Make a comparison of the sequences of operations of the transactions T and U of Exercise 16.8…

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Make a comparison of the sequences of operations of the transactions T and U of Exercise 16.8 that are possible under two-phase locking (Exercise 16.9) and under optimistic concurrency control (Exercise 16.16).

Exercise 16.16

Consider optimistic concurrency control as applied to the transactions T and U defined in Exercise 16.9. Suppose that transactions T and U are active at the same time as one another. Describe the outcome in each of the following cases:

In each case describe the sequence in which the operations of T and U are performed, remembering that writes are not carried out until after validation.

Exercise 16.9

The transactions T and U at the server in Exercise 16.8 are defined as follows:

Initial values of ai and aj are 10 and 20, respectively. Which of the following inter leavings are serially equivalent, and which could occur with two-phase locking?

Exercise 16.8

Explain why serial equivalence requires that once a transaction has released a lock on an object, it is not allowed to obtain any more locks.

The transactions T and U are defined as follows:

Describe an interleaving of the transactions T and U in which locks are released early with the effect that the interleaving is not serially equivalent.