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Transactions, Concurrency Control and Recovery PYQs for GATE CS

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Question 1

2026 Slot Set2 PYQ

Consider concurrent execution of two transactions T_{1} and T_{2} in a DBMS, both of which access a data object A . For these two transactions to not conflict on A, which one of the following statements must be true?

Question 2

2025 Slot Set2 PYQ

An audit of a banking transactions system has found that on an earlier occasion, two joint holders of account A attempted simultaneous transfers of Rs. 10000 each from account A to account B . Both transactions read the same value, Rs. 11000, as the initial balance in A and were allowed to go through. B was credited Rs. 10000 twice. A was debited only once and ended up with a balance of Rs. 1000. Which of the following properties is/are certain to have been violated by the system?

Question 3

2025 Slot Set2 PYQ

Consider the database transactions T1 and T2, and data items X and Y. Which of the schedule(s) is/are conflict serializable? Transaction T1 R1(X) W1(Y) R1(X) W1(X) COMMIT(T1) Transaction T2 W2(X) W2(Y) COMMIT(T2)

Question 4

2025 Slot Set1 PYQ

A schedule of three database transactions T_{1}, T_{2}, and T_{3} is shown. R_{i} (A) and W_{i} (A) denote read and write of data item A by transaction T_{i}, i = 1, 2, 3 . The transaction T_{1} aborts at the end. Which other transaction(s) will be required to be rolled back? R_{1} (X) W_{1} (Y) R_{2} (X) R_{2} (Y) R_{3} (Y) A B O R T (T_{1})

Question 5

2024 Slot Set2 PYQ

Which of the following statements about the Two Phase Locking (2PL) protocol is/are TRUE?

Question 6

2024 Slot Set2 PYQ

Once the DBMS informs the user that a transaction has been successfully completed, its effect should persist even if the system crashes before all its changes are reflected on disk. This property is called

Question 7

2024 Slot Set1 PYQ

Consider the following read-write schedule S over three transactions T_{1}, T_{2}, and T_{3}, where the subscripts in the schedule indicate transaction IDs: S : r_{1} (z); w_{1} (z); r_{2} (x); r_{3} (y); w_{3} (y); r_{2} (y); w_{2} (x); w_{2} (y); Which of the following transaction schedules is/are conflict equivalent to S ?

Question 8

2022 PYQ

Let R_{i} (z) and W_{i} (z) denote read and write operations on a data element z by a transaction T_{i}, respectively. Consider the schedule S with four transactions. S : R_{4} (x) R_{2} (x) R_{3} (x) R_{1} (y) W_{1} (y) W_{2} (x) W_{3} (y) R_{4} (y) Which one of the following serial schedules is conflict equivalent to S ?

Question 9

2021 Slot Set2 PYQ

Let S be the following schedule of operations of three transactions T_{1}, T_{2} and T_{3} in a relational database system: R_{2} (Y), R_{1} (X), R_{3} (Z), R_{1} (Y), W_{1} (X), R_{2} (Z), W_{2} (Y), R_{3} (X), W_{3} (Z) Consider the statements P and Q below: P: S is conflict-serializable. Q: If T_{3} commits before T_{1} finishes, then S is recoverable. Which one of the following choices is correct?

Question 10

2021 Slot Set1 PYQ

Let r_{i} (z) and w_{i} (z) denote read and write operations respectively on a data item z by a transaction T_{i} . Consider the following two schedules. S_{1} : r_{1} (x) r_{1} (y) r_{2} (x) r_{2} (y) w_{2} (y) w_{1} (x) S_{2} : r_{1} (x) r_{2} (x) r_{2} (y) w_{2} (y) r_{1} (y) w_{1} (x) Which one of the following options is correct?

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Transactions, Concurrency Control and Recovery PYQs for GATE CS

Solve 11+ Transactions, Concurrency Control and Recovery previous year questions for GATE CS with answers and detailed solutions. Free sample questions below.

Chapter Roadmap: Transactions, Concurrency, and Recovery

ACID Properties and Concurrency Anomalies

The foundation. Defines the rules of reliability and the specific logical errors that occur when concurrent transactions interfere.

