Comments on: Cost Based Optimizing through time travel? – the value of meta-data for enabling Query Rewrite

By: Maxim

Maxim — Fri, 21 Apr 2006 14:20:10 +0000

That are indeed exciting features, interesting is as well, the rewrite can be “bidirectional”, i.e. if your materialized view is built on count(*) and avg(*), it is used to query a sum (it means formula to calculate the total sum from partial averages and partial counts is known to Query Transformer), there are even much more complex transformations known ( total variance can be calculated from partial variances etc). Also big help to recognize rewrite capabilities does dbms_mview.explain_rewrite.

Regards

Maxim

By: Karl

Karl — Fri, 21 Apr 2006 10:10:24 +0000

Yes!
i got it!
http://download-uk.oracle.com/docs/cd/B19306_01/server.102/b14211/optimops.htm#i82005

The Query Optimizer (CBO)
has following sub components
- Query Transformer (what i meant with Query Rewriter )
- Estimator
- Plan generator
Thanks greetings

Interesting is that the Documentation of 10G does not talk about CBO at the given link but of the ‘Query Optimizer’
Greetings
Karl

By: Alex Nuijten

Alex Nuijten — Fri, 21 Apr 2006 08:50:29 +0000

Karl, according to the documentation it’s the CBO that’s responsible for the query rewrite.
http://download-west.oracle.com/docs/cd/B10501_01/server.920/a96520/qr.htm#29014

Great article btw…

By: Karl

Karl — Fri, 21 Apr 2006 08:21:38 +0000

Great article!
‘That means that we allow the Cost Based Optimizer to make use of this MV’
I am not sure about this : Not CBO rewrites the Query but a Component call Query Rewriter? the Query Rewriter rewrites the Query and then let’s the CBO evalualte the costs? Then out of the set of rewritten queries the lowes cost rewritten query is used.
Greetings
Karl

By: Marco Gralike

Marco Gralike — Thu, 20 Apr 2006 22:54:20 +0000

Great example. Thanx