Re: Tuning By cardinality Estimates

From: (wrong string) 조동욱 <ukja.dion_at_gmail.com>
Date: Sat, 7 Mar 2009 14:08:35 +0900
Message-ID: <43c2e3d60903062108m523300bdhe605a023eb0212eb_at_mail.gmail.com>

But how does extended statistics solve the problem of join skewness by correlation?

I believe that extended statistics in Oracle 11g is focused on the correlation of multiple columns of single table, not join correlation.

---

Dion Cho - Oracle Performance Storyteller

http://dioncho.wordpress.com (english)
http://ukja.tistory.com (korean)

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On Sat, Mar 7, 2009 at 1:31 AM, Riyaj Shamsudeen <riyaj.shamsudeen_at_gmail.com
> wrote:

> Hrishys
>
> You can read all about correlation in my blog below. BTW, 11g provides
> some relief with extended stats. Dynamic sampling at higher level also can
> provide some relief for columns with higher correlation.
>
>
> http://orainternals.wordpress.com/2008/03/21/correlation-between-column-predicates/
>
> http://orainternals.wordpress.com/2008/12/19/correlation-nocorrelation-and-extended-stats/
>
> But, do you have any index on (SRC, TF ,CDT)? That might make hash join
> plan cheaper and CBO might choose it.. Just a guess :-)
>
>
> --
> Cheers
>
> Riyaj Shamsudeen
> Principal DBA,
> Ora!nternals - http://www.orainternals.com
> Specialists in Performance, Recovery and EBS11i
> Blog: http://orainternals.wordpress.com
>
>
>
> On Fri, Mar 6, 2009 at 10:02 AM, Allen, Brandon <Brandon.Allen_at_oneneck.com
> > wrote:
>
>> A common example of correlated join criteria would be:
>>
>> select . . .
>> where make='FORD'
>> and model='MUSTANG';
>>
>> The CBO doesn't know that all Mustangs are built by Ford, so it's not
>> aware that the extra filter condition won't really filter out any more rows.
>>
>> Regards,
>> Brandon
>>
>> -----Original Message-----
>> From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org]
>> On Behalf Of hrishy
>>
>> I didnt quite understand the statement
>> "Check if the join criteria between SC and SH are correlated"
>>
>>
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>
>
>
>

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Received on Fri Mar 06 2009 - 23:08:35 CST