Locks placed by the DBMS are explicit locks.
Answer: B
Correct answer: False
Locks placed by the DBMS itself are implicit; explicit locks are those the application requests by command. Getting the pair the right way round matters, because most locking in a well-written application is implicit - the developer declares an isolation level and the DBMS places whatever locks are needed to honour it.
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The goal of database security is to ensure that only authorized users can perform authorized activities at authorized times.
Answer: A
Correct answer: True
All three qualifications are needed. Authorised users, so that identity is established; authorised activities, so that a user may read what they may not change; and authorised times, since access appropriate during a shift may not be appropriate outside it. Authentication establishes the first and authorisation the other two.
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Which of the following refers to a cursor type where changes of any type and from any source are visible?
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.
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Resource locking is a process to prevent multiple applications from obtaining copies of the same record when the record is about to be changed.
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on their own copies of the same record and each writing back a result computed from a value the other has already superseded.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.
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An exclusive lock locks the item from change but not from read.
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.
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Which of the following allows dirty reads, nonrepeatable reads and phantom reads to occur?
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.
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The size of a lock is called:
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.
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In optimistic locking, the assumption is made that conflict will occur.
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.
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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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