RE: oracle can ignore hints

Don't know how reproducible... the table is horrendously skewed with regards
to histograms and the query is a 7 table join...  
 
I can get full details from the lady doing the analysis if you like.  It
isn't pretty.
 

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: Bobak, Mark [mailto:Mark.Bobak@xxxxxxxxxxxxxxx]
Sent: Thursday, March 04, 2004 3:03 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: RE: oracle can ignore hints


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?
 
-Mark

-----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
<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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