||CS245A PROBLEM SET #7|
Due by 5pm, Thursday, March 12, 1998.
4 problems, equal credit. 100 pts.
Problem 1: Group Modes in Lock Tables
Consider the shared/exclusive/warning scheme described in class
and in the lecture notes. In the table below you are given six
different cases of simultaneously held locks on some object. In each
case, give the group mode that is stored in the lock
table, or explain briefly why the situation is
|i||S, S, IS|
|ii||SIX, S, SIX|
|iii||IX, IS, IS|
Problem 2: Tree locking
Suppose we have three transactions, T, U, and V that obey the
tree protocol described in class and in the notes. Transaction
T locks A, B, C, and E; U locks C and F; V locks B and E. In
how many ways can T, U, and V be scheduled legally if A, B, C,
D, E, and F are organized in the following hierarchy.
Problem 3: Timestamps vs. 2PL
Show that neither two-phase locking nor timestamp-based
concurrency control is more general than the other by giving an
example of a schedule that is 2PL but not timestamp compliant
and an example of a schedule that is timestamp compliant but not
2PL. Make your two examples as simple as possible.
Problem 4: View-Serializability
Consider the following schedule of three transaction, T, U, and V:
Show the polygraph for this schedule. Is this schedule
view-serializable? Briefly explain your answer.