, D BA, B, C Only CA, B, D Only DB, C, D Only

Q3. In concurrency control, the phantom problem may occur when

Arecords are inserted Brecords are deleted Crecords are modified Drecords are indexed

Q4. Consider the transactions T1, T2, T3 and the schedules S1 and S2 given below.
T1: r1(x); r1(z); w1(z)
T2: r2(y); r2(z); w2(z)
T3: r3(y); r3(x); w3(y)
S1: r1(x); r3(y); r3(x); r2(y); r2(z); w3(y); w2(z); r1(z); w1(x); w1(z)
S2: r1(x); r3(y); r2(y); r3(x); r1(z); r2(z); w3(y); w1(x); w2(z); w1(z)
Which one of the following statements about the schedules is TRUE?

AOnly S1 is conflict-serializable BOnly S2 is conflict-serializable CBoth S1 and S2 are conflict-serializable DNeither S1 nor S2 is conflict-serializable

Q5. Which of the following statements are CORRECT?
(A) Granularity is the size of data items in a database.
(B) Two operations in a schedule are said to be in conflict if they belong to the same transaction.
(C) Two schedules are said to be conflict equivalent if the order of any two conflicting operations is the same in both schedules.
(D) Write operations that are performed without performing the write operation are known as blind writes.
Choose the correct answer from the options given below:

A(A) and (B) Only B(A), (B) and (C) Only C(A), (B) and (D) Only D(B) and (C) Only

Q6. Which of the following scenarios may lead to an irrecoverable error in a database system?

AA transaction writes a data item after it is read by an uncommitted transaction BA transaction reads a data item after it is read by an uncommitted transaction CA transaction reads a data item after it is written by a committed transaction DA transaction reads a data item after it is written by an uncommitted transaction

Q7. Which one of the following is NOT a part of the ACID properties of a database transaction?

AAtomicity BConsistency CIsolation DDeadlock-freedom

Q8. Which of the following concurrency-control protocols ensures both conflict serializability and freedom from deadlock?
Statement I: Two-phase locking
Statement II: Timestamp ordering

ABoth Statement I and Statement II are correct BBoth Statement I and Statement II are incorrect CStatement I is correct but Statement II is incorrect DStatement I is incorrect but Statement II is correct

Q9. Which of the following is/are true in case of tree locking (the tree protocol)?
A. It ensures shorter waiting times.
B. It ensures freedom from deadlock.
C. A transaction can lock data items earlier.
D. It does not ensure a greater amount of concurrency.
Choose the correct answer from the options given below:

AA and B Only BC and D Only CB and C Only DA and D Only

Q10. The techniques used to handle the phantom problem are:
A. Time stamping
B. Index locking
C. Predicate locking
D. Execution indexing
Choose the correct answer from the options given below:

AA and B Only BB and C Only CA and D Only DC and D Only

Q11. Let T1 be a transaction that transfers Rs. 50 from account A to account B: 1 Read(A); 2 A := A − 50; 3 Write(A); 4 Read(B); 5 B := B + 50; 6 Write(B). What is the status of the database just after the 3rd step but before the 5th step?

AAlways consistent BMay be temporarily inconsistent CMust abort DAlways roll back

Q12. Match List I with List II

List I	List II
A. Timestamp protocol	I. As long as the transaction is running, it obtains the required locks in the first phase.
B. Strict two-phase locking protocol	II. Indicates the final lock of the schedule.
C. Two-phase locking	III. Ensures freedom from deadlock.
D. Lock point in two-phase locking protocol	IV. Ensures cascadeless rollback.

AA-III, B-IV, C-II, D-I BA-III, B-IV, C-I, D-II CA-IV, B-III, C-II, D-I DA-IV, B-II, C-I, D-III

Q13. Consider the schedule S (operations at successive timestamps t1–t6):
t1: T2 R(X), T3 R(Y)
t2: T2 W(X), T3 W(Y)
t3: T1 R(Y), T4 R(X)
t4: T1 W(Y), T4 W(X)
t5: T3 R(X)
t6: T3 W(X)
Choose the correct (conflict-equivalent) serial execution order for the schedule S.

AT3 − T2 − T1 − T4 BT2 − T3 − T1 − T4 CT2 − T4 − T3 − T1 DT4 − T2 − T3 − T1

Q14. Consider the following statements:
Statement I: Conservative 2PL is a deadlock-free protocol.
Statement II: Thomas's write rule enforces conflict serializability.
Statement III: The timestamp ordering protocol ensures serializability based on the order of transaction timestamps.
Which of the following is correct?

AStatements I and II true, Statement III false BStatements I and III true, Statement II false CStatements I and II false, Statement III true DStatements I, II and III true

Q15. What is called journaling in a Linux operating system?

AProcess scheduling BFile saving as transaction CA type of thread DAn editor

Q16.

In concurrency control, phantom problem may occur, when-

Arecords are inserted Brecords are deleted Crecords are modified Drecords are indexed

Q17.

