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| Updating SAS OLAP Cubes |
Coalescing Cube Aggregations
The Incremental Update function enables you to add new members to a cube and update data. Every time a cube update is done, the incremental aggregation data is written to a new SPDE table (rack). The more cube updates that have been completed, the more tables or racks there are that must be read during a query, and the slower the access time can be.
Periodically, it can be beneficial for performance reasons to combine all of the individual tables into a single aggregation table. Aggregations are coalesced (combined) in a separate job from adding data to a cube. Only aggregations with more than one rack are coalesced. The COALESCE_AGGREGATIONS option can be executed only for the most current generation of the cube. In addition, only MOLAP aggregations (those aggregations created by PROC OLAP) can be coalesced. The coalesce task is processed in-place. A new generation of the cube is not created.
After the cube generation is coalesced, it is no longer dependent on the aggregation data from previous generations. If those generations have already been deleted, then the old aggregation tables are also deleted.
You can coalesce all the aggregations by using the COALESCE_AGGREGATIONSoption on the PROC OLAP statement. In addition, the Coalesce wizard is available in SAS OLAP Cube Studio.
See Coalesce Incremental Data for a Cube for a discussion of coalescing cube aggregations with the SAS OLAP Cube Studio Incremental Update wizard.
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