9.6 Exercises

  1. Consider the flow of control given in the Clisspe specification of Fig. 9.10 where a, b, ...,e are statements. Give an expression for the service demand Di at device i as a function of the service demands graphics/245fig01.gif through graphics/245fig02.gif.

    Figure 9.10. Pseudo code for Exercise 9.1.


  2. A bank is considering the development of a new application to support a phone banking system. Customers will be allowed to dial into the bank and choose, from a touch-tone phone, one of two transactions: access balances and transfer funds. If a customer chooses to access balances, they can select from their checking or savings accounts. If a customer selects to transfer funds, they are asked to specify the type of account (checking or savings) from which to transfer funds and the type of account into which the funds are to be transferred. Customers are then requested to enter the amount to be transferred. A transfer confirmation number is returned to the customer. Estimate the service demands for this new application and plot the response time as a function of the arrival rate. For which value of the arrival rate will the response time exceed 1 sec? Make the following assumptions:

    • The computer system that will support the application consists of a CPU and two identical disks. The average service time on these disks is 8 msec.

    • Every customer has an identification number (ID) and a pin number that must be entered before any transaction can take place.

    • The following files will be managed by the application: CUSTOMERS (contains one record per customer, keyed by the customer ID), CHK_ACCOUNTS (for checking accounts, keyed by the customer ID), SAV_ACCOUNTS (for saving accounts, keyed by customer ID), HISTORY (contains an audit trail of all transactions executed, keyed by transaction date).

    • Two physical I/O operations are needed on average to retrieve a record given a customer ID from the CUSTOMER, CHK_ACCOUNTS, or SAV_ACCOUNTS files.

    • A total of 60% of the calls are expected to request only balance information on one account, 30% are expected to first request balance information on one account and then request a funds transfer involving this account and another account, and 10% are expected to request funds transfer without requesting balance information first.

    • The CPU time per I/O is equal to 0.5 msec.

    Make and justify any additional assumptions, including the file distributions on the two disks.

  3. A university wants to develop a new application to allow students to register by phone at the beginning of each semester. Students dial a special number and are requested to enter their student identification number and the codes of the specific courses for which they wish to register. Conduct an application sizing to compare the following two alternatives:

    • Minimal consistency check. In this alternative, the only consistency checks that are performed on-line involve verifying if the selected courses are indeed being offered. The student's registration request is recorded into a file in the order of arrival to be processed later in batch mode. No registration confirmation is issued by the on-line transaction.

    • Complete registration processing. In this case, besides checking availability of the courses requested, the transaction should check whether the student has completed all prerequisites and whether the selected classes are still open. If any class is not open, the student should be placed on a waiting list. A registration confirmation number is given back to the student by the system.

    Use the same assumptions about the hardware platform of Exercise 9.2. Make and justify any other assumptions necessary to determine the service demands of the new on-line registration application. Assume that the university has 25,000 students, that the system will be on-line for phone registration 24 hours a day for two weeks, and that each student requests enrollment in five courses on average. Determine the average response time for each of the two cases (i.e., minimal consistency check and complete registration processing).

  4. Use the Ch09-Data.XLS MS Excel workbook to recompute the number of I/Os generated by the status viewing transaction if an index on EmployeeId is not available for the TicketEmployee table.

Performance by Design. Computer Capacity Planning by Example
Performance by Design: Computer Capacity Planning By Example
ISBN: 0130906735
EAN: 2147483647
Year: 2003
Pages: 166

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