Quality

           The most important aspect of an optimizer is the quality of the plans it generates.

           The quality of a plan can be measured in terms of the difference between the actual cost of executing the plan produced by the optimizer and the actual cost of executing the best possible plan that could be run on the DBMS's Query Execution Engine. Table 7.7 shows the estimated cost in minutes of elapsed time for the plans produced by the Model D optimizer for each of the 17 TPC-D queries.

Table 7.7: Cost of Plans Produced by Optimizing TPC-D Queries 


Query	#joins	   Estimated Run Time* (minutes)

1         0                22.4
2         4                 5.1
3         2                32.8
4         1                26.8
5         5                26.5
6         0                19.6
7         5                29.5
8	  7		   27.4
8y        6                16.4
9         5                26.3
10        3                40.5
11        2                 4.7
12        1                23.8
13        1                25.7
14        1                19.0
15        1                17.8
16        2                 5.1
17        3                21.8

*  Using left deep joins.


           Because we were not able to run an actual DBMS to calibrate the cost model, the estimated costs shown in the tables below and the cost savings (or lack of cost savings) resulting from use of particular transformation or implementation rules must be considered suspect.

7. Results:    <Extensibility> <Efficiency> <Heuristics> <Accuracy> <Quality> <Agg Push Down> <Indices>
  7.1: Rules     7.2: Efficiency     7.3: Statistics     7.4: Heuristics     7.5: Search Space     7.6: Cardinalities     7.7: Costs     7.8: Agg     7.9: Indices  

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