Indexing option on numeric fact referred to in DW Toolkit 2nd edition

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Indexing option on numeric fact referred to in DW Toolkit 2nd edition

Post  dennisf on Tue Apr 14, 2009 4:58 pm

In the 2nd edition of THE DATA WAREHOUSE TOOLKIT, Chapter 9, page 208 at the end of the first paragraph, there is a reference to an indexing option on a numeric fact pioneered by SYBASE IQ product which has become a standard indexing option in competing databases. I would like to know what is the equivalent indexing option in Oracle?

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Re: Indexing option on numeric fact referred to in DW Toolkit 2nd edition

Post  ngalemmo on Mon May 18, 2009 3:08 pm

I believe it is referring to bitmap indexes.

Sybase IQ is a 'column oriented' data base. It implements tables as a series of bitmap vectors for each unique value in each column in the table. The vectors are compressed, so overall, the database is smaller than the raw data it holds (if stored in a traditional row).

In Oracle, implementing bitmap indexes allow you to take advantage of the star query optimiser. Fact tables should be defined with bitmap indexes on each foreign key column (local indexes if the table is partitioned), one index per column. If all goes well, Oracle should resolve predicates against the dimensions, then using the list of subject dimension foreign keys, apply them en-masse against the bit vectors to isolate the rows in the fact table. It provides fast, consistant query times regardless of the query.
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