Transaction & Concurrency control

Question

Which of the following statement is/are incorrect? 
A: A schedule following strict two phase locking protocol is conflict serializable as well as recoverable.
B: Checkpoint in schedules are inserted to ensure recoverability.

(A) Only 1

(B) Only 2

(C) Both 1 and 2

(D) None

 

Comments

only B) is incorrect according to me..

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Yeah.. You are right but checkpoints are useful in recoverability.

Where i'm wrong??

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https://www.gateoverflow.in/234808/self-doubt?show=234858#c234858

check this, may it help to you

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The explanation given is

Checkpoints are inserted to minimize the task of undo-redo in recoverability

So option B is incorrect.

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Verma Ashish

If X ensures recoverability it means that during a system crash Xwill guarantee that all the operations that have been performed till the point of crash will be maintained in the dB or maybe saved somewhere in log files so that it can be later used.

Here if you relate X with checkpoint then you will see that the task of checkpoint is not so.

If you know about deferred and immediate database modification we will see that there we have to undo and redo for so many times in case of system crash. This is not what we want. Checkpoints just avoid that headache for redoing and undoing to some extent if not full.   

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Thanks.

I'm not getting the correct meaning of "ensures recoverability". Now it is clear.  :)

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It's like when you break your leg ice acts as a temporary pain "reducing" solution but only doctor + plaster can recover that crack and heal the pain :v :p  If you don't apply ice(here checkpoint) then you will have to bear the pain for a longer time but it doesn't help in "curing" the damage

Answer 1

Statement A is true because strict 2 PL ensure serializibility and recoveribility .

Statement B is false because checkpoints are used for minimize redo-undo operation.it is not ensure recoveribility.