The operation create inserts a new bank account at a branch. The transactions T and U are defined as follows:

Question

T: aBranch.create("Z");

U: z.deposit(10); z.deposit(20).



Assume that Z does not yet exist. Assume also that the deposit operation does nothing if the account given as argument does not exist. Consider the following interleaving of transactions T and U:



State the balance of Z after their execution in this order. Are these consistent with serially equivalent executions of T and U?

Answer 1

In the example, Z’s balance is $20 at the end. Serial executions of T and U are:
T then U: aBranch.create(“Z”); z.deposit(10);z.deposit(20). Z’s final balance is $30.
U then T: z.deposit(10); z.deposit(20); aBranch.create(“Z”). Z’s final balance is $0. Therefore the example is not a serially equivalent execution of T and U.