What is used by a properly designed DBMS to enable databases to be returned to the pre-transaction state should errors occur?
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two phase commit
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prefetch transaction
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one phase commit
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backup and restore
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All of the above
A two-phase commit (2PC) is a distributed algorithm that ensures all participating nodes in a database transaction either commit or roll back. This atomicity allows the system to return to a consistent pre-transaction state if an error occurs during any part of the process.
To answer this question, we need to understand the concept of error handling and recovery in a database management system (DBMS).
Option A) Two-phase commit - This option is incorrect. Two-phase commit is a protocol used to ensure the atomicity and consistency of distributed transactions. It does not specifically deal with error recovery.
Option B) Prefetch transaction - This option is incorrect. Prefetching is a technique used to improve the performance of data retrieval by fetching data in advance. It is not directly related to error recovery.
Option C) One-phase commit - This option is incorrect. One-phase commit is a protocol used to commit a transaction in a distributed system. It does not specifically deal with error recovery.
Option D) Backup and restore - This option is correct. Backup and restore is a commonly used technique in DBMS to enable databases to be returned to a previous state in case of errors or failures. Regular backups are taken to create a copy of the database, and in case of errors, the database can be restored from the backup.
Option E) All of the above - This option is incorrect as not all of the options listed (A, B, and C) are correct. Only option D, backup and restore, is correct.
The correct answer is D) backup and restore. This option is correct because a properly designed DBMS uses backup and restore techniques to enable databases to be returned to the pre-transaction state should errors occur.