Conflict Serializability and Schedule Equivalence

The mathematical test. How to prove that an interleaved execution is logically equivalent to a safe, serial execution.

Recoverability, Cascading Rollback, and Crash Recovery

Handling failures. Ensuring that aborted transactions do not corrupt committed ones, and the database can restart cleanly.

Two-Phase Locking and Lock-Based Concurrency Control

The practical protocol. The actual mechanism databases use to guarantee serializability and prevent anomalies in real time.

The Transaction: A Logical Unit of Work

A transaction is a logical unit of work that contains one or more database operations (reads and writes).

From the system's perspective, it is a sequence of low-level operations. From the user's perspective, it is a single, indivisible action.

Core Principle

A transaction must transition the database from one consistent state to another consistent state. It is the fundamental boundary for enforcing reliability, concurrency control, and recovery.

Example: A funds transfer is one transaction. It involves:

Read balance of Account A.
Subtract amount from Account A.
Write new balance to Account A.
Read balance of Account B.
Add amount to Account B.
Write new balance to Account B.

If any step fails, the entire transaction is treated as if it never happened.

Transactions, Concurrency Control and Recovery: Solved Questions with Step-by-Step Explanations (10 Problems)

Question 1 · Databases · 2026_Set2 MCQ

Consider concurrent execution of two transactions $T_{1}$ and $T_{2}$ in a DBMS, both of which access a data object $A$ . For these two transactions to not conflict on $A$ , which one of the following statements must be true?

A.
Both $T_{1}$ and $T_{2}$ only read $A$
B.
$T_{1}$ reads $A$ and $T_{2}$ writes $A$
C.
$T_{1}$ writes $A$ and $T_{2}$ reads $A$
D.
Both $T_{1}$ and $T_{2}$ write $A$

Question 2 · Databases · 2025_Set2 MSQ

An audit of a banking transactions system has found that on an earlier occasion, two joint holders of account

A

attempted simultaneous transfers of Rs. 10000 each from account

A

to account

B

. Both transactions read the same value, Rs. 11000, as the initial balance in

A

and were allowed to go through.

B

was credited Rs. 10000 twice.

A

was debited only once and ended up with a balance of Rs. 1000.

Which of the following properties is/are certain to have been violated by the system?

A.
Atomicity
B.
Consistency
C.
Isolation
D.
Durability

Question 3 · Databases · 2025_Set2 MSQ

Consider the database transactions T1 and T2, and data items X and Y. Which of the schedule(s) is/are conflict serializable?

A.
R1(X), W2(X), W1(Y), W2(Y), R1(X), W1(X), COMMIT(T2), COMMIT(T1)
B.
W2(X), R1(X), W2(Y), W1(Y), R1(X), COMMIT(T2), W1(X), COMMIT(T1)
C.
R1(X), W1(Y), W2(X), W2(Y), R1(X), W1(X), COMMIT(T1), COMMIT(T2)
D.
W2(X), R1(X), W1(Y), W2(Y), R1(X), COMMIT(T2), W1(X), COMMIT(T1)

Question 4 · Databases · 2025_Set1 MCQ

A schedule of three database transactions

T_{1}

T_{2}

, and

T_{3}

is shown.

R_{i} (A)

and

W_{i} (A)

denote read and write of data item

A

by transaction

T_{i}

i = 1, 2, 3

. The transaction

T_{1}

aborts at the end. Which other transaction(s) will be required to be rolled back?

R_{1} (X) W_{1} (Y) R_{2} (X) R_{2} (Y) R_{3} (Y) A B O R T (T_{1})

A.
Only $T_{2}$
B.
Only $T_{3}$
C.
Both $T_{2}$ and $T_{3}$
D.
Neither $T_{2}$ nor $T_{3}$

Question 5 · Databases · 2024_Set2 MSQ

Which of the following statements about the Two Phase Locking (2PL) protocol is/are TRUE?

