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?
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.