Re: SQL code tuuning

Niall,

When i meant that the RBO is not based on sound logic this is what i mean

when i say select * from table a , table b where blah blah

I expect it to be the **same** as

select * from table b, table a blah blah blah

Agreed , that in a CBO too, sometimes the Order matters (When the optimizer cannot choose a proper driving table) or when you use the Ordererd hint. But its based on a much more sounder logic .

"Niall Litchfield" <n-litchfield_at_audit-commission.gov.uk> wrote in message news:<3bcbf163$0$237$ed9e5944_at_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.
Received on Thu Oct 18 2001 - 05:47:56 CDT