Re: Number of Columns in a Table & SQL Performance ?

From: Greg Rahn <>
Date: Mon, 9 Mar 2009 14:22:25 -0700
Message-ID: <>

First I have to ask myself, what (good) relational database design for an OLTP system would lead normalized tables having 200 columns.

Second, I would think about buffer cache efficiencies. The wider the table the less rows that fit in a block. Given that most OLTP applications rarely need access to all the columns in a table it would seem to me that having a 200, let alone 400 column table would lead to having lots of data in the buffer cache that is not used and thus result in either a reduced buffer cache efficiency (causing more than desired physical I/O) or having to compensate by having a very large db cache full of rows whose columns are not accessed.

Perhaps you could share what are the perceived benefits from merging the two tables?

On Mon, Mar 9, 2009 at 6:19 AM, VIVEK_SHARMA <> wrote:
> Does the number of columns in a table affect the performance of
> If so, why?
> NOTE - Merge of 2 existing tables each has 200 columns approx into a single
> Table is being planned..

Received on Mon Mar 09 2009 - 16:22:25 CDT

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