GATE Overflow Test Series | Mixed Subjects | Test 3 | Question: 10

Question

Which of the following statements is/are correct? (Mark all the appropriate choices)

• A. With strict $\text{2PL,}$ transactions can be serialized in the order in which they commit
• B. Strict $\text{2PL,}$ holds only exclusive locks until the end of the transaction
• C. Rigorous $\text{2PL,}$ holds both shared and exclusive locks until the end of the transaction
• D. With rigorous $\text{2PL,}$ transactions can be serialized in the order in which they commit

Comments

I feel option A must also be correct, with strict 2pl transaction a can be serializable in the order of commit and also in the order of lock point it depends on the scenario.
1.At the order of lock-point if:- we do all read operations followed by all write operations.
2.At the order of commit:- If we do all write operations followed by all read operations.

Answer 1

With rigorous $\text{2PL,}$ locks are released only at the end of the transaction. It can be shown that with rigorous $\text{2PL,}$ transactions can be serialized in the order in which they commit.

Strict $\text{2PL,}$ holds only exclusive locks until the end of the transaction.

So, only options $B; C;D$ are TRUE.

Comments

@KineticKarm

With Strict 2PL , transactions can ALWAYS be serialized in order in which they commit,

Then Option A should also be correct which says, With Strict 2PL, transactions CAN be serialized in order in which they commit. 

I am not getting the difference between these two. 

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@Arpit Patel I have edited comment. I want to say given option-A is correct but if we put ALWAYS then it will be false.

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@GO Classes, @Sachin Mittal 1 sir,  @gatecse we use concept of locking point to serialize transactions, then how option D is correct?