Re: Index skip scan
- From: The Human Fly <sjaffarhussain@xxxxxxxxx>
- To: Amir.Hameed@xxxxxxxxx
- Date: Wed, 21 Sep 2005 08:55:32 +0300
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 <Amir.Hameed@xxxxxxxxx> 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
----------------------------------------------------------------------------------------
"It is your atittude, not your aptitude that determins your altitude."
--
//www.freelists.org/webpage/oracle-l
Other related posts:
