Question

For the system given in figure 3 identify if schedule 2 is conflict equivalent and view equivalent
to schedule 1. Give proper reasons for you answer.
Resolve the issues in schedule 2 by adopting appropriate locking scheme and
apply deadlock prevention scheme to ensure prevention of deadlocks and starvation. (7)

Table 2:Serial Schedule 1
T1   T2   T3   T4   T5
               Read(X)
               Read(Z)
               Read(Y)
               Write(Z)
               Write(Y)
               Write(Z)
   Read(Y)          
   Read(Z)          
Read(Y)              
Read(X)              
       Write(Y)      
       Write(Z)      
       Write(W)      
           Read(W)  
              

Table 3:Schedule 2
T1   T2   T3   T4   T5
               Read(X)
   Read(Y)          
Read(Y)              
       Write(Y)      
       Write(Z)      
               Read(Z)
   Read(Z)          
Read(X)              
           Read(W)  
       Write(W)      
               Read(Y)
               Write(Z)
               Write(Y)
               Write(X)

Figure 3

⦁   In Figure 4 we show the log as it appears at three instances of time.
⦁   Show all the recovery actions in all three cases. (3)
< T0 Start>
<T0,A, 1000, 500>
<T0,B, 2000, 2500>
< T1 Start>
<T1,C, 2000,1500>
<T2 Start>
<T1,D, 3000,3500>
<T3 Start>
< T0 Commit>
<T2,F,400,300>
<T1,C, 1500,1250>
< T2,F,250,350>
<T1,A, 500,750>
< T1 Commit>
      

Answer 1

Step 1 :-

Schedule 1 is Conflict serializwble while schedule 2 is not conflict serializable because there is a cycle between T3 and T2 while for schedule 1 there is no cycle

There is conflict between Read -Write and write -read between T2 and T3 and T3 and T2 in schedule 2while its not happening in schedule 1

So, schedule 2 is not econflict equivalent to schedule 1

Step 2 :- we know that if the schedule is conflict serializable then it is also view serializable so need of checking view serializable for schedule 1

Step 3:-

Now we check view serializable for schedule 2

Case1 Initial read for item X,Y and X ilin schedule is T5

While for schedule 2 initial read for item X,Y and Z is T5,T2 and no intial read for z

In both schedule intial read is different so need to check for final write and updated read

We can conclude that schedule 2 is also not view equivalent to schedule 1

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