Consider the use of timestamp ordering with each of the example inter leavings of transactions T… 1 answer below »

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Consider the use of timestamp ordering with each of the example inter leavings of transactions T and U in Exercise 16.9. Initial values of ai and aj are 10 and 20, respectively, and initial read and write timestamps are t0. Assume that each transaction opens and obtains a timestamp just before its first operation; for example, in (a) T and U get timestamps t1 and t2, respectively, where t0 1 2. Describe in order of increasing time the effects of each operation of T and U. For each operation, state the following:

i) Whether the operation may proceed according to the write or read rule;

ii) When timestamps are assigned to transactions or objects;

iii) When tentative objects are created and when their values are set.

What are the final values of the objects and their timestamps?

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.