Consider transactions T1: r1(x); r1(z); w1(z) T2: r2(y); r2(z); w2(z) T3: r3(y); r3(x); w3(y), and schedules S1: r1(x); r3(y); r3(x); r2(y); r2(z); w3(y); w2(z); r1(z); w1(x); w1(z) and S2: r1(x); r3(y); r2(y); r3(x); r1(z); r2(z); w3(y); w1(x); w2(z); w1(z). Which statement is TRUE?

AOnly S₁ is conflict-serializable BOnly S₂ is conflict-serializable CBoth S₁ and S₂ are conflict-serializable DNeither S₁ nor S₂ is conflict-serializable

Q18.

Which of the following scenario may lead to an irrecoverable error in a database system?

AA transaction writes a data item after it is read by an uncommitted transaction BA transaction reads a data item after it is read by an uncommitted transaction CA transaction reads a data item after it is written by a committed transactions DA transaction reads a data item after it is written by an uncommitted transaction.

Q19.

Given below are two statements: Which of the following concurrency control protocol ensures both conflict serializability and freedom from deadlock?

Statement I: Two phase locking

Statement II: Timestamp ordering In the light of the above statements, choose the most appropriate answer from the options given below:

Q20.

Let T1 transfer ₹50 from account A to account B: 1 Read(A); 2 A := A − 50; 3 Write(A); 4 Read(B); 5 B := B + 50; 6 Write(B). What is the state of the database just after step 3 but before step 5?

AAlways consistent BMay be temporarily inconsistent CMust be abort DAlways rollback

Q21.

Match List I with List II

AA-III, B-IV, C-II, D-I BA-III, B-IV, C-I, D-II CA-IV, B-III, C-II, D-I DA-IV, B-II, C-I, D-III

Q22.

Consider the schedule S: t1: R2(X), R3(Y); t2: W2(X), W3(Y); t3: R1(Y), R4(X); t4: W1(Y), W4(X); t5: R3(X); t6: W3(X). Choose the correct serial execution order equivalent to S.

AT3-T2-T1-T4 BT2-T3-T1-T4 CT2-T4-T3-T1 DT4-T2-T3-T1

Q23.

Statement I: Conservative 2PL is a deadlock-free protocol. Statement II: Thomas's write rule enforces conflict serializability. Statement III: Timestamp ordering ensures serializability based on the order of transaction timestamps. Which is correct?

AStatements I and II true, Statement III false BStatements I and III true, Statement II false CStatements I and II false, Statement III true DStatements I, II and III true

Q24.

A transaction may be in one of the following states during its execution life cycle in concurrent execution environment.

A. FAILED

B. TERMINATED

C. PARTIALLY COMMITTED

D. COMMITTED

E. ACTIVE Given a transaction in active state during its execution, find its next transitioned state from the options given below:

AA only BEither A or C only CC only DD only

Q25.

In the context of concurrency control, a given pair of operations in a schedule is called conflict schedule if

(A) At least one of the operations is write operation.

(B) Both the operations are performed on the same data item.

(D) Both the operations are performed on different data items.

A(A) and (B) only B(A), (B) and (C) only C(A), (C) and (D) only D(C) and (D) only

Q26.

Two concurrent executing transactions 1 and T 2 are allowed to update same stock item say ' A ' in an uncontrolled manner. In such scenario, following problems may occur :

(a) Dirty read problem

(b) Lost update problem

(d) Inconsistent database state Which of the following option is correct if database system has no concurrency module and allows concurrent execution of above two transactions?

A(a), (b) and (c) only B(c) and (d) only C(a) and (b) only D(a), (b) and (d) only

Q27.

Consider two transactions on account A (initial balance 20,000): T1 transfers 5,000 to account B, then T2 applies 10% interest to A. The log is:

(i) T1 start

(ii) T1, A, old = 20,000, new = 15,000

(iii) T1, B, old = 12,000, new = 17,000

(iv) T1 commit

(v) T2 start

(vi) T2, A, old = 15,000, new = 16,500 (vii) T2 commit Suppose the database crashes just before log record (vii) is written. When the system restarts, which statement is true of the recovery process?

AWe must redo log record (vi) to set A to 16,500 . BWe must undo log record (vi) to set A to 16,500 and then redo log records (ii) and (iii). CWe need not redo log records (ii) and (iii) because transaction T1 has committed. DWe can apply redo and undo operations in arbitrary order because they are idempotent.

Q28.

Consider the following schedules involving two transactions: S₁: r₁(X); r₁(Y); r₂(X); r₂(Y); w₂(Y); w₁(X) S₂: r₁(X); r₂(X); r₂(Y); w₂(Y); r₁(Y); w₁(X) Which one of the following statements is correct?

ABoth S₁ and S₂ are conflict serializable BBoth S₁ and S₂ are not conflict serializable CS₁ is conflict serializable and S₂ is not DS₁ is not conflict serializable and S₂ is

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