If you provide values for the map and join column properties, the Actuate SQL compiler uses these values to do cost-based query optimization. You can disable cost-based optimization using the pragma EnableCBO.
If you provide values for the map and join column properties, part of the query plan looks similar to Figure 7-1.
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Figure 7-1
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Example of part of the query plan for which values for the map and join column properties have been provided
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Figure 7-2
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Disabling cost-based optimization changes the join sequence and the join algorithm. The Customer and LineItem, Supply database subqueries switch positions, and the merge join is replaced with a nested loop join.
If you create a query using an information object for which cost-based optimization is disabled, cost-based optimization is disabled for the query as well.
You can disable cost-based optimization for all information object queries by setting the BIRT iServer configuration variable Enable cost based optimization to False. For more information about BIRT iServer configuration variables, see Configuring BIRT iServer.
