url - Universität zu Lübeck
url - Universität zu Lübeck
url - Universität zu Lübeck
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118 CHAPTER 6. THE INDEX SELECTION PROBLEM<br />
For the first two measurements we set up artificial workloads based on XMark<br />
data [104]. XMark produces scalable and highly structured data so that a multitude<br />
of different and reasonable queries are expressible. The test document has<br />
a size of 11 MB.<br />
Test Scenario 1<br />
For the first set we created two different classes of querying database operations:<br />
The first class A contained person-based queries while the second class B consisted<br />
of queries that operate on the items to be sold at the auction. Afterwards,<br />
we constructed several workloads with different distributions of the operations<br />
from A and B. The first workload only had operations from class A while the<br />
ongoing workloads have a growing percentage of operations from B. The last<br />
workload consists analogously of operations from B only. This scenario simulates<br />
a change in the typical usage of the database. All workloads have 100 operations<br />
in total.<br />
In figure 6.4 we present the time measurements for execution of the workloads<br />
without an index and an index that is optimized for the first workload (only operations<br />
from A). The figure shows that the index suits well for the first time but<br />
becomes more and more useless because it cannot accelerate the operations from<br />
class B.<br />
Figure 6.4: Test 1: Measurements without an index and with one initial set of<br />
indexes.
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