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I)All schedules that are allowed under 2PL are also allowed under Timestamp?? Is vice versa true??

II)Plz explain by giving example. I have read that there are schedules that are allowed under 2PL but not under Timestamp and vice versa, but need example. For schdeules allowed under timestamp but not under 2PL is understable bcoz of view serializable nature of timestamp, but how a 2PL schedule not allowed under testamp??

III) Are there conflict serializable schedules that are not allowed under 2PL?? are there any conflict serializable schedule that are not allowed in Timestamp???

IV) Are all view serializable allowed under Timestamp(Thomas write rule)???

Explanation along with example would be helpful.
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1. There  are some schedules which are possible under basic timestamp but not under 2PL and vice-versa.

2. Lets take an example tp prove the first statement.

   Let, TS(T1) = 20   and TS(T2) = 30

   Let, the schedule be:

T1 T2
  W(A)
R(A)  

    

Now, lets see if this possible under basic timestmp protocol.

W(A) of T2 updates the Write-TS(A) = 30 initially.

Then, T1 requests R(A). 

Now, TS(T1) < Write-TS(A)   and hence, T1 read operation is rejected and T1 is rolled back.

But, this schedule is easily possible under 2PL.

Now, the schedule possible under basic timestamp but not under 2PL: TS(T1) = 20, TS(T2) = 30

T1 T2
W(A)  
  R(A)
R(B)  

3. One ssuch schedule which is conflict serializable but not possible with 2PL is:

T1 T2
W(A)  
  R(A)
R(A)  

4.    

2PL scheules $\subseteq$ conflict serializable schedules $\subseteq$ view serializable schedules

Some timestamp schedules that use Thomas' write rule are view serializable but not conflict serializable.

REF: here

    

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