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Using ProcessingGroup Dimension property option ByTable vs. ByAttribute may error with string keys

In SSAS 2005 and later, there is a dimension property called ProcessingGroup.  It has two values; ByAttribute (default) and ByTable. 

When you use ByAttribute, SSAS will send a SELECT DISTINCT query to the relational engine for each attribute PLUS, at the end, an additional SELECT DISTINCT that combines all the attributes plus key.  As you can imagine, if you have several attributes and a very large dimension table, this process can take a while.  Our customer in this case has a 100 million members dimension table in Oracle.

Using the option ByTable, SSAS sends one table scan query to the relational engine and temporarily caches in memory the results.  This can work well only if you have enough memory for the cache (see related blog for potential issues here). 


Tags: management, process


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