Re: Reorg to put columns in order

Hi Mark and list,

My old article is still at
http://www.ixora.com.au/tips/table_column_order.htm

However, the impact of column order on fetching a value from a row was greatly reduced at 10g. My column 1 v column 10 example now typically returns a difference of only 1% to 2%.

@   Regards,
@   Steve Adams
@   http://www.ixora.com.au/         - For DBAs
@   http://www.christianity.net.au/  - For all

-----Original Message-----
Subject: RE: Reorg to put columns in order Date: Tue, 23 Oct 2007 13:13:40 -0400
From: "Powell, Mark D" <mark.powell_at_eds.com> To: <oracle-l_at_freelists.org>

>
> Steve Adams had an article on his website about the cost of retrieving
> columns to the right years ago. I think he had recommended placing the
> most retrieved columns at the start of the row. If the article is still
> posted it would be interesting to compare the two. Another thing to add
> to my endless list.
>
> -----Original Message-----
> From: Gints Plivna
> Sent: Tuesday, October 23, 2007 10:40 AM
> To: ric.van.dyke_at_hotsos.com
> Cc: Jacob.van.Zanen_at_rabobank.com; oracle-l_at_freelists.org
> Subject: Re: Reorg to put columns in order
>
> OK according to presentation by Joze Senegacnik he gave in OOW 2006:
> "It is interesting that the cost of LIO depends of the position of the
> column retrieved."
> He shows in his presentation's example that query elapsed time increases
> for the 250th column compared to 1st column. 250th column of course is
> just an example. The actual example forces full scan on the table and
> the growth is ~50% for 250th column compared to 1st column.
> Also CBO increases CPU cost as the column number grows.
> Unfortunately it seems that these presenations are not available for
> download any more, so you may ask details to the author himself :) He is
> (at least WAS) member of this list.
>
> However the main question remains - do these arguments justify the cost
> of reorganization? (somehow I doubt that these arguments even appeared
> in the real discussion :)
>
> Gints Plivna
> http://www.gplivna.eu

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