With a write-back partition, you can update data on-the-fly in the target block storage database while the data in the source aggregate storage database remains unchanged. Creating a write-back partition potentially decreases calculation time and reduces database size.
When creating write-back partitions, follow these guidelines:
Create the block storage database in a separate application from the one in which the aggregate storage database is located.
Typically, the block storage database contains a subset of the dimensions in the aggregate storage database.
Create a transparent partition based on where you want the data to be stored. Make the block storage database the target and the aggregate storage database the source.
See Designing Partitioned Applications.
You may want to partition on the time dimension if data for some time periods is stored in the aggregate storage database and data for other time periods is stored in the block storage database. For example, if you have actual data for January through March, which is stored in an aggregate storage database, and you want to budget for the last nine months of the year using write-back members in a block storage database. |
Users query and write-back to the block storage database. Queries are processed by the block storage database or transparently by the aggregate storage database.
You need Database Manager permissions to create a partitioned application.
Figure 158, Transparent Partition Used for Analyzing Variance Between Forecast and Actual Data illustrates using a transparent partition for analyzing the variance between forecast and actual data:
The following procedure is based on the aggregate storage sample database (ASOsamp.Sample), and uses the Administration Services Aggregate Storage Partition Wizard (see the Oracle Essbase Administration Services Online Help).
To create a write-back partition:
Select the ASOsamp.Sample database, which contains the actual data for the current year and for previous years.
See Figure 159, ASOsamp.Sample Aggregate Storage Database Outline.
Create a block storage database containing the following subset of dimensions from ASOsamp.Sample: Measures, Years, Time, Products, Stores, and Geography.
Edit the Years dimension to add the following members to the block storage database outline:
Delete the following member formulas:
These formulas are expressions written in MDX that are copied from the aggregate storage database. MDX formula expressions cannot be interpreted in block storage databases.
Link the databases with a transparent partition on the Years dimension, with the block storage database (forecast data) as the target and the aggregate storage database (actual data) as the source.
Do not include the write-back members (Forecast and Variance) in the partitioned area.
When using the Administration Services Aggregate Storage Partition wizard, this step is automatic. The databases are automatically partitioned on the Years dimension because you selected the Years dimension in step 3. The write-back members are not included in the partitioned area. |
You input forecast values into the block storage database write-back members. Because the added members are outside the partitioned area, you can write to them and then calculate data and generate reports based on updated data. The transparent partition provides a seamless view of both databases.