Re: The optimizer is ignoring my hints

  • From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
  • To: <oracle-l@xxxxxxxxxxxxx>
  • Date: Mon, 24 May 2004 22:22:35 +0100

Clearly you haven't yet discovered the 

So if you include this hint as an embedded hint,
does Oracle ignore it ?

I haven't tested the parameter yet - but here's another
interesting thought. Oracle Corp. includes hidden boolean 
parameters so that they can be changed in some future release.
They must be getting confident.

In answer to your previous question - I think this hint, and
the description of the parameter, gives the clue about 
profiles, and outlines - the only hints ignored are the
embedded ones (i.e. the ones you put in the SQL), the
one stored in the database for a query still apply.
(I've only tested this for outlines, though).


Jonathan Lewis
The Co-operative Oracle Users' FAQ
Optimising Oracle Seminar - schedule updated May 1st

----- Original Message ----- 
From: "Niall Litchfield" <niall.litchfield@xxxxxxxxx>
To: <oracle-l@xxxxxxxxxxxxx>
Sent: Monday, May 24, 2004 11:37 AM
Subject: The optimizer is ignoring my hints

Yes I know we did this to death a little while back - I believe that I
may have said words to the effect that the CBO never *ignores* valid
hints but that you may not get the execution plan you expect if you
don't specify enough.

Consider the following 10053 extracts using the same old scott/tiger demo

The difference between them - a new parameter for 10g

  _optimizer_ignore_hints             = true

So it would seem that having just about settled the whole the
optimizer is ignoring my hint debate - now it can.

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