The “all-or-none” property is commonly referred to as _________
Answer: C
Correct answer: Atomicity
Atomicity is the all-or-nothing property: a transaction either completes in full or has no effect at all. If it fails part way through, everything it has done is rolled back - which is what stops money being debited from one account and never credited to the other.
Please log in or register to report this question.
Which of the following is a property of transactions?
Answer: D
Correct answer: All of the mentioned
Atomicity, Isolation and Durability are all transaction properties, and with Consistency they make up ACID. Together they let an application treat a group of operations as if it were the only one running and as if it could not fail part way.
Please log in or register to report this question.
Execution of a transaction in isolation preserves the _________ of a database
Answer: B
Correct answer: Consistency
Isolation exists to preserve consistency: if each transaction taken alone leaves the database valid, then running them so that none sees another’s intermediate state leaves it valid too. Without isolation, two individually correct transactions can interleave to produce an incorrect result - two withdrawals both reading the same balance, for instance.
Please log in or register to report this question.
Which of the following is not a property of a transaction?
Answer: B
Correct answer: Simplicity
Simplicity is not a transaction property. The four are Atomicity, Consistency, Isolation and Durability - ACID - and they are guarantees the system makes, not qualities of the code.
Please log in or register to report this question.
Which of the following systems is responsible for ensuring durability?
Answer: A
Correct answer: Recovery system
Durability is the recovery system’s responsibility. It writes changes to a log on stable storage before acknowledging a commit, and after a crash it replays committed transactions and undoes uncommitted ones, so that the database returns to a state reflecting exactly the transactions that had committed.
Please log in or register to report this question.
Which of the following systems is responsible for ensuring isolation?
Answer: C
Correct answer: Concurrency control system
Isolation is the concurrency control system’s responsibility. By locking, timestamping or multiversioning, it ensures that concurrent transactions produce the same result as some serial order of them - so no transaction sees another’s partial work.
Please log in or register to report this question.
State true or false: Information residing in the volatile storage does not usually survive system crashes
Answer: A
Correct answer: True
Volatile storage - main memory and cache - loses its contents when power fails or the system crashes. That is precisely why durability requires writing to non-volatile storage: the log must reach disk before a commit can be reported, or a committed transaction could vanish.
Please log in or register to report this question.
A transaction that has not completed successfully is called a _______
Answer: B
Correct answer: Aborted transaction
A transaction that cannot complete is aborted: everything it has done is rolled back, so the database is left as if it had never begun. That is atomicity in action. A compensating transaction is a different thing - one that undoes the effect of an already committed transaction by applying opposite operations.
Please log in or register to report this question.
Which of the following is not a transaction state?
Answer: D
Correct answer: Compensated
The states of a transaction are active, partially committed, failed, aborted and committed. There is no “compensated” state - a compensating transaction is a separate transaction run afterwards, not a state of the original.
Please log in or register to report this question.
The execution sequences in concurrency control are termed as ________
Answer: B
Correct answer: Schedules
A schedule is the order in which the operations of several concurrent transactions are actually executed. The object of concurrency control is to allow only schedules that are serialisable - equivalent in effect to some serial ordering of the same transactions.
Please log in or register to report this question.
