Re: SQL code tuning

From: Niall Litchfield <n-litchfield_at_audit-commission.gov.uk>
Date: Tue, 16 Oct 2001 09:35:23 +0100
Message-ID: <3bcbf163$0$237$ed9e5944@reading.news.pipex.net>

"mark" <mark_brehmen_at_yahoo.com> wrote in message news:fa4781e4.0110150103.73725d0_at_posting.google.com...
> But, maybe i am reading the wrong documentation . I have 8i in which
> CBO has become popular.
> My experience wiht Rule based optimizer is - its best to be avoided. I
> have seen **dramatic*** differences in "Explain Plan" output by just
> Rearranging the columns of the "From" Clause.

I on the other hand have seen query time go from 10 secs to 35 minutes just by adding 13 rows to a table when using CBO. There are advantages and disadvantages to both.

>Its a mess to work with
> the RBO, because its not based on any sound logic.

The RBO is based on sound logic (though that logic may not always be apparent to us mere mortals <g>). A much better reason for not using it is that it does not support any of the new Oracle features that have come in since it was desupported. Like objects,partitioning,IOTs, bitmapped indices etc.

--
Niall Litchfield
Oracle DBA
Audit Commission UK

Received on Tue Oct 16 2001 - 03:35:23 CDT