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Home -> Community -> Mailing Lists -> Oracle-L -> 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
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
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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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