RE: Hybrid histograms in 11g ?
- From: "Bobak, Mark" <Mark.Bobak@xxxxxxxxxxxxxxx>
- To: <makulev@xxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 20 Jul 2007 10:51:49 -0400
I believe this is the ability of 11g to create histograms on multiple columns.
This helps Oracle deal with columns that are correlated. If you have a column
"BIRTH_MONTH" and a column "ZODIAC_SIGN", you can say that 1/12 of the
population will have a BIRTH_MONTH of DECEMBER, and 1/12 of the population will
have a ZODIAC_SIGN of TAURUS. If you ask the optimizer to estimate how many
people have a BIRTH_MONTH of DECEMBER and a ZODIAC_SIGN of TAURUS, it will
estimate 1/144. But, we know the answer is 0 (since TAURUS is only people born
between Apr. 20th - May 20th). With histograms on multiple columns, the
optimizer will now be able to understand these types of correlations and handle
them correctly. This will allow for much better cardinality estimates.
Hope that helps,
-Mark
PS I'm not an 11g Beta tester. The above is based purely on what I've read
and heard about 11g, and could be completely wrong.
--
Mark J. Bobak
Senior Database Administrator, System & Product Technologies
ProQuest
789 E. Eisenhower, Parkway, P.O. Box 1346
Ann Arbor MI 48106-1346
734.997.4059 or 800.521.0600 x 4059
mark.bobak@xxxxxxxxxxxxxxx
www.proquest.com
www.csa.com
ProQuest...Start here.
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On
Behalf Of Milen Kulev
Sent: Friday, July 20, 2007 5:19 AM
To: oracle-l@xxxxxxxxxxxxx
Subject: Hybrid histograms in 11g ?
Hi listers,
I have just read the Oracle White paper:
http://www.oracle.com/technology/products/database/oracle11g/pdf/performance-11g-whitepaper.pdf
On page 11 there is a following statement:
"
...
ding better information to the CBO by correlating statistics, such as Number of
Distinct Values (NDV) and histograms, on multiple column
...
"
Are these so called "Hybrid histograms" ?
If yes, is there still a constraint of 254 buckets per histogram?
Any ideas, experiences from "early birds" in this list ?
Best Regrads.
Milen
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