Deadlock handling in databases in DBMS Theory - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a deadlock in a database system?

A deadlock occurs when two or more transactions wait indefinitely for each other to release locks on resources, causing all involved transactions to stop progressing.

intermediate

Name one common method used to detect deadlocks in databases.

One common method is the wait-for graph, where transactions are nodes and edges represent waiting for locks. A cycle in this graph indicates a deadlock.

intermediate

What is deadlock prevention in databases?

Deadlock prevention involves designing the system to avoid conditions that can cause deadlocks, such as by ordering resource requests or using timeouts.

intermediate

How does deadlock resolution typically work in databases?

Deadlock resolution usually involves choosing one transaction as a victim and rolling it back to break the deadlock, allowing other transactions to continue.

beginner

Why is deadlock handling important in database management?

Deadlock handling is important to ensure that transactions do not get stuck forever, which would block other operations and reduce system performance and reliability.

What indicates a deadlock in a wait-for graph?

A A cycle in the graph

B A disconnected node

C A node with no edges

D A linear chain of nodes

A cycle in the wait-for graph means transactions are waiting on each other in a loop, which is a deadlock.

Which of the following is NOT a deadlock handling technique?

A Deadlock detection

B Deadlock prevention

C Deadlock avoidance

D Deadlock ignoring

Ignoring deadlocks is not a handling technique because it causes the system to hang indefinitely.

What action is taken to resolve a deadlock?

A Commit all transactions

B Restart the database server

C Rollback one or more transactions

D Increase lock timeout

Rolling back one or more transactions breaks the deadlock cycle and allows others to proceed.

Deadlock prevention can be achieved by:

A Allowing transactions to wait indefinitely

B Requesting all locks at once in a fixed order

C Ignoring lock requests

D Using random lock granting

Requesting locks in a fixed order prevents circular wait, a necessary condition for deadlocks.

Why is deadlock detection preferred over prevention in some systems?

A Prevention can reduce concurrency

B Detection avoids all deadlocks

C Detection is simpler to implement

D Prevention is slower

Prevention techniques can limit how transactions access resources, reducing system concurrency and performance.

Explain what a deadlock is in a database and why it happens.

Think about transactions waiting for locks held by each other.

Describe the main strategies used to handle deadlocks in databases.

Consider how systems avoid, find, or fix deadlocks.