Re: Fwd: Re: Really deleting system statistics?

From: Peter Alteheld <palteheld_at_yahoo.de>
Date: Thu, 12 May 2005 08:47:07 +0200 (CEST)
Message-ID: <20050512064707.49162.qmail@web26504.mail.ukl.yahoo.com>

Well, I see different costs in 10g, when I have no system statistics and switch optimizer models.  

For example: do a full table scan with select count(object_id) from big_table (table from Tom Kyte's Effective Oracle by Design) - with IO model costs=5630, with CPU model costs = 13065 Peter

amit poddar <amit.poddar_at_yale.edu> wrote: I thought Oracle would use the IO model in absence of system statistics (default behaviour in 9i) ?

thanks
amit

Peter Alteheld wrote:

>Hi,
>
>I wanted to learn about the cpu model behaviour when no system statistics are available. That is different from the io model.
>
>Peter
>amit poddar wrote:
>How about settting
>
>_optimizer_cost_model to *io
>
>SQL> alter session set "_optimizer_cost_model"=abc;
>ERROR:
>ORA-00096: invalid value ABC for parameter _optimizer_cost_model, must
>be from
>among choose, io, cpu
>
>
>
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Received on Thu May 12 2005 - 02:51:39 CDT