Aggregation is an internal feature in the Visual Business Director (VBD) data set to reduce the number of records that the VBD data set needs to store on its partitions. The size of a partition is determined by the time granularity setting that you select when you create a VBD data set instance. When you save the rule instance, you cannot change this setting.
Aggregation happens automatically for each VBD data set when a new partition is allocated in the VBD data set instance and at midnight. Records in older partitions that have not been aggregated, are aggregated.
Example of how aggregation works
A data flow inserts five records into an empty VBD data set. Three records are identical.
When the records are inserted, they have not been aggregated yet. The number of records is displayed in the # Records column. After the aggregation is started automatically or you click Aggregate in the Data Sources tab, identical records are reduced to one record but their number is tracked.
As a result, five records in the VBD data set were reduced to three by adding an internal Count field to them, and using it to tally records with identical field values. The same happens with subsequent aggregations.