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AnsPrac8db05 - Page 1 CP3020 Answer to Practice Week 8...

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Page 1 24/12/2009 CP3020 Answer to Practice Week 8 17.14 Change transaction T 2 in Figure 17.2 (b) to read: read item(X); X := X+M; if X > 90 then exit else write_item(X); Discuss the final result of the different schedules in Figure 17.3 where M = 2 and N = 2, with respect to the following questions. Does adding the above condition change the final outcome? Does the outcome obey the implied consistency rule (that the capacity of X is 90)?   FIGURE 17.2 FIGURE 17.3 File: //home/vdimitrov/6057/e90e44193ecf7f83183a1e6df6a262583ab5d07c.doc School of Information Technology, James Cook University
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Page 2 24/12/2009 FIGURE 17.3 (continued) Answer: The above condition does not change the final outcome unless the initial value of X > 88. The outcome, however, does obey the implied consistency rule that X < 90, since the value of X is not updated if it becomes greater than 90. 17.17 List all possible schedules for transactions T 1 and T 2 from figure 17.2, and determine which are conflict serializable (correct) and which are not.
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