Deck 10: Transaction Management and Concurrency Control

Question 1

A field-level lock allows concurrent transactions to access the same row, as long as they require the use of different fields within that row.

Answer 1

True

Question 2

When using an optimistic approach, during the read phase, a transaction reads the database, executes the needed computations, and makes the updates to a private copy of the database values.

Answer 2

True

Question 3

The multiuser DBMS must implement controls to ensure serializability and isolation of transactions, in addition to atomicity and durability, in order to guard the database's consistency and integrity.

Answer 3

True

Question 4

Time stamping demands a lot of system resources because many transactions might have to be stopped, rescheduled, and restamped.

Question 5

A shared lock produces no conflict as long as all the concurrent transactions are read-write only.

Question 6

The DBMS guarantees that the semantic meaning of a transaction truly represents the real-world event.

Question 7

An optimistic approach is based on the assumption that the majority of the database operations do not conflict.

Question 8

The scheduler establishes the order in which the operations within concurrent transactions are executed.

Question 9

The serializable isolation level is the least restrictive level defined by the ANSI SQL standard.

Question 10

A lock guarantees the open use of a data item to multiple transactions.

Question 11

Serializability means that data used during the execution of a transaction cannot be used by a second transaction until the first one is completed.

Question 12

The phenomenon of uncommitted data occurs when two transactions are executed concurrently and the first transaction is rolled back after the second transaction has already accessed the uncommitted data-thus violating the isolation property of transactions.

Question 13

Although the DBMS is designed to recover a database to a previous consistent state when an interruption prevents the completion of a required set of transactions, the transactions themselves are defined by the end user or programmer and must be semantically correct.

Question 14

Atomicity indicates the permanence of the database's consistent state.

Question 15

Durability requires that all portions of the transaction must be treated as a single, logical unit of work in which all operations are applied and completed to produce a consistent database.

Question 16

A scheduler facilitates data isolation to ensure that two transactions do not update the same data element at the same time.

Question 17

Most real-world database transactions are formed by only one database request.

Question 18

In a page-level lock, the DBMS will lock an entire diskpage.

Question 19

Time stamps must only have the single property of uniqueness.

Question 20

A growing phase in a two-phase lock is when a transaction acquires all the required locks without locking any data.

Question 21

A consistent database state is one in which all _____.

A) tables have foreign keys
B) data integrity constraints are satisfied
C) table are normalized
D) SQL statements only update one table at a time

Question 22

ANSI has defined standards that govern SQL database transactions. Transaction support is provided by two SQL statements _____ and ROLLBACK.

A) RETRIEVE
B) ASSIGN
C) UPDATE
D) COMMIT

Question 23

The information stored in the _____ is used by the DBMS for a recovery requirement triggered by a ROLLBACK statement, a program's abnormal termination, or a system failure such as a network discrepancy or a disk crash.

A) data dictionary 
B) metadata
C) rollback manager
D) transaction log

Question 24

_____ requires that all operations of a transaction be completed.

A) Specificity
B) Atomicity
C) Durability
D) Time stamping

Question 25

_____ are required to prevent another transaction form reading inconsistent data.

A) Locks
B) Schedules
C) Stamps
D) Logs

Question 26

Of the following events, which is defined by ANSI as being equivalent to a COMMIT?

A) Five SQL statements are executed.
B) The end of a program is successfully reached.
C) The program is abnormally terminated.
D) The database is shut down for  maintenance.

Question 27

One of the three most common data integrity and consistency problems is _____.

A) lost updates
B) disk failures
C) user errors 
D) deadlocks

Question 28

_____ means that data used during the execution of a transaction cannot be used by a second transaction until the first one is completed.

A) Serializability 
B) Atomicity
C) Isolation
D) Time stamping

Question 29

A single-user database system automatically ensures_____ of the database, because only one transaction is executed at a time.

A) serializability and durability 
B) atomicity and isolation
C) serializability and isolation
D) atomicity and serializability

Question 30

As long as two transactions, T1 and T2, access _____ data, there is no conflict, and the order of execution is irrelevant to the final outcome.

A) shared
B) common
C) unrelated
D) locked

Question 31

A _____ lock will lock the entire table, preventing access to any row by a transaction while another transaction is using the table.

A) database-level
B) table-level
C) page-level
D) row-level

Question 32

A _____ lock allows concurrent transactions to access different rows of the same table.

A) database table
B) table-level
C) page-level
D) row-level

Question 33

_____ occurs when a transaction accesses data before and after one or more other transactions finish working with such data.

A) Inconsistent retrieval 
B) The phenomena of uncommitted data
C) Lost update problems
D) Dirty read problems

Question 34

Of the following events, which is defined by ANSI as being equivalent to a ROLLBACK?

A) Five SQL statements are executed.
B) The end of a program is successfully reached.
C) All changes are aborted and returned to a previous consistent state.
D) The database is shut down for maintenance.

Question 35

The implicit beginning of a transaction is when _____.

A) a database is started
B) a table is accessed for the first time
C) the first SQL statement is encountered
D) the COMMIT command is issued

Question 36

Transaction is a _____ unit of work that must be either entirely completed or aborted.

