Deck 10: Transaction Management and Concurrency Control

Question 1

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

Answer 1

False

Question 2

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 2

True

Question 3

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

Answer 3

False

Question 4

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

Question 5

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

Question 6

When you read from or update a database,you create a transaction.

Question 7

Incomplete or improper transactions can have a devastating effect on database integrity.

Question 8

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

Question 9

To ensure consistency of the database,every transaction must begin with the database in an unstable state.

Question 10

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

Question 11

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

Question 12

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

Question 13

When using an optimistic approach,during the write phase,the transaction is validated to ensure that the changes made will not affect the integrity and consistency of the database.

Question 14

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 15

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 16

The transaction recovery write-ahead-log protocol ensures that transaction logs are always written before any database data are actually updated.

Question 17

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

Question 18

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.

Question 19

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 20

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 21

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 22

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 23

____ requires that all operations of a transaction be completed.

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

Question 24

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

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

Question 25

The 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 26

A consistent database is ____.

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

Question 27

A ____ lock locks the entire diskpage.

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

Question 28

ANSI defines four events that signal the end of a transaction.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) The program is abnormally terminated.
D) The database is shut down for maintenance.

Question 29

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 30

____ are required to prevent another transaction from reading inconsistent data.

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

Question 31

All transactions must display ____.

A) atomicity,consistency,and durability
B) durability and isolation
C) consistency,durability,and isolation
D) atomicity,durability,consistency,and isolation

Question 32

Lock ____ indicates the level of lock use.

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

Question 33

ANSI defines four events that signal the end of a transaction.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 34

The implicit beginning of a transaction is ____.

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

Question 35

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

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

Question 36

____ 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 37

A transaction is a ____ unit of work that must be either entirely completed or aborted.

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

Question 38

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

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

Question 39

A ____ lock prevents the use of any tables in the database from one transaction while another transaction is being processed.

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

Question 40

A ____ lock locks 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 41

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 42

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

Question 43

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

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

Question 44

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

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

Question 45

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 46

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

Question 47

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

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

Question 48

What is a rule that applies to the two-phase locking protocol?

A) Two transactions cannot have conflicting locks.
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 49

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

Question 50

____________________ control is important because the simultaneous execution of transactions over a shared database can create several data integrity and consistency problems.

Question 51

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 52

A(n)____ lock has only two stages (0 and 1).

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

Question 53

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 54

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

Question 55

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

Question 56

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 57

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

Question 58

During the ____ phase,changes are permanently applied to the database.

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

Question 59

____________________-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 60

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 61

What are the three basic techniques to control deadlocks?

Question 62

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

Question 63

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

Question 64

What are database checkpoints?

Question 65

Explain the transaction log.What is its function?

Question 66

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 67

What is transaction isolation and why it is important?

Question 68

The DBMS keeps several copies of ____________________ to ensure that a disk physical failure will not impair the DBMS's ability to recover data.

Question 69

Explain the functions of shared and exclusive locks.

Question 70

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