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Introspecting Large Datasets with SAP BW
Large data sources with complex schemas, big tables, lots of columns, or many dimensions have a correspondingly large amount of metadata that can pose special challenges for TDV. For TDV, it is not the amount of data stored, but rather the complexity and amount of metadata that defines the data source that is the most important factor for performance, particularly during introspection.
To work with large datasets and prevent runaway MDX queries when using SAP BW within TDV
1. When defining your SAP BW data source, on the Advanced tab, set the Allow large (>1M cells) datasets check box. For other data source definition information, see About SAP BW Data Sources.
This specifies that large datasets that are greater than 1M cells can be introspected. By default, datasets that are larger than one million cells cannot be introspected.
2. Define an OLAP View, following the instructions in Creating a View from a Cube.
3. For your OLAP View, generate the Execution Plan. See Generating an OLAP View Execution Plan.
4. Review the Estimated Rows Returned value that is displayed for the Execution Plan.
5. Review the other information displayed in the execution plan. If TDV estimates that your query could return more than one million cells of data from the SAP BW database, the FETCH node of the Cardinality Statistics panel displays a message indicating this and suggesting that you define some constraints on the query to limit the data set to return.
6. Determine if limiting the number of dimensions used for the OLAP View could improve retrieval of the dataset. See Creating an OLAP View.
7. Determine if adding filter conditions would help improve performance. See Creating Filter Conditions on an OLAP View.
8. Save your work and run another Execution Plan for comparison.
9. Set up and use a test system to determine if the performance of the OLAP View is acceptable.