A.
2PL permits only serializable schedules
B.
With 2PL, a transaction always locks the data item being read or written just before every operation and always releases the lock just after the operation
C.
With 2PL, once a lock is released on any data item inside a transaction, no more locks on any data item can be obtained inside that transaction
D.
A deadlock is possible with 2PL

Question 6 · Databases · 2024_Set2 MCQ

Once the DBMS informs the user that a transaction has been successfully completed, its effect should persist even if the system crashes before all its changes are reflected on disk. This property is called

A.
durability
B.
atomicity
C.
consistency
D.
isolation

Question 7 · Databases · 2024_Set1 MSQ

Consider the following read-write schedule $S$ over three transactions $T_{1}, T_{2},$ and $T_{3}$ , where the subscripts in the schedule indicate transaction IDs:

$S : r_{1} (z); w_{1} (z); r_{2} (x); r_{3} (y); w_{3} (y); r_{2} (y); w_{2} (x); w_{2} (y);$

Which of the following transaction schedules is/are conflict equivalent to $S$ ?

A.
$T_{1} T_{2} T_{3}$
B.
$T_{1} T_{3} T_{2}$
C.
$T_{3} T_{2} T_{1}$
D.
$T_{3} T_{1} T_{2}$

Question 8 · Databases · 2022 MCQ

Let

R_{i} (z)

and

W_{i} (z)

denote read and write operations on a data element

z

by a transaction

T_{i}

, respectively. Consider the schedule

S

with four transactions.

S : R_{4} (x) R_{2} (x) R_{3} (x) R_{1} (y) W_{1} (y) W_{2} (x) W_{3} (y) R_{4} (y)

Which one of the following serial schedules is conflict equivalent to

S

A.
$T_{1} \to T_{3} \to T_{4} \to T_{2}$
B.
$T_{1} \to T_{4} \to T_{3} \to T_{2}$
C.
$T_{4} \to T_{1} \to T_{3} \to T_{2}$
D.
$T_{3} \to T_{1} \to T_{4} \to T_{2}$

Question 9 · Databases · 2021_Set2 MCQ

Let

S

be the following schedule of operations of three transactions

T_{1}

T_{2}

and

T_{3}

in a relational database system:

R_{2} (Y), R_{1} (X), R_{3} (Z), R_{1} (Y), W_{1} (X), R_{2} (Z), W_{2} (Y), R_{3} (X), W_{3} (Z)

Consider the statements P and Q below:

P: S is conflict-serializable.
Q: If

T_{3}

commits before

T_{1}

finishes, then S is recoverable.

Which one of the following choices is correct?

A.
Both P and Q are true.
B.
P is true and Q is false.
C.
P is false and Q is true.
D.
Both P and Q are false.

Question 10 · Databases · 2021_Set1 MCQ

Let

r_{i} (z)

and

w_{i} (z)

denote read and write operations respectively on a data item

z

by a transaction

T_{i}

. Consider the following two schedules.

S_{1} : r_{1} (x) r_{1} (y) r_{2} (x) r_{2} (y) w_{2} (y) w_{1} (x)

S_{2} : r_{1} (x) r_{2} (x) r_{2} (y) w_{2} (y) r_{1} (y) w_{1} (x)

Which one of the following options is correct?

A.
$S_{1}$ is conflict serializable, and $S_{2}$ is not conflict serializable.
B.
$S_{1}$ is not conflict serializable, and $S_{2}$ is conflict serializable.
C.
Both $S_{1}$ and $S_{2}$ are conflict serializable.
D.
Neither $S_{1}$ nor $S_{2}$ is conflict serializable.

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Personalised first. High quality throughout.

Built around you, not around a syllabus PDF

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Questions calibrated to the real exam

Notes written for recall, not for volume

One place for everything

Honest progress

Unlock the whole course

Transactions, Concurrency Control and Recovery PYQs for GATE CS

Chapter Roadmap: Transactions, Concurrency, and Recovery

The Transaction: A Logical Unit of Work

Transactions, Concurrency Control and Recovery: Solved Questions with Step-by-Step Explanations (10 Problems)

More previous year questions (pyqs) in this unit