Deck 13: Managing Transactions and Concurrency

Question 1

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

Answer 1

False

Question 2

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.

Answer 2

True

Question 3

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

Answer 3

False

Question 4

The last step in the write-through technique recovery procedure is to identify the last checkpoint in the transaction log.

Question 5

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

Question 6

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

Question 7

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

Question 8

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 9

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 10

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 11

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

Question 12

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.

Question 13

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 14

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

Question 15

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

Question 16

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 17

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

Question 18

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

Question 19

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

Question 20

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

Question 21

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

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

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

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 24

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

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

Question 25

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 26

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 27

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 28

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 29

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 30

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

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

Question 31

____ requires that all operations of a transaction be completed.

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

Question 32

A ____ lock locks the entire diskpage.

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

Question 33

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

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

Question 34

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 35

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 36

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 37

____ 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 38

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

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

Question 39

Lock ____ indicates the level of lock use.

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

Question 40

A consistent database state 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 41

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

Question 42

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

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

Question 43

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 44

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

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

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

Question 47

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 48

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

Question 49

____________________-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 50

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

Question 51

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

Question 52

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

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

Question 53

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 54

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 55

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 56

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 57

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

Question 58

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 59

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

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

Question 60

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

A) scheduled
B) table-locking
C) unique
D) timestamping

Question 61

What are the three basic techniques to control deadlocks?

Question 62

What is transaction isolation and why it is important?

Question 63

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 64

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

Question 65

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

Question 66

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

Question 67

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

Question 68

What are database checkpoints?

Question 69

Explain the transaction log. What is its function?

Question 70

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