Re: DWH varchar2(4000)

From: Dave Morgan <>
Date: Wed, 24 Dec 2014 12:34:40 -0700
Message-ID: <>

On 12/24/2014 12:02 PM, Mark W. Farnham wrote:
> " No, it was taught to me in the early 90s as part of a formal Data
> Modelling course. I am pretty sure it is/was standard practise in the old
> mainframe databases (IMS? IDMS?, it's been a long time :) It is not database
> design, it is data modelling."
> 1) Your argument seems to be that because it was taught, therefore it is
> valid.

I never argued that. I was asked a question and provided an answer. My argument is that standard sizes enhance productivity in the development process, and improve production availability.

> number of allowed sizes. Regarding database modelling for modern systems it
> would be peachy to use a generous max when domain set limitations are
> unclear IF it were not the case there are known side effects (that are
> significantly negative) when a row can not a priori be known to fit in a
> single block. (That's no appeal to authority; test results and a recipe book
> for you to repeat the tests yourself are conveniently in this very thread).

Theoretically yes, however, in the real world most table rows will either fit easily into a block despite the column definitions or will not come close to fitting in a single block if all the fields are complete and of maximum size.

There is no ROI in the modelling custom column sizes unless there is an impact on the client. So once the app is tuned, the database access is tuned, and the queries are tuned, and you still have insert/update performance issues then it is time to re-model.


Dave Morgan
Senior Consultant, 1001111 Alberta Limited
403 399 2442
Received on Wed Dec 24 2014 - 20:34:40 CET

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