Transaction Managment

Question 1

How layers has DBMS have

Answer 1

3

Question 2

The inner most layer ( the kernel ) concerns itself with:

Answer 2

Hardware failure
Software failure
Consistency of the database

Question 3

Transaction management is further subdivided into:

Answer 3

Transaction support
Concurrency control
Database recovery

Question 4

Concurrency and recovery control required:

Answer 4

Are required to protect the database from inconsistencies and data loss

Question 5

Concurrency allow DBMS’s what

Answer 5

Many DBMSs allow users to carry out operations on the database

Question 6

Concurrency , If the operations are not controlled ,what?

Answer 6

database will become inconsistent

Question 7

Recovery, mean
Eg.

Explain

Answer 7

Is the process of restoring the database to a correct state following a failure

Ex. A failure may be a result of:
A system crash
A software error

Whatever the reason, DBMS must be able to recover from the failure and restore the database to a consistent state

Question 8

Consider an application program which processes the sale of stock

Answer 8

Contains a several database operations

Is a read write transaction data is being updated

Question 9

What transaction

Transaction might be what

Answer 9

Is a logical unit of work on the database

Might be :
An entire computer application
A single command such as select , insert , update , delete

Question 10

Transaction outcome

Successful:

Answer 10

Transaction completes successfully

Transaction is said to have committed

Question 11

Transaction unsuccessful

Answer 11

Transaction does not complete successfully

Transaction is aborted

Question 12

SQL COMMIT statement

Answer 12

Statement makes transaction updates permanent

Signifies a successful transaction

If it is decided that a committed transaction was a mistake :
Another transaction to reverse its effects must be performed
Revert to database backup files

Question 13

SQL ROLLBACK statement

Answer 13

Statement undoes any transaction updates made since the start of the transaction

Signifies an unsuccessful transaction

Question 14

Transaction properties

Answer 14

Atomicity
Consistency
Isolation
Durability

Question 15

Reliability and consistency are compromised when:

Answer 15

Software and hardware failures occur

Must be maintained at all times

Question 16

Explain Atomicity

Answer 16

All or nothing property
Either the entire transaction is performed or it is not performed at all

If one operation fails, all must be undone

Question 17

Explain consistency

Answer 17

All transactions must preserve the consistency and integrity of the database.

Question 18

Isolation mean

Answer 18

Transaction execute independently of one another

Question 19

Durability

Answer 19

When transaction completes , the updates made by the transaction must be durable

Question 20

Serialisability mean

Example

Answer 20

Ensures that concurrent execution of several transactions yields consistent results

Ex. T1 = T2 = T3 = result
T2 = T3 = T1 = result
T3 = T2 = T1 = result

Question 21

What are high level database modules of DBMS Architecture (4)

Answer 21

Transaction
Concurrency
Recovery
Control

Question 22

Transaction manager

Answer 22

It communicates with the scheduler, the module responsible for implementing a particular strategy for concurrency control

Question 23

Recovery manager

Answer 23

Ensure that the database is restored to the state it was in at the start of the transaction

Question 24

Buffer manager

Answer 24

Is responsible for the transfer of data between disk storage and main memory

Question 25

Concurrency control

Answer 25

Is a process of managing simultaneous operations on the database without having them interfere with each other

Question 26

What are the three potential problems caused by concurrency

Answer 26

Lost update Uncommitted dependency Inconsistent analysis

Question 27

Explain lost update problem

Answer 27

Successfully completed update operation by one transaction can be overridden by another transaction

Question 28

Lost update, how can we prevent this update from being lost?

Answer 28

The loss of T2s update could be avoided by preventing T1 from reading the account balance until after T2s update has been completed

Question 29

Uncommitted dependency problem

Answer 29

occurs when one transaction is allowed to see the results of another transaction before it has committed

Question 30

Inconsistent analysis problem

Answer 30

Occurs when a transaction reads several values but a second transaction updates some of them during the execution of the first transaction Transactions that only read the database can also sometimes produce inconsistent

Question 31

Serialisability means

Answer 31

Is a means of identifying those transactions which are guaranteed to ensure consistency

Question 32

Schedule

Answer 32

A transaction consists of a sequence of reads and writes to the database

Question 33

Serial Schedule

Answer 33

Schedule where the operations of each transaction are executed consecutively without any operations from other transactions

Question 34

Nonserial schedule

Answer 34

A schedule where the operations from a set of concurrent transactions are interleaved

Question 35

Transaction log

Answer 35

transaction log is a sequential record of all changes made to the database while the actual data is contained in a separate file.

Question 36

Relational data model

Answer 36

Nb