Atomicity, consistency, isolation, and durability are easy words to recite. The difficulty begins when a question hides them inside a failed transfer, an integrity constraint, simultaneous updates, or a crash after commit, which is why keyword matching alone breaks down. The twelve previous-year questions below run from GATE 2005 to GATE 2025 and take in DSSSB, UGC NET, IBPS, TPSC and Beltron papers along the way, and every one of them yields to the same two steps: locate the event boundary, then map its clue to a single property. Build that decision map first, then use it instead of matching isolated keywords.
ACID properties in DBMS: build the four-way decision map first
A transaction is one logical unit of database work. The four guarantees answer different questions:
Property | Guarantee | Signal in the stem |
|---|---|---|
Atomicity | All operations happen, or none do | Partial work |
Consistency | Integrity constraints hold before and after | Valid-state rule |
Isolation | A concurrent result equals some serial execution | Simultaneous transactions |
Durability | Committed effects survive a later failure | Crash after commit |
Consider an INR 200 transfer. A starts at INR 1000 and B at INR 500, so the invariant total is INR 1500. A valid transfer produces A = INR 800 and B = INR 700. If failure occurs after only the debit, atomicity restores A = INR 1000 and B = INR 500. Consistency keeps the total at INR 1500, isolation makes concurrent transfers behave like a serial order, and durability preserves the committed A = INR 800, B = INR 700 state after a crash.
For the wider theory on schedules, locking and recovery, work through the DBMS learn module. In each answer below, identify the clue, name the property, and reject the nearest distractor.
Transaction processing basics and database access operations: Q1-Q3
Q1. DSSSB 2023
The main purpose of an ______ is to record, process, validate and store transactions that take place in various functional areas of a business for future retrieval of use.
Transaction Processing System
Decision Support System
Executive Support System
Knowledge Management System
Answer: Transaction Processing System (full solution on the practice page). The stem describes capturing, validating, processing, and storing routine business events. The other systems support decisions, executive summaries, or organisational knowledge, but they are not the primary transaction recorder.
Q2. DSSSB 2021
Which of the following statement(s) is/are correct regarding batch transaction processing?
I. The database is updated when the transaction is processed.
II. The associated cost is very high.
III. Reports generated are required only at a scheduled interval.
Only II
Only III
I and II
I and III
Answer: I and III (full solution on the practice page). A batch system collects transactions and updates the database when the batch is processed, with reports normally produced at scheduled intervals. Statement II is the distractor because batch processing is not defined by a very high associated cost.
Q3. UGC NET 2011
A transaction can include following basic database access operations:
Read_item(X)Write_item(X)Both (A) and (B)
None of these
Answer: Both (A) and (B), meaning Read_item(X) and Write_item(X) (full solution on the practice page). A transaction can read an item into its working state and write an updated value back within the same logical unit. Both operations are basic building blocks, so neither single-operation option is complete.
ACID full form in DBMS and the integrity distractor: Q4
Q4. TPSC 2025
What does the term “ACID” stand for in the context of a database?
Accuracy, Consistency, Integrity, Data
Atomicity, Consistency, Isolation, Durability
Authorization, Consistency, Integrity, Durability
Authentication, Consistency, Isolation, Data
Answer: Atomicity, Consistency, Isolation, Durability (full solution on the practice page). Atomicity makes a transaction all or nothing. Consistency preserves integrity constraints and valid states. Isolation separates concurrent effects, so I does not stand for integrity. Durability preserves a successful commit, while accuracy, authorisation, authentication, integrity, and data are not the four initials.
Atomicity and consistency MCQs: Q5-Q8
Q5. IBPS 2024
Which ACID property ensures that a transaction is executed entirely or not executed at all, so that partial updates are not permanently applied if a failure occurs during execution?
Consistency
Isolation
Recoverability
Atomicity
Durability
Answer: Atomicity (full solution on the practice page). “Entirely or not executed at all” identifies the all-or-nothing guarantee. Durability starts after a successful commit, while isolation concerns overlapping transactions.
Q6. IBPS 2025
A bank transfer debits money from one account but, due to system failure, does not credit it to the friend’s account. Which ACID property is violated?
Consistency
Atomicity
Isolation
Durability
Integrity
Answer: Atomicity (full solution on the practice page). With A = INR 1000, B = INR 500, and an INR 200 transfer, the partial A = INR 800, B = INR 500 state cannot remain. The transaction must finish at A = INR 800, B = INR 700 or roll back to A = INR 1000, B = INR 500.
Q7. IBPS 2023
Which ACID property ensures that a transaction brings the database from one valid state to another, maintaining all predefined rules?
