Re: Cost of Access Plan using Bitmap Indexes

Just in case you haven't seen then, there are three articles that I wrote about bitmap indexes on www.dbazine.com - they might
give you some extra ideas.

Using a larger value for bitmap_merge_size MIGHT make the actual run-time a bit shorter, but I don't think it changes the cost that Oracle uses in its calculations - but I'd have to test that carefully to be sure.

--
Regards

Jonathan Lewis
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"Fabrizio Napolitano" <fnapolitano_at_belgacom.net> wrote in message
news:7a96ec4520e69b2f93ab7ea608ebfe82.119705_at_mygate.mailgate.org...


> Jonathan thanks a lot.

>

> Your advices are great food for thought and help me understand

> the picture behind.

>

> Still one question remain:

> in the Oracle Datawarehousing guide there is a lot

> of enphasis on Bitmap indexes and the way they can

> be merged easily by the optimizer helping getting

> the best from the very different report (SQL) that can

> be generated in a DSS environment,but at the moment I

> have seen that CBO consider even a full table scan

> way cheaper then the bitmap indexes.

>

> Considering that fact tables are pretty big

> is my only option  to be killed by millions of phisycal reads

> or to go for hints?

> that by the way not always can be implemented?

>

> thank you very much again and hope to see other good advices on the

> topic.

>

> P.s. using a bigger Bitmap_sorting _area could help cutting the

cost?


>

> Best Regards,

> Fabrizio

>

>

>

> --

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