Unit 4

Question 1

What is transaction ?

Answer 1

set of operations used to perform a logical unit of work.

Question 2

What is Full form of ACID (properties) ?

Answer 2

Atomicity , Consistency , Isolation , Durability.

Question 3

Meaning of Atomicity in context of Transactions ?

Answer 3

Either all operations are performed or none.

Question 4

Meaning of Consistency in context of Transactions ?

Answer 4

Before and after transaction sum of money should be same. (state of data should should be consistent)

Question 5

Meaning of Isolation in context of Transactions ?

Answer 5

A parallel schedule should be able to converted into serial schedule to achieve consistancy.

Question 6

Meaning of Durability in context of Transactions ?

Answer 6

Changes made in DB should be permanent.

Question 7

What are the operation that are performed in a transaction

Answer 7

1. Read
2. Write
3. Commit
4. Rollback

Question 8

What are states of transaction

Answer 8

1. Active
2. Partially Committed
3. Commited
4. Terminated State : (Involves Resource Deallocation)
5. Failed
6. Abort :

Question 9

What happens in active state ?

Answer 9

The transaction begins and is actively executing operations.
It can read and write in this state
ex. A bank transaction starts by reading your account balance.

Question 10

What happens in partially committed state

Answer 10

Transaction has finished it’s operations, but changes have not yet been parmanently saved (commited) to database.

ex. after removing money from your account and adding to another account , the transaction is ready to be finalized but hasn’t been saved yet.

Question 11

What happens in committed state ?

Answer 11

The transaction is successfully completed, and all changes are permanently saved in the database.

Example: The money transfer is now permanent, and both account balances are updated.

Question 12

What happens in failed state

Answer 12

Something goes wrong during the transaction (e.g., a system crash or a data error).
The transaction cannot proceed to the next step. It goes in failed state.
Example: If there’s a power failure while transferring money, the transaction cannot continue.

Question 13

What happens in aborted state ?

Answer 13

In this state , the transaction is rolled back, undoing any changes made during its active state.

To achieve consistency

Example: If the power failure occurs, the transaction will undo the transfer, returning the account balances to their original amounts.

Question 14

What happens in terminated State ?

Answer 14

This state is achieved when transaction has finished it’s process either by committing or abortion.

Final state where transaction ends.
Example: After either successfully transferring the money or rolling back the changes due to an error, the transaction is considered complete.

Question 15

What is schedule ?

Answer 15

It is chronological execution sequence of multiple transactions

Question 16

What are types of schedule

Answer 16

• Based on Serializability

1. Serial Schedule
2. Parallel Schedule

• Based on Recoverability

1. Recoverable
2. Irrecoverable

Question 17

What is serial Scheduling

Answer 17

In this scheduling execution of one transaction stats only after completion of Other transaction

This scheduling can be carried in controlled way.

Here Database remains consistent by nature

ex. In ATM one user can at a time withdraw money

Question 18

What is parallel transaction

Answer 18

More than one transactions are executed at a time.

Waiting time is less for all transactions. i.e. throughput increases.

Question 19

what is recoverable and irrecoverable schedule

Answer 19

A recoverable schedule in database transaction management ensures that if a transaction needs to be rolled back due to a failure, it doesn’t cause other dependent transactions to be in an inconsistent state.

irrocoverable don’t guarantee consistance after system in between failure

Question 20

Example of recoverable schedule

Answer 20

T1 :R(A)
T1 : A=A+10
T1 : W(A)
T2 : R(A) (Dirty Read)
T2: A=A-5
T2 : W(A)
C : T1
C : T2

Question 21

How to identify if some process is irrecoverable

Answer 21

If one transaction is doing dirty read and the one who is doing dirty read (copying is commited before) then it is irrecoverable otherwise recoverable

Question 22

example of irrecoverable schedule

Answer 22

T1 :R(A)
T1 : A=A+10
T1 : W(A)
T2 : R(A) (Dirty Read)
T2: A=A-5
T2 : W(A)
C : T2
C : T1

Question 23

What is cascade roleback ?

Answer 23

A cascaded rollback occurs when a failure in one transaction causes other transactions, which have read data from the failed transaction, to also be rolled back. This can lead to a chain reaction of rollbacks.

Question 24

What is cascadeless roleback

Answer 24

A cascadeless rollback avoids chain reaction of roleback by ensuring that transactions only read data that has already been committed by other transactions. This way, if a transaction fails and rolls back, it doesn’t affect other transactions.

Question 25

how to achieve cascadelessness

Answer 25

to achieve cascadelessness we have to completely avoid dirty read problem i.e. one transaction only reads when its previous process has commited its transaction

Question 26

When can we say that schedule is conflict serializable

Answer 26

When we swap any non conflicting operations and they became e