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UGC NET CSE | December 2014 | Part 3 | Question: 08

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Which of the following is correct ?

I. Two phase locking is an optimistic protocol.

II. Two phase locking is pessimistic protocol

III. Time stamping is an optimistic protocol.

IV. Time stamping is pessimistic protocol. 

  1. $I$ and $III$
  2. $II$ and $IV$
  3. $I$ and $IV$ 
  4. $II$ and $III$ 
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ans will be B
This validation scheme is called the optimistic concurrency-control scheme since transactions execute optimistically, assuming they will be able to finish execution and validate at the end.

In contrast, locking and timestamp ordering are pessimistic in that they force a wait or a rollback whenever a conflict is detected,
even though there is a chance that the schedule may be conflict serializable.  
Korth pg 689                            
In optimistic concurrency control techniques, also known as validation or certification techniques, no checking is done while the transaction is executing. Several proposed concurrency control methods use the validation technique

navathe pg 608
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