Atomicity
Consistency
Isolation
Durability
None of the above
Answer: Consistency (full solution on the practice page). The clue is that every predefined rule and integrity constraint remains true in the resulting state. Atomicity asks whether the transaction completed as one unit, not whether its completed result is valid.
Q8. GATE 2015 and TPSC 2025
Consider the following transaction involving two bank accounts x and y.
read(x); x := x - 50; write(x); read(y); y := y + 50; write(y)
The constraint that the sum of the accounts x and y should remain constant is that of
Atomicity
Consistency
Isolation
Durability
Answer: Consistency (full solution on the practice page). If x = 500 and y = 300, the opening sum is 800. After moving 50, x = 450 and y = 350, and 450 + 350 = 800. All-or-nothing execution is atomicity, but the rule x + y = constant is a consistency constraint.
Isolation and durability MCQs: Q9-Q12
Q9. GATE 2025 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 INR 10000 each from account 𝐴 to account 𝐵. Both transactions read the same value, INR 11000, as the initial balance in 𝐴 and were allowed to go through. 𝐵 was credited INR 10000 twice. 𝐴 was debited only once and ended up with a balance of INR 1000. Which of the following properties is/are certain to have been violated by the system?
Atomicity
Consistency
Isolation
Durability
Answer: Consistency and Isolation (full solution on the practice page). Serially, the first transfer would take A from INR 11000 to INR 1000 and credit B INR 10000, and the second would then read INR 1000 and could not withdraw INR 10000 at all. Instead both read INR 11000, B was credited INR 20000, and A was debited once, so the second debit was lost, and no serial order can produce that outcome. Isolation is therefore broken. The totals show the second breach: if B started with b, the pair held INR 11000 + b before and INR 21000 + b after, so INR 10000 was created and consistency failed too. Nothing in the audit forces an atomicity or durability violation.
Q10. Beltron Programmer 2025
Which statement about durability is FALSE?
Durability guarantees immediate persistence to disk.
Durability can be compromised by storage media failures.
Durability requires non-volatile storage of committed data.
Log-based recovery mechanisms enforce durability.
Answer: Durability guarantees immediate persistence to disk (full solution on the practice page). Durability requires a committed effect to remain persistent and recoverable, but the changed data page need not reach its final disk location immediately. A write-ahead log or another non-volatile recovery record can secure the commit while later writes complete.
Q11. GATE 2024
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
durability
atomicity
consistency
isolation
Answer: durability (full solution on the practice page). “Successfully completed” followed by a crash is decisive because the commit has already been acknowledged and must be recoverable after restart. Atomicity governs an incomplete transaction, not the survival of an acknowledged commit.
Q12. GATE 2005
Amongst the ACID properties of a transaction, the 'Durability' property requires that the changes made to the database by a successful transaction persist
Except in case of an Operating System crash
Except in case of a Disk crash
Except in case of a power failure
Always, even if there is a failure of any kind
Answer: Always, even if there is a failure of any kind (full solution on the practice page). This is the only option that states durability without an exception. Inside the recovery model, an operating-system crash, a power failure, or a restart must not erase an acknowledged commit, because the commit record already sits in a write-ahead log on non-volatile storage. Q10's true statement about media failure is not a contradiction: exam keys treat durability as absolute within that model, while a physically destroyed disk sits outside it, which is why real deployments keep backups and mirrored logs.
ACID question traps: classify the failure before choosing an option
Clue | Property |
|---|---|
All or none, half-finished transaction | Atomicity |
Valid state, check constraint, invariant | Consistency |
Simultaneous work, lost update, as-if-serial result | Isolation |
After commit, crash, restart | Durability |
Use three passes. First, mark whether the failure occurs before or after commit. Second, check whether there is one transaction or overlapping work. Third, find an explicit invariant, such as Q8’s total of 800 or Q9’s preserved account total. You should now know the property before reading the options.
Atomicity and consistency overlap in a failed transfer, but atomicity asks whether the logical unit remained partial while consistency asks whether a database rule broke. Atomicity and durability both mention failure, but durability begins only after commit. Continue with the DBMS Transaction MCQs collection for schedules, serializability, and locking.
ACID properties MCQs: the short version and next step
Keep one line in memory: atomicity is completion, consistency is validity, isolation is concurrent equivalence, and durability is post-commit survival. Redo Q6, Q8, Q9, and Q11 without viewing the answers because together they separate the properties through actual failure scenarios.
Use the Introduction & ACID Properties module for topic practice and the GATE CS Exam Preparation category for the broader route. GATE Guidance by Sanchit Sir includes DBMS Transaction Management inside its wider GATE CS sequence.
