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/Os 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
|
|