url - Universität zu Lübeck

116 CHAPTER 6. THE INDEX SELECTION PROBLEM
dates and small workloads this can still be done in acceptable time.
n k d p 1 p 2 p 1 /d p 2 /d
I 1 1,088 1,337 60.2 248.3 233.4 4.125 3.877
I 2 11,057 50,035 975.8 481.8 456.4 0.494 0.468
I 3 1,004 1,004 53.2 1,016.1 1,001.2 19.100 18.820
I 4 122,305 305,806 8,317.2 411.3 390.6 0.049 0.047
I 5 41 1,337 15.1 548.6 454.1 36.331 30.073
I 6 147,668 151,268 7,862.4 567.9 552.2 0.072 0.070
I 7 51 30,806 3,060.3 1,136.3 824.5 0.371 0.269
I 8 150,264 150,264 7,964.0 1,546.4 1,530.6 0.194 0.192
Σ 28,307.6
Table 6.1: Characteristics of the index candidates (n: number of keys, k : number
of return values, d: space consumption in kilobytes, p i : profit of workload W i )
A comparison between the gained profits of the exact solution and both heuristics
H rank and H div is presented in table 6.2.
Exact
selected Indices p Σ d Σ
W 1 I 1 , I 2 , I 3 , I 5 , I 8 3,841.2 9,068.3
W 2 I 1 , I 2 , I 3 , I 5 , I 8 3,675.7 9,068.3
H rank
selected Indices p Σ d Σ
W 1 I 8 , I 3 , I 5 , I 2 , I 1 3,841.2 9,068.3
W 2 I 8 , I 3 , I 2 , I 5 , I 1 3,675.7 9,068.3
H div
selected Indices p Σ d Σ
W 1 I 5 , I 3 , I 1 , I 2 , I 7 3,431.1 4,164.6
W 2 I 5 , I 3 , I 1 , I 2 , I 7 2,969.6 4,164.6
Table 6.2: Comparison of exact solution and heuristics H rank and H div (p Σ : total
profit, d Σ : total space consumption)