Improving Efficiency Using BI Accelerator Delta Indexes
You can create a delta index for a BI accelerator index. If a delta index exists, the system does not write to the main index during each delta indexing or each indexing activity (except the initial filling/indexing) and the main index is not optimized. Instead, the system writes data to a second index which has the same structure as the main index but is usually smaller. The smaller the delta index, the faster the subsequent optimize procedure and therefore, the whole process of rolling up data or making modifications after a hierarchy or attribute change run.
As read performance deteriorates the larger the delta index gets, we recommend that you only switch on the delta index for essential indexes such as fact indexes and X/Y indexes. This improves performance when you modify data after a hierarchy or attribute change run.
We recommend that you regularly merge the delta indexes with your main index so that read performance is not negatively affected. You can do this in several ways:
- On the Analysis and Repair of BI Objects screen (transaction RSRV), area BI Accelerator -> BI Accelerator Performance, you can select the Size of Delta Index elementary test. You can choose Correct Error to access repair mode and then execute a MERGE for the indexes.
- You can schedule program RSDDTREX_DELTAINDEX_MERGE.
To set the delta index for a BI accelerator index, on the BI Accelerator Monitor screen, choose BI Accelerator -> Index Information -> Set Delta Index. The Delta Index Properties dialog box appears.
Switching On the Delta Index
In the Delta Index column, set the corresponding indicator if you want the table to use a delta index.
The new setting takes effect with the next delta indexing operation.
Switching Off the Delta Index
You reset the setting for the delta index in the same way.
Before the next indexing operation, the system merges the delta index and the main index. If the delta index is already very large, the next process may take longer.