Previous Table of Contents Next


TABLE 14.4 Measured Performance of a Database Information System

Number of
Days
Elapsed
Time

1 0.65
2 0.79
4 1.36
8 2.26
16 3.59
25 5.39

14.5  In the second phase of Exercise 14.4, the analyst measured the elapsed time as a function of the complexity of the query. The complexity was measured by the number of keywords in the query. The number of disk-read operations were also measured, as shown in Table 14.5. For this data prepare regression models to predict the elapsed time as a function of number of keywords and interpret the results.
TABLE 14.5. Database Performance as a Function of Number of Keywords

Number
of Keywords
Elapsed
Time
Number of
Disk Reads

1 0.75 3
2 0.70 6
4 0.80 7
8 1.28 78
16 1.60 92

14.6  Prepare a regression model to predict the number of disk I/O’s as a function of the number of keywords for the data presented in Table 14.5.
14.7  The time to encrypt a k-byte record using an encryption technique is shown in Table 14.6. Fit a linear regression model to this data. Use visual tests to verify the regression assumptions.
TABLE 14.6 Measured Encryption Times for Various Record Sizes

Observations
Record
Size 1 2 3

128 386 375 393
256 850 805 824
384 1,544 1,644 1,553
512 3,035 3,123 3,235
640 6,650 6,839 6,768
768 13,887 14,567 13,456
896 28,059 27,439 27,659
1,024 50,916 52,129 51,360


Previous Table of Contents Next

Copyright © John Wiley & Sons, Inc.