star_transformation_enabled

Why would enabling STAR_TRANSFORMATION_ENABLED for a non-star query produce a significantly faster query? I have a query that went from about 10 seconds to < 1 second after enabling it. The documentation's description for the parameter is...

"This parameter, if set to true, enables the CBO to cost a star transformation for star queries. The star transformation combines the bitmap indexes on the various fact table columns rather than using a Cartesian approach."

None of the tables in my query have bitmap indexes. The table you would normally consider to be a "fact" table in my query is not a table at all but rather a dynamic view of an aggregate on a join of two medium sized tables (about 100k rows each). If run separately the view returns about 100k rows.

Is there a downside to enabling this parameter on a database that is mainly OLTP? Received on Tue Feb 04 2003 - 15:12:34 CST