Translation and Regulation Questions and Answers

Q: Which of the following occurs when a transaction rereads data and finds new rows that were inserted by a committed transaction since the prior read?

Correct answer: Phantom readA phantom read occurs when a transaction repeats a query and finds new rows that another, now committed, transaction inserted. It differs from a non-repeatable read in that rows have appeared, not merely changed - which is why row locks cannot prevent it and only the serialisable isolation level does.

Q: What are the ways of dealing with deadlock?

Correct answer: All of the mentionedThere are three approaches. Prevention designs the system so a deadlock cannot arise - by ordering resources, or by the wait-die and wound-wait schemes. Detection lets deadlocks happen and looks for cycles in the wait-for graph. Recovery then breaks the deadlock by rolling a transaction back.

Q: A transaction that has completed its execution is said to be

Correct answer: CommittedA transaction that has finished and whose changes have been made permanent is committed. Once committed it cannot be rolled back, and durability guarantees the changes will survive a crash.

Q: Selecting the victim to be rolled back to its previous state is determined by the minimum cost. The factors determining the cost of a rollback are

Correct answer: All of the aboveChoosing the victim means choosing the cheapest rollback, and all three factors bear on the cost: how much work would be lost and how much remains, how many data items the transaction has already used, and how many more it needs and how many other transactions the rollback would drag in. A further consideration is how often a transaction has already been rolled back, so that no transaction is starved.

Q: The deadlock state can be changed back to stable state by using _____________ statement.

Correct answer: RollbackA deadlock is broken by choosing a victim and rolling it back, which releases its locks and lets the others continue. The victim is normally chosen as the one that has done least work, and it is usually restarted afterwards.

Q: The application of database management system in air flight seat booking in a way that one seat is accessed by only one clerk for customer reservation is classified as

Correct answer: online transaction processingBooking a seat is OLTP: many short transactions, run interactively, each reading and updating a few records, with the answer needed at once. Locking the seat so that only one clerk can sell it is the isolation such processing requires. The contrast is with OLAP, where a few long queries read a great deal of data and update nothing.

Q: What is the true inducer of the lac operon in Escherichia coli ?

Correct answer: AllolactoseLactose entering the cell is converted by beta-galactosidase into allolactose, and it is allolactose that binds the repressor and releases it from the operator. This is why lactose itself is often called the inducer only loosely.

Q: A transaction that has not completed successfully is called a _______

Correct answer: Aborted transactionA 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.

61.

Which of the following occurs when a transaction rereads data and finds new rows that were inserted by a committed transaction since the prior read?

A.Nonrepeatable read
B.Phantom read
C.Dirty read
D.Consistent read

Answer: B

Correct answer: Phantom read

A phantom read occurs when a transaction repeats a query and finds new rows that another, now committed, transaction inserted. It differs from a non-repeatable read in that rows have appeared, not merely changed - which is why row locks cannot prevent it and only the serialisable isolation level does.

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62.

What are the ways of dealing with deadlock?

A.Deadlock prevention
B.Deadlock recovery
C.Deadlock detection
D.All of the mentioned

Answer: D

Correct answer: All of the mentioned

There are three approaches. Prevention designs the system so a deadlock cannot arise - by ordering resources, or by the wait-die and wound-wait schemes. Detection lets deadlocks happen and looks for cycles in the wait-for graph. Recovery then breaks the deadlock by rolling a transaction back.

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63.

A transaction that has completed its execution is said to be

A.Saved
B.Loaded
C.Rolled
D.Committed

Answer: D

Correct answer: Committed

A transaction that has finished and whose changes have been made permanent is committed. Once committed it cannot be rolled back, and durability guarantees the changes will survive a crash.

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64.

Selecting the victim to be rolled back to its previous state is determined by the minimum cost. The factors determining the cost of a rollback are

A.How long the transaction has computed, and how much longer the transaction will compute before it completes its designated task.
B.How many data items the transaction has used.
C.How many more data items the transaction needs for it to complete and how many transactions will be involved in the rollback.
D.All of the above

Answer: D

Correct answer: All of the above

Choosing the victim means choosing the cheapest rollback, and all three factors bear on the cost: how much work would be lost and how much remains, how many data items the transaction has already used, and how many more it needs and how many other transactions the rollback would drag in. A further consideration is how often a transaction has already been rolled back, so that no transaction is starved.

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65.

The deadlock state can be changed back to stable state by using _____________ statement.

A.Commit
B.Rollback
C.Savepoint
D.Deadlock

Answer: B

Correct answer: Rollback

A deadlock is broken by choosing a victim and rolling it back, which releases its locks and lets the others continue. The victim is normally chosen as the one that has done least work, and it is usually restarted afterwards.

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66.

The application of database management system in air flight seat booking in a way that one seat is accessed by only one clerk for customer reservation is classified as

A.online transaction processing
B.offline transaction processing
C.online logical representation
D.offline modeling representation

Answer: A

Correct answer: online transaction processing

Booking a seat is OLTP: many short transactions, run interactively, each reading and updating a few records, with the answer needed at once. Locking the seat so that only one clerk can sell it is the isolation such processing requires. The contrast is with OLAP, where a few long queries read a great deal of data and update nothing.

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67.

Performance analysis and tuning is which of the following?

A.Undertaken one time at the time of a DBMS installation
B.Undertaken one time at the time of the implementation of a new application
C.Undertaken as an ongoing part of the backup of a database
D.Undertaken as an ongoing part of managing a database

Answer: D

Correct answer: Undertaken as an ongoing part of managing a database

Performance tuning is continuous, not a one-off at installation. Data volumes grow, the mix of queries changes, indexes that once helped become a burden on updates - so a database that was well tuned last year may not be now. Monitoring and adjustment are part of ordinary administration.

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68.

What is the true inducer of the lac operon in Escherichia coli ?

A.Lactose
B.Allolactose
C.Glucose
D.Galactose

Answer: D

Correct answer: Allolactose

Lactose entering the cell is converted by beta-galactosidase into allolactose, and it is allolactose that binds the repressor and releases it from the operator. This is why lactose itself is often called the inducer only loosely.

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69.

The Shine-Dalgarno sequence is

A.trailer sequence
B.a stop codon
C.the reading frame of a gene
D.a short sequence that acts as a ribosomal binding site

Answer: D

Correct answer: a short sequence that acts as a ribosomal binding site

The Shine-Dalgarno sequence is a purine-rich stretch a few bases upstream of the start codon. It base-pairs with a complementary sequence at the 3’ end of the 16S rRNA, which positions the ribosome so that the correct AUG is in the P site. Prokaryotic mRNAs are often polycistronic, and each cistron has its own Shine-Dalgarno sequence.

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70.

A transaction that has not completed successfully is called a _______

A.Compensating transaction
B.Aborted transaction
C.Active transaction
D.Partially committed transaction

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.

Discuss in Forum

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