Question

Choose the correct answer for each of the following multiple-choice questions: To cope with media (disk) failures, it is necessary a. for the DBMS to only execute transactions in a single user environment. b. to keep a redundant copy of the database. c. to never abort a transaction. d. all of the above.

Short answer

The correct answer to the question is option B: to keep a redundant copy of the database.

Step-by-step solution

Explanation and Evaluation of Option A

Option A suggests that handling disk failures requires the DBMS to only execute transactions in a single user environment. While limiting the number of users could simplify management issues, it would not inherently guard against disk failures. Therefore, option A does not offer an appropriate solution to the problem statement.

Explanation and Evaluation of Option B

Option B suggests maintaining a redundant copy of the database to cope with disk failures. This solution indeed offers an effective way to ensure data integrity in the event of a failure. When a disk with the primary data fails, the system can resort to the redundant copy. Therefore, option B is a valid solution.

Explanation and Evaluation of Option C

Option C proposes to never abort a transaction. However, not aborting a transaction would not guarantee the database's protection from disk failures. In some cases, it might be necessary to abort transactions to maintain data integrity. Therefore, option C is not an accurate solution.

Explanation and Evaluation of Option D

Option D suggests that all the above solutions are necessary. However, we have already determined that options A and C are not appropriate solutions. Therefore, option D is also not correct.

Key concepts

Disk Failures

Disk failures occur when the physical storage device—known commonly as a disk—experiences issues that prevent it from reading or writing data properly. These failures can arise due to hardware malfunctions, such as wear and tear over time, or software corruption. When a disk failure happens, the data stored on it might become unavailable or even get corrupted. This poses a significant risk for database management systems (DBMS), as they rely on continuous, reliable access to data to function correctly. Understanding disk failures is crucial for designing resilient systems that can handle such events gracefully.

Data Integrity

Data integrity refers to the accuracy and consistency of data stored in a database. It is a foundational aspect of database management systems and is paramount in maintaining trust in the data stored. Ensuring data integrity means protecting data from unintended changes, corruption, or unauthorized access. When data integrity is compromised, it can lead to significant consequences, including incorrect decision-making, financial loss, or regulatory issues. Incorporating measures like validation processes, triggers, and more inherently robust database designs help to safeguard data integrity.

Redundant Copy

A redundant copy of a database is an additional, separate version of the database's data that is maintained to ensure availability in case of failure. This practice is known as redundancy and is a core strategy for dealing with disk failures. When you have a redundant copy, also referred to as a backup, you have a fallback option if the primary disk suffers damage. Data can still be accessed and restored from this redundant copy, minimizing downtime and preventing data loss. Regularly updating and testing these backups is essential to guarantee that the data stays current and usable during recovery efforts.

Transactions

Transactions are a sequence of operations performed as a single unit of work in database systems. They adhere to four key properties known as ACID (Atomicity, Consistency, Isolation, Durability).

• Atomicity: Ensures that all operations in a transaction are completed; otherwise, none are applied.
• Consistency: Ensures the database remains in a valid state before and after the transaction.
• Isolation: Ensures that transactions can occur independently without interference.
• Durability: Ensures that once a transaction is committed, it will remain so, even in the event of a failure.

Transactions are crucial for maintaining data integrity and consistency, especially in environments prone to disk failures.