Recoverability and cascadeless schedules in DBMS Theory - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a recoverable schedule in database systems?

A recoverable schedule is one where transactions commit only after all transactions whose changes they depend on have committed. This ensures the database can be restored to a consistent state after failures.

beginner

Define a cascadeless schedule.

A cascadeless schedule is a schedule where transactions only read data written by committed transactions. This prevents cascading rollbacks, making recovery simpler.

intermediate

Why are cascading rollbacks problematic in databases?

Cascading rollbacks occur when one transaction failure causes multiple dependent transactions to roll back, leading to complex recovery and potential data inconsistency.

intermediate

How does a cascadeless schedule improve database recovery?

By ensuring transactions read only committed data, cascadeless schedules avoid cascading rollbacks, making recovery faster and simpler.

advanced

What is the relationship between recoverable and cascadeless schedules?

All cascadeless schedules are recoverable, but not all recoverable schedules are cascadeless. Cascadeless schedules are a stricter form that prevent cascading rollbacks.

What does a recoverable schedule ensure?

A Transactions commit immediately

B Transactions read uncommitted data

C Transactions commit only after dependent transactions commit

D Transactions never roll back

Recoverable schedules ensure that a transaction commits only after all transactions it depends on have committed.

Which schedule type prevents cascading rollbacks?

A Cascadeless schedule

B Non-recoverable schedule

C Recoverable schedule

D Dirty schedule

Cascadeless schedules prevent cascading rollbacks by allowing transactions to read only committed data.

What happens if a transaction reads uncommitted data and the writing transaction aborts?

A No effect on other transactions

B Cascading rollback occurs

C The reading transaction commits immediately

D The database becomes faster

Reading uncommitted data can cause cascading rollbacks if the writing transaction aborts.

Are all recoverable schedules cascadeless?

A Only in single transaction systems

B Yes, always

C Only if transactions never abort

D No, cascadeless is stricter

Cascadeless schedules are a stricter subset of recoverable schedules.

Which of the following is true about cascadeless schedules?

A They prevent cascading rollbacks

B They allow reading uncommitted data

C They are non-recoverable

D They increase rollback complexity

Cascadeless schedules prevent cascading rollbacks by restricting reads to committed data.

Explain what makes a schedule recoverable and why it is important for database consistency.

Think about when transactions are allowed to commit in relation to others.

Describe how cascadeless schedules help avoid cascading rollbacks and improve recovery.

Focus on the data read by transactions and its commit status.