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Re: Index skip scan

From: fairlie rego <fairlie_r_at_yahoo.com>
Date: Tue, 20 Sep 2005 23:02:20 -0700 (PDT)
Message-ID: <20050921060220.2217.qmail@web31904.mail.mud.yahoo.com>


Hi,  

Due to the following bugs your best bet is to use the INDEX_SS hint as mentioned by Mladen before  

3354231Index skip scan is sometimes estimated at very high cost fixed in 9206

4050226Index skip scan may not be chosen when it is a good choice fixed in 9207  

Regards,
Fairlie

The Human Fly <sjaffarhussain_at_gmail.com> wrote: Index skip scans improve index scans by nonprefix columns. Skip scanning lets a composite index be split logically into smaller subindexes. In the skip scanning, the initial column of the composite index is not specified in the query.
Number of logical subindexes is determined by the number of distinct values in the initial column. Skip scanning is advantageous if there are few distinct values in the leading column of the composite index and many distinct values in the nonleading key of the index.

On 9/20/05, Hameed, Amir wrote:
>
>
> Folks,
> Does anyone know that in order for the optimizer to choose "Index skip scan"
> on a concatenated index where the first column is not very selective but the
> second one is, approximately what type of selectivity on the leading column
> the Optimizer look for before deciding to take this route?
>
> Thanks
> Amir

-- 
Best Regards,
Syed Jaffar Hussain
OCP 8i & 9i DBA,
Banque Saudi Fransi,
Saudi Arabia
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Fairlie Rego
Senior Oracle Consultant
Optus Telecommunications
www.optus.com.au
Mobile: +61 4 02 792 405
Home: +61 2 8920 0273

 
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Received on Wed Sep 21 2005 - 01:04:32 CDT

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