Re: Index Cost Calculation Mystery

thanks a lot to all of you who worked on this issue, especially Jonathan Lewis.

He wrote an excellent blog entry describing the reason for this behavior in this case.
http://jonathanlewis.wordpress.com/2013/07/12/wrong-index-2-2/

Best regards
Martin Klier

Martin Klier schrieb:

> The Optimizer chooses IDX2_AUFTRAG for the index range scan, but I can't
> explain why. The 10053 trace tells:
> ======10053==========
> Access Path: index (RangeScan)
> Index: IDX2_AUFTRAG
> resc_io: 186.00 resc_cpu: 1585830
> ix_sel: 0.000034 ix_sel_with_filters: 0.000034
> Cost: 94.49 Resp: 94.49 Degree: 1
> Access Path: index (AllEqRange)
> Index: IDX7_AUFTRAG
> resc_io: 1027.00 resc_cpu: 8999338
> ix_sel: 0.000241 ix_sel_with_filters: 0.000241
> Cost: 521.97 Resp: 521.97 Degree: 1
> ...
> ...
> Best:: AccessPath: IndexRange
> Index: IDX2_AUFTRAG
> Cost: 94.49 Degree: 1 Resp: 94.49 Card: 0.00 Bytes: 0
> ======10053==========
>
> But why is the cost of a AllEqRange on a single column index
> (IDX7_AUFTRAG) 521.97 and an index range scan on a multi-column index
> (IDX2_AUFTRAG) has only cost 94.49?

-- 
Usn's IT Blog for Oracle and Linux
http://www.usn-it.de


-- 
Usn's IT Blog for Oracle and Linux
http://www.usn-it.de

--
http://www.freelists.org/webpage/oracle-l