A transaction for which all committed changes are permanent is called:
Answer: D
Correct answer: durable
Durability means that once a transaction has committed, its changes are permanent and survive any subsequent failure. It is achieved by writing to a log on stable storage before the commit is acknowledged.
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A cursor type in which the application can only move forward through the recordset is called:
Answer: A
Correct answer: forward only.
A forward-only cursor can move through the recordset in one direction and cannot return to a row it has passed. It is the cheapest kind, since nothing needs to be retained behind the current position, and it is the right choice whenever the application simply processes each row once.
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A phantom read occurs when a transaction rereads data it has previously read and finds modifications or deletions caused by a committed transaction.
Answer: B
Correct answer: False
What is described is a nonrepeatable read: rows already seen have been modified or deleted by a committed transaction. A phantom read is the appearance of new rows that were not there before. The distinction decides which isolation level is needed, since repeatable read prevents the first but not the second.
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In this instance, dirty reads are disallowed, while nonrepeatable reads and phantom reads are allowed.
Answer: A
Correct answer: Read committed
Read committed guarantees only that data read has been committed by someone, so dirty reads are impossible. It takes no long-term read locks, so a row may change between two reads within the same transaction - a non-repeatable read - and new rows may appear, a phantom. It is the default level in most systems, as a compromise between correctness and concurrency.
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A transaction is a series of actions to be taken on the database so that either all of them are performed successfully or none of them are performed at all.
Answer: A
Correct answer: True
This is the definition of a transaction and it is the atomicity property stated in full. The series of actions is treated as a single indivisible unit, so a transfer between two accounts either debits one and credits the other or does neither - the database is never left with the money in neither place.
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The overall responsibility of the DBA is to facilitate the development and use of the database.
Answer: A
Correct answer: True
The DBA’s role is to facilitate the development and use of the database rather than to own the data or to write the applications. In practice that covers design support, security administration, backup and recovery, performance, configuration control and the arbitration of conflicting requirements between user groups.
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Which of the following locks the item from change but not from read?
Answer: D
Correct answer: Shared lock
A shared lock permits other transactions to read the item but not to change it, so any number of readers may hold one at once. An exclusive lock permits neither reading nor writing by anyone else. The pair is what allows concurrent reads to proceed freely while any write is serialised.
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