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Home -> Community -> Mailing Lists -> Oracle-L -> RE: Bitmap Join Indexes
Your treatment of the subject in the articles you authored seems the =
best I have seen so far on the subject. It's going to take some time to =
see if this feature is going to be useful in our environment. The space =
and time required to (re)build them isn't an issue. We have a lot of =
room in our load schedule. We just have to find some candidate =
tables/reports that would benefit.
Thanks,
Don Freeman
-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Jonathan Lewis
Sent: Friday, February 13, 2004 4:44 AM
To: oracle-l_at_freelists.org
Subject: Re: Bitmap Join Indexes
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=20
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=20 who can answer the questions, but the=20 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
http://www.jlcomp.demon.co.uk/faq/ind_faq.html
In our datawarehouse we chose to go with materialized views and query =
=3D
rewrite to speed up our report performance. Ever since I read about =3D
Bitmap Join Indexes I've been wondering whether these are exclusive =3D
features, or can be implemented together, or one or the other is =3D
superior. I'm not sure how to evaluate the benefit of these features. =
=3D
Would someone comment?
Don Freeman
Database Administrator
Bureau of Information Technology
PA Department of Health
717-783-4743 Ext 337
FAQ is at http://www.freelists.org/help/fom-serve/cache/1.htmlput 'unsubscribe' in the subject line.
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