Re: Index question

From: Mark Richard <mrichard_at_transurban.com.au>
Date: Wed, 25 Jun 2003 16:47:36 -0700
Message-ID: <F001.005B9ED6.20030625161017@fatcity.com>

Teresita,

I don't fully understand whether adding or removing a hint caused the problem but like Stephane said - you should probably stay away from them for now. If adding a hint decreased performance then you have proved this for yourself.

A couple of important points:

Using an index isn't always faster than scanning the table
If a database is correctly analyzed then the optimisor can determine when to use indexes or not automatically
Hints can force the optimisor to choose a non-optimal execution plan. If you are smarter than the optimisor this may be fine but in most cases the optimisor will make the right decision when all tables are analyzed
Hints have very specific formatting and object name rules. If you rename an index the hint will become invalid and be blissfully ignored - you won't even know.
There are some hints which can safely be used but it takes a good understanding of Oracle first. My advice would be don't use them. If you have a specific problem then post lot's of details here and someone might suggest trying a hint.
Until you really understand the implications of using a specific hint it can be dangerous in terms of performance - Stephane is not lying when he says you can do more harm than good. I have many cases where I can "tune" a query simply by removing the hints which someone included and letting Oracle do what it does best.

Regards,

Mark.

                                                                                       
                                                 
                      "Teresita Castro"                                                
                                                 
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                      26/06/2003 09:29                                                 
                                                 
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Ophss...I have a terrible problem, I am using VB with Oracle and since we put that instruccion on the execute instruction our execution time decrease.

The problem is that my boss was the one that found that instruction and I have to told her not to uses it, but with her I have to show some evidence that show why now to uses hits.

Do you have any information that I can show to her.

Thanks!!!

>>> [EMAIL PROTECTED] 06/25/03 02:34PM >>> Teresita,

Since you advertise yourself as a newbie, listen to an old-timer : for the next two years, forget about hints. You risk doing more harm than good.

--
Regards,

Stephane Faroult
Oriole Software
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Author: Stephane Faroult
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Received on Wed Jun 25 2003 - 18:47:36 CDT