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).
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.
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?
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.