Question

1. Transactions. Consider an ATM system.

We have 2 transactions. T1: withdraw $50 and T2: withdraw $100. We consider concurrent executions of the transactions. Which schedule(s) is (are) serializable? Explain why.

1. T2 reads the balance.

T1 reads the balance.

T2 withdraw $100.

T1 withdraw $50.

2. T2 reads the balance.

T2 withdraw $100.

T1 reads the balance.

T1 withdraw $50.

3. T2 reads the balance.

T1 reads the balance.

T2 withdraw $100.

T1 withdraw $50.

Answer 1

to check for the serializability one must draw a precedense graph of transaction and check if there is any loop in graph the it is not serializable .

the graph contain vertex as no of different transaction and edges are drawn if any conflicts are found .

various conflicts are :

1] read -write

2] write- read

3] write-write

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for drawing vertex stand in one coloumn and find the conflict in another coloumn and if found draw a vertex. dont found conflict in same coloumn.