Sunday, December 12, 2021

DBMS MCQ - System crash and the state of a transaction

Multiple choices questions in DBMS, Transaction states in database, What will go wrong to a transaction in case a system crash happens during its execution? Aborted, partially committed, committed and active states of transaction. What are the different possibilities that lead a transaction to fail?

DBMS MCQ - System crash and state of a transaction

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7. Consider the transaction T1 as given below; T1 enters into which of the following states if there is a system crash after the instruction 5?

T1

1

2

3

4

5

6

7

8

Begin_transaction

Read(A)

A:=A-500;

Write(A);

Read(B)

B:=B+500;

Write(B);

Commit;

 

a) Partially committed

b) Committed

c) Aborted

d) Failed

Answer: (d) Failed

A transaction enters into FAILED state if the transaction cannot be committed or the transaction is aborted while in the ACTIVE state, perhaps due to the user aborting the transaction or as a result of system failures (system crash, transaction errors, disk failures etc.) or as a result of the concurrency control protocol aborting the transaction to ensure serializability.

The transaction at FAILED state is rolled back to undo the changes made to the data items and ABORTED.

Transaction states

Active - if a transaction starts its execution it is said to be in active state

Partially committed - if a transaction successfully executed it last statement

Committed - if a transaction successfully executed commit statement.

Failed - if a transaction is not able to proceed for various reasons (refer above)

Aborted - if a transaction reached a failed state, then it will be aborted.

 



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What will happen to a transaction if a system crash has occurred during its execution?

List down different situations that lead a transaction to fail

What are the possible causes that make a transaction to fail its execution?

Different states of transactions in dbms

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