Re: Why would an index not be used if specified as a hint in a query?

From: Mark Bole <makbo_at_pacbell.net>
Date: Sun, 13 Feb 2005 23:47:01 GMT
Message-ID: <VFRPd.4688$aW6.3547@newssvr22.news.prodigy.net>

Galen Boyer wrote:

> On Sat, 12 Feb 2005, niall.litchfield_at_dial.pipex.com wrote:
>

[...]

>>
>>Using an INDEX hint *WILL* cause the index to be used *IF IT CAN BE* 

>
>
> I thought hints lowered the cost of a particular access path. Therefore
> the CBO was more apt to pick it. But, that a hint was nothing more than
> that. I didn't think there was anyway to "expect" that a hint was going
> to be obeyed.
>

[...]

But isn't an outline (plan stability) just a collection of hints -- implying that they *are* obeyed by CBO if possible?

Must admin, though, I'm still having a hard time fully understanding all the implications of the following statement at:

http://download-west.oracle.com/docs/cd/B14117_01/server.101/b10752/outlines.htm#25949

"When Oracle creates an outline, plan stability examines the optimization results using the same data used to generate the execution plan. That is, Oracle uses the input to the execution plan to generate an outline, and not the execution plan itself."

-Mark Bole Received on Sun Feb 13 2005 - 17:47:01 CST