RE: oracle can ignore hints

  • From: "Bobak, Mark" <Mark.Bobak@xxxxxxxxxxxxxxx>
  • To: <oracle-l@xxxxxxxxxxxxx>
  • Date: Thu, 4 Mar 2004 16:03:27 -0500

Wow, that's a surprise.  I've never run into a case where a properly specified 
hint was not used.  I have always been of the view that a hint was a directive, 
and that if it was well-formed, it would not be ignored.
April, do you have a reproducible test case of the situation you described?

-----Original Message-----
From: April Wells [mailto:AWells@xxxxxxxxxx]
Sent: Thursday, March 04, 2004 2:45 PM
To: 'oracle-l@xxxxxxxxxxxxx'
Subject: RE: oracle can ignore hints

Yep, they are 'friendly suggestions' that the CBO can simply choose to ignore 
if it thinks it knows better than you. 

We have one query that we have hinted, we have computed statistics, we have 
built histograms, we have jumped through hoops... the only way to force it to 
use an index is to Never analyze that index and to hope, then, that the CBO 
makes the right assumptions.

April Wells 
Oracle DBA/Oracle Apps DBA 
Corporate Systems 
Amarillo Texas 
"Few people really enjoy the simple pleasure of flying a kite" 
Adam Wells age 11 
"Imagination is the highest kite one can fly." 
Lauren Bacall 

-----Original Message----- 
From: ryan.gaffuri@xxxxxxx [ mailto:ryan.gaffuri@xxxxxxx] 
Sent: Thursday, March 04, 2004 12:44 PM 
To: oracle-l@xxxxxxxxxxxxx 
Subject: oracle can ignore hints 

We had a discussion on here regarding hints. some of you stated that Oracle 
cannot ignore a proper hint. I have a TAR open and asked about this. Here is 
the response.

"A hint simply adds weight to a cost estimation, it can still be overridden by 
the CBO if the values aren't seen as useful."

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