ISRO-2013-23

Question

Which of the following is the highest isolation level in transaction management?

• A. Serializable
• B. Repeated Read
• C. Committed Read
• D. Uncommitted Read

Answer 1

Answer is Serializable ---Highest isolation level and Lowest one is Read Uncommitted 

The Isolation level are defined for transaction :

We will see what violation can happen with each isolation level : violation are Dirty read , Non repeatable read, Phantom .

The first one is Read Uncommitted : So here Dirty read , Non repeatable read, Phantom . all are possible  

The second One is  Read Committed : It reads the data after the another transaction is committed But it doesnt guarantee That the next time it will read the same data value then it will get same old value .. Dirty read--Not possible  , Non repeatable read--Possible , Phantom-- Possible .

Third one : Repeated Read : : It reads the data after the another transaction is committed But it  guarantee That the next time it will read the same data value then it will get same old value .. Dirty read--Not possible  , Non repeatable read--not possible, Phantom-- Possible .

Fourth One is : Serializable : It is highest and toughest isolation level . It will give always Consistent result . It would have schedules equivalent to Serial Schedules .Dirty read--Not possible  , Non repeatable read--Possible , Phantom-- Not Possible .

 .

Answer 2

Option A is correct here.

Serializable  is the highest isolation level in transaction management.

Source:https://en.wikipedia.org/wiki/Isolation_%28database_systems%29

Answer 3

c) Committed read

Isolation is for concurrency management of DBMS.

And concurrency control violates serializability

https://vladmihalcea.com/2014/12/23/a-beginners-guide-to-transaction-isolation-levels-in-enterprise-java/

Am I correct?

Comments

what about option A.??

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see now.

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somewhat but here highest isolation level means DBMS usually acquires lock on data or implements multiversion concurrency, which may result in a loss of concurrency

serializability requires read and write locks (acquired on selected data) to be released at the end of the transaction. .

But Read commited  keeps write locks  until the end of the transaction, but read locks are released as soon as the operation is performed