Doubt in Schedule serialisation in DBMS

Question

is it true that

 if schedule is 2pl(P) then it is  serializable(Q) too

It is mentioned one of in comment of answer https://gateoverflow.in/1484/gate1999-2-6

I don't think so

T1	T2
	Write B (T2 acquire Ex(B))
Write B(T1 not able acquire Ex(B))
	Write A (T2 acquire Ex(A))
Write A(T1 not able acquire Ex(A))
	Write A(T2 already holds Ex(A))

Cleary it is 2PL but not serializable (as there is cycle)

So my question is "Is there any correlation between 2PL and serializability" 

 

 

 

Answer 1

is it true that

 if schedule is 2pl(P) then it is  serializable(Q) too

Yes. If any Schedule is allowed by the 2PL protocol then It is Serializable. 

Refer my answer here : https://gateoverflow.in/223561/self-doubt

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 Cleary it is 2PL but not serializable (as there is cycle)

No, the given schedule is Not allowed by the 2PL protocol. $W_1(B)$ will have to wait until complete $T_2$ is completed. 

Comments

Hi deepak

thank you for such super fast reply.

I have gone through answer you provided in another question

I have some doubt , you said

"No, the given schedule is Not allowed by the 2PL protocol. W1(B) will have to wait until complete T2 is completed".

I agree with you on this . that 2PL will not allow T1 to run. Therefore T2 completes its execution and after T2 releases all locks , now T1 can start running.

Does that means 2PL has done it's job and made non seriaizable schedule serializable

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Also from which book/PDF you referred image , you gave in https://gateoverflow.in/223561/self-doubt?

thank you

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Does that means 2PL has done it's job and made non seriaizable schedule serializable

It means that 2PL did not allow the Original Schedule to run as it is. 

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Also from which book/PDF you referred image , you gave in

From Chegg.com.