Tuning of BWA – FEMS compression |
Within this blog (maybe there will be more posts) I want to focus on performance issues with SAP Business Warehouse Accelerator (BWA).
Some experienced BWA admin may just laugh seeing this post. However there are some customers out there not knowing about this feature of BWA. The fact is that FEMS compression is BWA feature aimed for reduction of transport costs. This is meant in terms of an intelligent compression schema. Moreover elimination of duplicates in query results directly on the BWA side is enabled. Setting this feature ON can improve performance of BWA.
FEMS are Formula EleMent Selections (or also Finite EleMent Solver) carrying information about structure elements where certain value belongs. Database and BWA are giving records by exploding structure elements. These records are than assigned to correct structure elements by the OLAP. FEMS compression enables merge of duplicate structure elements in BWA part and makes OLAP par being able to process this information. All together there is a reduction of information traffic between BWA and BW backend.
In which BWA version is this feature available?
In every BWA starting version 70 with revision 48 and higher.
Where to check status of this setting in your BWA?
Start TREX Admin Tool (e.g. on your operation system shell: <TREX_DIR> = /usr/sap/<SAPSID>/TRX<instance_number>). Open screen area Landscape -> Ini. See current settings in configuration file TREXIndexServer.ini in its [OLAP] section.
Where to set this setting?
See above configuration file TREXIndexServer.ini. Add parameter in to file: fems_compression = on.
In general settings FEMS compression ON is always advisable. Setting this ON has no influence on BWA’s indices size. You may only be asked by SAP to switch it off in situation that you raised BWA problem message (e.g. wrong data provided by BWA based query vs. proper data given by same query running without BWA) to SAP via SMP channel. If issue cannot be quickly analyzed SAP may ask you to switch compression off to help them isolate issue.
Information sources used for this blog:
SDN forum Thread: FEMS Compression
SAP documentation: Enabling 'FEMS Compression'
SDN blog: BIA BLOG Series, Part VIII: Improvements and major parameter changes for BI Accelerator
SAP Note 1074953 - FEMS, BIA optimization
Note 1118425 - BIA 7.00: Activate performance feature FEMS compression
Martin Maruskin SAP NetWeaver BW certified consultant
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