Consider the following tree for data items (A, B, C, D, E, F, G)

Consider the following tree for data items (A, B, C, D, E, F, G). Check whether the given schedule S is serializable or not?

 

T1

T2

T3

Lock - A

   

Lock - B

   

Lock - D

   

Unlock - B

   
 

Lock - B

 
   

Lock - E

Unlock - D

   

Lock - C

 

Lock - F

Unlock - A

   

Unlock - C

 

Lock - G

   

Unlock - E

 

Lock - E

 
   

Unlock - F

 

Unlock - B

 
   

Unlock - G

 

Unlock - E

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(A) Serializable
(B) Not Serializable
(C) Data insufficient
(D) None

Answer

Discuss

1Comment
Habib Mohammad Khan @habibkhan
25 Aug 2016 05:37 pm

In this question basically ,we have to check whether the schedule is operating fine considering the constraints in Graph - based protocol of concurrency control techniques.

So few things to keep in mind:

1)Here we consider only exclusive locks.

2)First lock can be obtained on any data item on a given transaction of a schedule.Here we need not follow the access sequence shown by database graph.

3)Subsequent locks can be obtained only if immediate parent is locked.

4).Unlocking can be done at any point of time.

5) A transaction is allowed to access a data item atmost once and hence we can say no relocking of same data item is allowed in same transaction.

The above schedule satisfies all the conditions considering the given database graph.

Hence A) should be the correct option.