Deadlock handling in databases in DBMS Theory - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is a deadlock in database systems?

Which of the following best describes a deadlock situation in a database?

A A database server crashes due to hardware failure.

B Two or more transactions wait indefinitely for each other to release locks.

C A transaction fails due to syntax errors in SQL statements.

D A transaction commits successfully without any conflicts.

💡 Hint

Think about transactions waiting for resources held by others.

A deadlock occurs when two or more transactions are waiting for each other to release locks, causing an indefinite wait.

📋 Factual

intermediate

Which method is commonly used to detect deadlocks?

Which technique is typically used by database systems to detect deadlocks?

A Timeout mechanism that aborts transactions after a fixed time.

B Periodic backup of database logs.

C Wait-for graph analysis to find cycles indicating deadlocks.

D Indexing tables to speed up queries.

💡 Hint

Think about graphs representing waiting relationships.

Databases use wait-for graphs to detect cycles, which indicate deadlocks.

🚀 Application

advanced

What happens when a deadlock is detected?

When a deadlock is detected in a database, what is the usual action taken by the system?

A The system duplicates the locked data to avoid waiting.

B The system shuts down to prevent data corruption.

C The system ignores the deadlock and continues processing.

D The system rolls back one or more transactions to break the deadlock.

💡 Hint

Consider how the system can resolve waiting cycles.

To resolve deadlocks, the system aborts one or more transactions to free locks and break the cycle.

🔍 Analysis

advanced

Which scenario is an example of deadlock?

Consider two transactions T1 and T2. T1 holds a lock on resource A and waits for resource B. T2 holds a lock on resource B and waits for resource A. What does this scenario represent?

A Deadlock, because both transactions wait for each other’s locked resources.

B Normal transaction processing with no issues.

C Transaction starvation due to priority inversion.

D Data inconsistency caused by concurrent updates.

💡 Hint

Think about circular waiting conditions.

This is a classic deadlock where two transactions wait indefinitely for each other’s locks.

❓ Reasoning

expert

Why is deadlock prevention harder than deadlock detection?

Why is it generally more difficult for database systems to prevent deadlocks than to detect and resolve them?

A Prevention requires restricting transaction behavior upfront, which can reduce concurrency and performance.

B Detection algorithms are slower and less reliable than prevention methods.

C Prevention needs hardware support that is rarely available.

D Detection causes permanent data loss, while prevention does not.

💡 Hint

Consider the trade-offs between safety and performance.

Deadlock prevention restricts how transactions acquire locks, limiting concurrency and reducing system throughput, making it harder to implement effectively.