Re: Init.ora .. OPTIMIZER parm: optimizer_index_cost_adj

From: Tim Sawmiller <sawmillert_at_state.mi.us>
Date: Wed, 31 Jan 2001 13:10:59 -0500
Message-Id: <10758.127918@fatcity.com>

Get used to it...there are several parameters that affect the Optimizer's = thinking/biases. Change/add parameters with great care, preferably = testing the change against some key explain plans of heavy impact SQL. =20

>>> chuck_hamilton_at_yahoo.com 01/31/01 12:20PM >>>

 Have you tried increasing the hash_area_size, or db_file_multiblock_read_c= ount? I've found altering these at the session level sometimes makes the = optimizer prefer a hash_join, though not always. Sometimes I wonder where = it's brain is.

  jkstill_at_cybcon.com wrote:=20

I've used this in an attempt to make the optimizer prefer a hash join over a nested loops join.

The desired results were not achieved.

Jared

On Tue, 30 Jan 2001 bruce.taneja_at_mcd.com wrote:

>
>
> Has any one messed with
> optimizer_index_cost_adj
> on 8.1.7 ??
>
> The default is 100, but my boss thinks 10 is a better value for Cost =
based Opmtzr..
> doesn't make any sense to me.. why would reducing the cost of using an
> optimizer make it more CBO or go faster.. what if its a large table?
>
> Is it a good strategy to reduce this value to 10 or so ..
>
> any one played with this on a 30GB database ? or any other size db?
>
> thanks, Bruce
>
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.com=20
> --
> Author:
> INET: bruce.taneja_at_mcd.com=20
>
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--=20
Please see the official ORACLE-L FAQ: http://www.orafaq.com=20 --=20
Author:=20
INET: jkstill_at_cybcon.com=20

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