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Home -> Community -> Mailing Lists -> Oracle-L -> RE: Reorg to put columns in order
Sorry that I'm coming to this discussion late but I do want to point out
that column order actually does mater. However it's not in the way
these folks are thinking. When the data is stored in the block, each
rows data is stored in the column order of the table definition. Why
this is important is that trailing NULL columns will actually take up NO
SPACE in the row, however NULL columns between non-null columns will
take up a byte of storage. OK so one byte isn't a big deal, unless you
are talking about millions of rows with maybe several null columns
within each row. Now it may actually add up to something.
The reality is that column order does mater from a space management point of view, if you have columns that are nearly always null, then they should be at the end of the table definition. If not you are "wasting" some space within each row. Is it enough to make a difference? That will be your call.
Ric Van Dyke
Hotsos Enterprises
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Zanen van, J (Jacob)
Sent: Monday, October 22, 2007 2:00 AM
To: oracle-l_at_freelists.org
Subject: Reorg to put columns in order
Hi All,
I'm having a bit of an issue with our designers/developers for our so called "datawarehouse"
Columns are added to tables every so often based on requirements from the business. They however insist on doing a reorg to get the columns in a certain order so when they pull them up in BO the columns show up in an order that makes sense to them. I have raised my doubts about this procedure as it takes a 2 second job and squeezes it in a 7 hour job.
I can see from a chained/migrated row point of view that there might be a valid reason for it but since they have always done it this I see no way for me to find out how bad this is going to be. I suspect for most of these tables it won't make much difference as they are not filled with data for historical records AFAIK.
My solution for them was to create a view on top of the table but they rejected the idea and insist this is the way to go.
Anybody have any insight for me.
Thnx
Jack
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-- http://www.freelists.org/webpage/oracle-lReceived on Tue Oct 23 2007 - 08:12:32 CDT
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