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Consider The Validation-based Concurrency-control. Show That By Choosing Validation(ti), Rather Than Start(ti), As The Time Stamp Of Transaction Ti, We Can Expect Better Response Time Provided That Conflict Rates Among Transactions Are Indeed Low? |
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Answer» In the concurrency control SCHEME choosing Start(Ti) as the time stamp of Ti gives a subset of the schedules ALLOWED by choosing Validation(Ti) as the time stamp. USING Start(Ti) means that whoever started FIRST must finish first. Clearly transactions could enter the validation phase in the same order in which they began executing, but this is overly restrictive. Since choosing Validation(Ti) causes fewer non conflicting transactions to restart, it gives the better response TIMES. In the concurrency control scheme choosing Start(Ti) as the time stamp of Ti gives a subset of the schedules allowed by choosing Validation(Ti) as the time stamp. Using Start(Ti) means that whoever started first must finish first. Clearly transactions could enter the validation phase in the same order in which they began executing, but this is overly restrictive. Since choosing Validation(Ti) causes fewer non conflicting transactions to restart, it gives the better response times. |
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