Database administration refers to a function that applies to the entire organization.
Answer: B
Correct answer: False
The organisation-wide function is data administration, which concerns data as a corporate resource across all systems. Database administration is narrower, applying to a particular database and its applications - its design, security, backup, performance and configuration.
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A durable transaction is one in which all committed changes are permanent.
Answer: A
Correct answer: True
Durability is the last of the four ACID properties: once a transaction has committed, its changes survive whatever happens afterwards, including a crash. It is achieved by writing the change to the transaction log before acknowledging the commit, so that the change can be reapplied during recovery even if it never reached the datafiles.
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When one transaction reads a changed record that has not been committed to the database a filthy read occurs.
Answer: B
Correct answer: False
The name is right in substance and wrong in wording: reading a changed record that has not been committed is a dirty read, not a filthy one. The term matters because it is one of the three anomalies the isolation levels are defined against, alongside nonrepeatable reads and phantom reads.
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Dirty read, nonrepeatable, and phantom reads are not possible in this instance.
Answer: D
Correct answer: Serializable
Serializable is the strictest level and permits none of the three anomalies: no dirty reads, no nonrepeatable reads and no phantoms. It gives the same result as running the transactions one after another, which is where the name comes from. The cost is the concurrency given up to achieve it, which is why lower levels exist at all.
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Two transactions that run concurrently and generate results that are consistent with the results that would have occurred if they had run separately are referred to as serializable transactions.
Answer: A
Correct answer: True
Serializable transactions produce a result identical to some serial execution of the same transactions, one after another. It is the standard against which concurrency control is judged: the transactions may interleave in any way at all, so long as the outcome could have been produced by running them in some order.
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Which of the following refers to a cursor type that when the cursor is opened, a primary key value is saved for each row in the recordset; when the application accesses a row, the key is used to fetch the current values of the row?
Answer: C
Correct answer: Keyset
A keyset cursor saves the primary key of every row in the recordset when it is opened, and fetches the current values through that key each time a row is accessed. So changes made to rows already in the set are seen, but rows inserted afterwards are not, since their keys were never captured - it sits between static and dynamic.
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A transaction in which either all of the database actions occur or none of them do is called:
Answer: A
Correct answer: atomic.
Atomicity is the all-or-nothing property: the transaction either completes in full or leaves the database exactly as it found it. It is the first of the four ACID properties, the others being consistency, isolation and durability. It is what makes a multi-step operation such as a transfer between accounts safe.
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Which of the following occurs when a transaction rereads data it has previously read and finds modification or deletions caused by a committed transaction?
Answer: A
Correct answer: Nonrepeatable read
A non-repeatable read occurs when a transaction reads a row, another transaction modifies or deletes it and commits, and the first transaction reads it again and sees something different. The remedy is the repeatable-read isolation level, which holds read locks to the end of the transaction.
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Which of the following locks the item from access of any type?
Answer: C
Correct answer: Exclusive lock
An exclusive lock excludes everyone else entirely: no other transaction may read the item or change it while the lock is held. It is what a writing transaction needs. A shared lock is the weaker form, permitting concurrent readers but no writer, which is why several may be held on the same item at once.
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The transaction log contains a copy of every database record (or page) after it has changed. These records are called before images.
Answer: B
Correct answer: False
A record of a page after it has changed is an after image; a before image is the copy taken beforehand. Both are kept, and each has its own use in recovery: after images are applied to roll a transaction forward, before images to roll it back.
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