BW Accelerator

BW Accelerator - General Information

Purpose

BW accelerator (BWA) allows you to improve the performance of BI queries when data is read from an InfoCube. The data of a BW InfoCube is made available as a BW accelerator index in a compressed but not aggregated form.
BW accelerator is particularly useful in cases where relational aggregates or other BI-specific methods of improving performance (such as database indexes) are not sufficient, are too complex, or have other disadvantages.
For example, if you have to maintain a large number of aggregates for one particular InfoCube, you can use the BW accelerator to avoid this high maintenance effort. Unlike performance optimization with aggregates, there is only one BW accelerator index for each InfoCube. Like performance optimization with aggregates, you do not have to make any decisions with regard to modeling for the BI accelerator index.

Implementation Considerations

The BW accelerator is based on TREX technology. To use the BW accelerator, you need an installation based on 64-bit architecture. Hardware partners deliver this variant in preconfigured form as the BI accelerator box. Note that you cannot use a TREX installation configured for searching in metadata and documents with the BI accelerator since TREX installation is based on a 32-bit architecture. Equally, a BI accelerator box cannot be used for searching in metadata and documents. If you want to use the search function as well as the BI accelerator, you require two separate installations.
For more information, see the following SAP Notes:
[Note 883726] TREX 7.0: Central Note SAP NetWeaver BW accelerator
[Note 902533] TREX 7.0: HowToGuide Connecting/Operating BW Accelerator Box

Integration

Accessing the OLAP Processor

You can use relational aggregates and a BW accelerator index for the same InfoCube. A BW query always tries to use performance-optimized sources by checking the sources from which it can draw the requested data. It checks the sources in the following order:

1. OLAP cache.
2. BW accelerator index.
3. Relational aggregates from the database.
4. InfoCubes from the database.

If an active BW accelerator index exists, the OLAP processor always accesses this BW accelerator index and not the relational aggregates. Therefore, with regard to modeling, we recommend that you create either relational aggregates or a BI accelerator index for an InfoCube.

Query Execution

When the query is executed, it is clear to the user whether data is being read from an aggregate, a BW accelerator index, or an InfoCube.
In the maintenance transaction, you can deactivate a BW accelerator index on a temporary basis to test it for performance purposes or to analyze data consistency.
You can also execute the relevant query in the query monitor (transaction RSRT) using a corresponding debug option: Choose   Execute + Debug. In the Debug Options dialog box, choose Do Not Use BI Accelerator Index to execute the query with aggregates or an InfoCube.
 

BW Accelerator Architecture Diagram