Re: Bitmap Join Indexes
- From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 13 Feb 2004 09:44:28 -0000
In principle, there should be no reason why
these two features should not be used together.
Query rewrite operates by examining MVs,
base tables, constraints, and dimensions to
produce SQL that can satisfy the original
query. It then passes this SQL and the original
SQL through the optimizer to calculate the cost
and see which one is cheaper.
The first step OUGHT to be independent
of bitmap join indexes, the second step
OUGHT to consider bitmap join indexes
in the standard way. So there seems to be
reason why the two features should collide.
However, it is often the case that features
are disabled (in initial releases) for no apparent
reason.
One of my articles on www.dbazine.com talks
about the bitmap join index - this may give you
some ideas about potential costs and benefits.
Bottom line, really, is that they can take MUCH
longer than simple bitmap indexes to build, and
you almost certainly have to drop or mark them
as unusable when you load new data.
Regards
Jonathan Lewis
http://www.jlcomp.demon.co.uk
The educated person is not the person
who can answer the questions, but the
person who can question the answers -- T. Schick Jr
Next public appearances:
March 2004 Hotsos Symposium - The Burden of Proof
March 2004 Charlotte NC OUG - CBO Tutorial
April 2004 Iceland
One-day tutorials:
http://www.jlcomp.demon.co.uk/tutorial.html
Three-day seminar:
see http://www.jlcomp.demon.co.uk/seminar.html
____UK___February
____UK___June
The Co-operative Oracle Users' FAQ
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----- Original Message -----
From: "Freeman, Donald" <dofreeman@xxxxxxxxxxx>
To: "Oracle-L (E-mail)" <oracle-l@xxxxxxxxxxxxx>
Sent: Thursday, February 12, 2004 9:17 PM
Subject: Bitmap Join Indexes
In our datawarehouse we chose to go with materialized views and query =
rewrite to speed up our report performance. Ever since I read about =
Bitmap Join Indexes I've been wondering whether these are exclusive =
features, or can be implemented together, or one or the other is =
superior. I'm not sure how to evaluate the benefit of these features. =
Would someone comment?
Don Freeman
Database Administrator
Bureau of Information Technology
PA Department of Health
717-783-4743 Ext 337
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