Managing Multiuser Databases Questions and Answers

Q: Which of the following refers to a cursor type where changes of any type and from any source are visible?

Correct answer: DynamicA dynamic cursor shows everything: changes, insertions and deletions from any source, made at any time. It is the most current view and correspondingly the most expensive, since the recordset must be re-evaluated as it is traversed. A static cursor is the opposite extreme, showing a snapshot fixed when the cursor was opened.

Q: Resource locking is a process to prevent multiple applications from obtaining copies of the same record when the record is about to be changed.

Correct answer: TrueResource locking is exactly this: preventing two applications from working on their own copies of the same record and each writing back a result computed from a value the other has already superseded. Without it the second write silently overwrites the first, which is the lost update problem.

Q: An exclusive lock locks the item from change but not from read.

Correct answer: FalseThat describes a shared lock, which permits others to read but not to change. An exclusive lock excludes access of every kind, reading included, which is what a writing transaction requires. Several shared locks may be held on one item at once; an exclusive lock may not coexist with any other.

Q: Which of the following allows dirty reads, nonrepeatable reads and phantom reads to occur?

Correct answer: Read uncommittedRead uncommitted is the weakest level and prevents nothing: dirty reads, nonrepeatable reads and phantoms are all possible, because the transaction takes no read locks and respects none. It is used only where speed matters more than accuracy - an approximate count over a large table, for instance.

Q: The size of a lock is called:

Correct answer: lock granularity.Granularity is the size of the thing locked - a row, a page, a table, or the whole database. It is a trade: a coarse lock is cheap to manage but blocks many transactions, while a fine one allows far more concurrency at the cost of a great many locks to track. The DBMS may escalate from fine to coarse when the count grows.

Q: In optimistic locking, the assumption is made that conflict will occur.

Correct answer: FalseOptimistic locking assumes conflict will not occur: the transaction proceeds without locks and checks at the end whether anything it relied on has changed, rolling back and retrying if so. Pessimistic locking makes the opposite assumption and takes locks before the work begins.

Q: Database administration refers to a function that applies to the entire organization.

Correct answer: FalseThe 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.

Q: A durable transaction is one in which all committed changes are permanent.

Correct answer: TrueDurability 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.

Q: When one transaction reads a changed record that has not been committed to the database a filthy read occurs.

Correct answer: FalseThe 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.

Q: Dirty read, nonrepeatable, and phantom reads are not possible in this instance.

Correct answer: SerializableSerializable 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.

31.

Which of the following refers to a cursor type where changes of any type and from any source are visible?

A.Forward only
B.Static
C.Keyset
D.Dynamic

Answer: D

Correct answer: Dynamic

A dynamic cursor shows everything: changes, insertions and deletions from any source, made at any time. It is the most current view and correspondingly the most expensive, since the recordset must be re-evaluated as it is traversed. A static cursor is the opposite extreme, showing a snapshot fixed when the cursor was opened.

Discuss in Forum

32.

Resource locking is a process to prevent multiple applications from obtaining copies of the same record when the record is about to be changed.

A.True
B.False

Answer: A

Correct answer: True

Resource locking is exactly this: preventing two applications from working on their own copies of the same record and each writing back a result computed from a value the other has already superseded. Without it the second write silently overwrites the first, which is the lost update problem.

Discuss in Forum

33.

An exclusive lock locks the item from change but not from read.

A.True
B.False

Answer: B

Correct answer: False

That describes a shared lock, which permits others to read but not to change. An exclusive lock excludes access of every kind, reading included, which is what a writing transaction requires. Several shared locks may be held on one item at once; an exclusive lock may not coexist with any other.

Discuss in Forum

34.

Which of the following allows dirty reads, nonrepeatable reads and phantom reads to occur?

A.Read committed
B.Read uncommitted
C.Repeatable read
D.Serializable

Answer: B

Correct answer: Read uncommitted

Read uncommitted is the weakest level and prevents nothing: dirty reads, nonrepeatable reads and phantoms are all possible, because the transaction takes no read locks and respects none. It is used only where speed matters more than accuracy - an approximate count over a large table, for instance.

Discuss in Forum

35.

The size of a lock is called:

A.implicit lock.
B.lock granularity.
C.exclusive lock.
D.shared lock.

Answer: B

Correct answer: lock granularity.

Granularity is the size of the thing locked - a row, a page, a table, or the whole database. It is a trade: a coarse lock is cheap to manage but blocks many transactions, while a fine one allows far more concurrency at the cost of a great many locks to track. The DBMS may escalate from fine to coarse when the count grows.

Discuss in Forum

36.

In optimistic locking, the assumption is made that conflict will occur.

A.True
B.False

Answer: B

Correct answer: False

Optimistic locking assumes conflict will not occur: the transaction proceeds without locks and checks at the end whether anything it relied on has changed, rolling back and retrying if so. Pessimistic locking makes the opposite assumption and takes locks before the work begins.

Discuss in Forum

37.

Database administration refers to a function that applies to the entire organization.

A.True
B.False

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.

Discuss in Forum

38.

A durable transaction is one in which all committed changes are permanent.

A.True
B.False

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.

Discuss in Forum

39.

When one transaction reads a changed record that has not been committed to the database a filthy read occurs.

A.True
B.False

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.

Discuss in Forum

40.

Dirty read, nonrepeatable, and phantom reads are not possible in this instance.

A.Read committed
B.Read uncommitted
C.Repeatable read
D.Serializable

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.

Discuss in Forum

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