Re: Bitmap index costing - how to influence

  • From: Randolf Geist <info@xxxxxxxxxxxxxxxxxxxxx>
  • To: oracle-l@xxxxxxxxxxxxx
  • Date: Sat, 28 Mar 2009 22:10:03 +0100

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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