Serializability in DBMS Theory - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Serializability in Transactions

Which of the following best describes the concept of serializability in database transactions?

A Transactions are executed in parallel without any restrictions to improve performance.

B The outcome of concurrent transactions is equivalent to executing them one after another without overlapping in time, ensuring consistency.

C Transactions are executed in any order as long as they do not access the same data items.

D Transactions are executed randomly and may cause inconsistent database states.

💡 Hint

Think about how transactions can be arranged to avoid conflicts and maintain database correctness.

Serializability means that the outcome of executing transactions concurrently is the same as if they were executed one after another in some order. This ensures data consistency.

📋 Factual

intermediate

Types of Serializability

Which type of serializability ensures that the order of conflicting operations is the same as in some serial schedule?

A Conflict serializability

B View serializability

C Recoverable schedule

D Cascadeless schedule

💡 Hint

Consider which type focuses on the order of conflicting operations like reads and writes.

Conflict serializability requires that conflicting operations (like read-write or write-write on the same data) appear in the same order as in a serial schedule.

🔍 Analysis

advanced

Analyzing Schedule Serializability

Given the following schedule of two transactions T1 and T2:

T1: R(A), W(A), R(B), W(B)
T2: R(B), W(B), R(A), W(A)

Is this schedule conflict serializable?

A No, because the schedule is not recoverable.

B Yes, because transactions access different data items without conflict.

C Yes, because the conflicting operations can be reordered to form a serial schedule.

D No, because the conflicting operations form a cycle in the precedence graph.

💡 Hint

Try drawing the precedence graph to check for cycles.

The schedule has conflicting operations on A and B in both directions, creating a cycle in the precedence graph, so it is not conflict serializable.

❓ Comparison

advanced

View Serializability vs Conflict Serializability

Which statement correctly compares view serializability and conflict serializability?

A All view serializable schedules are conflict serializable, but not all conflict serializable schedules are view serializable.

B View serializability and conflict serializability are exactly the same concepts.

C All conflict serializable schedules are view serializable, but not all view serializable schedules are conflict serializable.

D Neither view serializability nor conflict serializability guarantees serial execution equivalence.

💡 Hint

Think about which type is more general and which is more restrictive.

Conflict serializability is a stricter condition and is a subset of view serializability. Some schedules are view serializable but not conflict serializable.

❓ Reasoning

expert

Impact of Non-Serializable Schedules

What is the most likely consequence of allowing non-serializable schedules in a database system?

A The database may reach inconsistent states leading to incorrect query results.

B The database will always perform faster without any risk to data integrity.

C Transactions will never conflict, so concurrency control is unnecessary.

D The system will automatically convert non-serializable schedules into serial ones.

💡 Hint

Consider what happens if transactions interfere without proper ordering.

Non-serializable schedules can cause data inconsistencies because transactions may interfere in ways that violate correctness.