Re: Cost of Access Plan using Bitmap Indexes

From: Tanel Poder <change_to_my_first_name_at_integrid.info>
Date: Fri, 22 Aug 2003 20:34:29 +0300
Message-ID: <3f465427$1_1@news.estpak.ee>

> I tried to create a bitmap index on this single column. the optimizer
> did not choose it so I did force it with an hint. the cost was 356000
>
> tried it anyway and the query completed in seconds.
>
> Table and indexes are all analyzed!!!
>
> I am studying the doc on the Optimizer right now but can anyone please
> give me a hint of where to look to understand this situation??

I assume you've already checked the differences in execution plans?

The most useful thing in understanding and tuning CBO behaviour is event 10053 trace.

Type:

alter session set events '10053 trace name context forever, level 1'; then run your (slow) query
check udump for trace file and it's contents should show where overly high cost estimations are coming from.

Tanel. Received on Fri Aug 22 2003 - 12:34:29 CDT