Data and Database Administration Questions and Answers

Answer: D

Correct answer: The essential data of the record

A transaction log records the essential data of each transaction: its identifier, the time, the type of action, and the data affected. The before and after images of changed records are held in the database change log, which is what a rollback or rollforward actually replays.

Answer: D

Correct answer: All of the above.

Data may be unavailable for any of the three reasons: it may be lost or inaccurate, the server may be down, or the database may be off-line for planned maintenance. Availability is a matter of the whole system, not of the data alone, which is why maintenance windows are themselves an availability cost.

Answer: C

Correct answer: Read

A shared lock permits reading, and several transactions may hold one on the same item at the same time - reads do not interfere with each other. Any change requires an exclusive lock, which no other transaction may hold in any mode.

Answer: B

Correct answer: Deadlock

Locking prevents interference but creates the possibility of deadlock - each transaction waiting for a lock another holds, in a circle. The system must therefore detect deadlocks and break them by rolling a transaction back, which is the price paid for the safety locking gives.

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.

Answer: A

Correct answer: Rollback

When a single transaction fails part way through, only that transaction’s work needs undoing - so the system applies the before-images from the log and rolls it back. Nothing else in the database is affected, which is why this is far cheaper than any of the alternatives.

Answer: A

Correct answer: Is free or nearly free database software whose source code is publicly available

Open-source means the source code is published and may be inspected, modified and redistributed, and the software is generally free or nearly so. MySQL and PostgreSQL are the familiar database examples, and both are competitive with commercial products and substantially SQL compliant.

Answer: A

Correct answer: To ensure data integrity when updates occur to the database in a multiuser environment

Concurrency control exists because several users may update at once. Reads alone cannot corrupt anything, and with a single user there is no interleaving to control - so it is the combination of updates and multiple users that creates the problem.

Answer: C

Correct answer: Switch to duplicate database

After a system failure the quickest route back to service is to switch to a duplicate - a mirrored or standby database kept in step with the original - so that operations continue while the failed copy is repaired. Rollforward from a backup and log is the fallback where no duplicate exists, and it takes far longer.

Answer: B

Correct answer: The time to make a decision and the typical roles of a database administrator

A data warehouse administrator does everything a database administrator does - storage, backup, tuning, security - and is additionally judged on how fast the warehouse can answer a question, since its whole purpose is to support decisions. A warehouse that is correct but slow has failed at its job.