Re: CBO: Extensions and/or Multi Column Indexes

In addition to Jonathan's and Chinar's reply - even if you have extended statistics they might not be used in first place if you work with histograms on the involved basic columns (e.g. fix_control 6972291).

Best Regards
Stefan Koehler

Independent Oracle performance consultant and researcher Website: http://www.soocs.de
Twitter: _at_OracleSK

> Martin Klier - Performing Databases GmbH <martin.klier_at_performing-db.com> hat am 9. Januar 2019 um 11:25 geschrieben:
>
>
> Hi listers,
>  
> happy new year to all of you!
>  
> I was wondering if it is useful to still have manually created extended statistics (to enhance cardinality calculation for logically connected columns) and multi-column indexes of the same columns at the same time.
> I need the two- or three-column indexes for query performance reasons anyway, so leaving them out is not an option.
>  
> My question is, does it make sense to manually create extended statstics for two columns, that are already part of a two-column index?
> My field of using this stuff is versions 11.2, 12.1, 12.2 and 18.3 on Linux.
>  
> Background: I can't see an extension in dba_stat_extensions if I do not have the extended stats created, so I was thinking, if the CBO can calculate the correct cardinality from the index / index stats, I could spare my stats jobs the effort to calculate many of my virtual column stats.
>  
> Thank you in advance, and please don't laugh if I am way off the path... :)
>  
> Best regards
>
> --
> Martin Klier // Performing Databases GmbH
> Managing Partner // Senior DB Consultant
> Oracle ACE Director
>
> martin.klier_at_performing-db.com // https://www.performing-databases.com

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