Re: Init.ora .. OPTIMIZER parm: optimizer_index_cost_adj

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.

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

 Have you tried increasing the hash_area_size, or db_file_multiblock_read_count? 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:

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
>
>
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