A) time
B) practical
C) logical
D) physical

Question 37

The _____ manager is responsible for assigning and policing the locks used by transactions.

A) transaction
B) database
C) lock
D) schedule

Question 38

A _____ lock will lock the entire diskpage.

A) transaction-level
B) table-level
C) page-level
D) row-level

Question 39

A diskpage, or page, is the equivalent of a _____.

A) database table
B) disk sector
C) database schema
D) diskblock

Question 40

Lock _____ indicates the level of lock use.

A) granularity
B) shrinking
C) growing
D) serializability

Question 41

A(n) _____ lock exists when concurrent transactions are granted read access on the basis of a common lock.

A) shared 
B) exclusive
C) binary
D) two-phase

Question 42

To determine the appropriate order of the operations, the scheduler bases its actions on concurrency control algorithms, such as _____ or time stamping methods.

Question 43

_____ can take place at any of the following levels: database, table, page, row, or field.

Question 44

A(n) _____ specifically reserves access to the transaction that locked the object.

A) shared lock
B) exclusive lock
C) binary lock
D) deadlock

Question 45

The _____ occurs when two concurrent transactions, T1 and T2, are updating the same data element and one of the updates is lost.

Question 46

In the optimistic approach, during the _____ phase, changes are permanently applied to the database.

A) read
B) validation
C) write
D) shared

Question 47

Although the DBMS is designed to recover a database to a previous consistent state when an interruption prevents the completion of a required set of transactions, the transactions themselves are defined by the end user or programmer and must be _____ correct.

Question 48

A(n) _____ condition occurs when two or more transactions wait for each other to unlock data.

A) deadlock
B) exclusive lock
C) binary lock
D) two-phase lock

Question 49

A(n) _____ phase in a two phase lock is when a transaction releases all locks and cannot obtain a new lock.

A) growing
B) shrinking
C) locking
D) unlocking

Question 50

In the wait/die scheme, the:

A) older transaction rolls back the younger transaction and reschedules it.
B) younger, preempted transaction is rescheduled using the same time stamp.
C) older transaction waits for the younger one to complete and release its locks.
D) younger and older transactions both wait indefinitely to be released.

Question 51

Most multiuser _____ automatically initiate and enforce locking procedures, where all locking information is managed by the lock manager.

Question 52

The _____ isolation level ensures that queries return consistent results.

A) read uncommitted
B) read committed
C) serializable
D) repeatable read

Question 53

What rule applies to the two-phase locking protocol?

A) Two transactions cannot have conflicting lock.
B) No unlock operation can precede a lock operation in a different transaction.
C) No data is affected until all locks are released.
D) No data is affected until the transaction is in its locked position.

Question 54

_____-level locks are less restrictive than database-level locks, but they create traffic jams when many transactions are waiting to access the same table.

Question 55

The _____ interleaves the execution of database operations to ensure serializability.

Question 56

In the optimistic approach, during the_____ phase, a transaction scans the database, executes the needed computations, and makes the updates to a private copy of the database values.

A) read
B) validation
C) write
D) shared

Question 57

The objective of _____ control is to ensure the serializability of transactions in a multiuser database environment.

Question 58

The scheduler's main job is to create a(n) _____ of a transaction's operation, in which the interleaved executions of transactions yield the same results as if the transactions were executed in serial order.

Question 59

If a(n) _____ is issued before the termination of a transaction, the DBMS will restore the database only for that particular transaction, rather than for all transactions, in order to maintain the durability of the previous transactions.

Question 60

The _____ approach to scheduling concurrent transactions assigns a global unique stamp to each transaction.

A) scheduled
B) table-locking
C) unique
D) time stamping 

Question 61

Database transaction _____ restores a database from an inconsistent state to a previously consistent state.

Question 62

A(n) ______ occurs when a transaction executes a query at time T1, and it runs the same query at same time T2, yielding additional rows that satisfy the query.

Question 63

In a heavily used database management system (DBMS), the prevention and detection of _____ constitutes an important DBMS function.

Question 64

What are database checkpoints?

Question 65

The _____ rule states that only one transaction at a time can own an exclusive lock on the same object.

Question 66

The DBMS uses the information stored in the _____log for a recovery requirement triggered by a ROLLBACK statement, a program's abnormal termination, or a system failure such as a network discrepancy or a disk crash.

Question 67

What are the three basic techniques to control deadlocks?

Question 68

As a rule, a(n) _____ must unlock the object after its termination.

Question 69

What is transaction isolation and why it is important?

Question 70

_____ ensure that a disk physical failure will not impair the DBMS's ability to recover data.

Question 71

If T1 has not unlocked data item Y, T2 cannot begin; if T2 has not unlocked data item X, T1 cannot continue. Consequently, T1 and T2 each wait for the other to unlock the required data item. Such a deadlock is also known as a(n) _____.

Question 72

Uniqueness ensures that no equal time stamp values can exist, and _____ ensures that time stamp values always increase.

Question 73

The _____ protocol ensures that transaction logs are always written before any database data is actually updated.

Question 74

How does a shared/exclusive lock schema increase the lock manager's overhead?