Re: Bitmap index costing - how to influence
- From: Christo Kutrovsky <kutrovsky.oracle@xxxxxxxxx>
- To: info@xxxxxxxxxxxxxxxxxxxxx
- Date: Sat, 28 Mar 2009 17:46:38 -0400
Thanks Randalf,
I can't modify the query, and I've set this globally for the database
already as a workarround.
However this affects costing calculations for b-tree indexes.
I am looking for something that affects only bitmaps, and ideally only
specific bitmap indexes.
On Sat, Mar 28, 2009 at 5:10 PM, Randolf Geist
<info@xxxxxxxxxxxxxxxxxxxxx> wrote:
> Chris,
>
> if you can influence the query, then you can try to lower the cost of the
> bitmap index access specifically to that query by using the (undocumented)
> OPT_PARAM hint introduced in 10g:
>
> select /*+ opt_param('optimizer_index_cost_adj', 10) */ ...
>
> If you can't modify the query but the query is static, you could apply this
> hint using Stored Outlines or SQL profiles in 10g.
>
> Regards,
> Randolf
>
> Oracle related stuff blog:
> http://oracle-randolf.blogspot.com/
>
> SQLTools++ for Oracle (Open source Oracle GUI for Windows):
> http://www.sqltools-plusplus.org:7676/
> http://sourceforge.net/projects/sqlt-pp/
>
>> I am pretty much stuck on a bitmap costing problem.
>>
>> Any ideas on how to influence bitmap index cost, relative to full
>> table scan cost? Anything goes as long as it doesn't break b-tree
>> index costing.
>>
>> - optimizer_index_cost_adj - i will have to set this to 10 (10 times
>> cheaper) for bitmaps to be used. I am concerned about proper
>> calculations of b-tree indexes vs full table scans
>>
>> Any other ideas?
>
>
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--
Christo Kutrovsky
Senior DBA
The Pythian Group - www.pythian.com
I blog at http://www.pythian.com/blogs/
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