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List:       mysql
Subject:    Re: Cost of using over dimensioned columns
From:       Olaf Stein <olaf.stein () nationwidechildrens ! org>
Date:       2009-02-25 18:27:25
Message-ID: C5CAF7BD.E842%olaf.stein () nationwidechildrens ! org
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Morten,

Check out
http://dev.mysql.com/doc/refman/5.1/en/storage-requirements.html

For example, the cost of longtext (L+4 bytes) over mediumtext (L+3 bytes) is
1 byte per record. If you have a lot of records this might be significant.

In the case of varchar it is similar, L+1 if less than 255 bytes, L+2 if
more.

In general it is good practice to define columns types as tight as possible,
if you have a username field and you do not want more than 25 characters
long username, you would define username varchar(25).

Olaf



On 2/25/09 11:52 AM, "Morten" <my.lists@mac.com> wrote:

> Hi list,
> 
> I'm wondering what the "cost" (if any) is by using eg. mediumtext
> over  text, or largetext over mediumtext. Is there a non-negligible
> reason to not just just  largetext?
> 
> And how about varchars, what's the "cost" of using varchar(1000)
> rather than varchar(20)?
> 
> My intuition tells me that I should keep things as tight as possible,
> but I may be narrow minded and need a sanity check.
> 
> Thanks!
> 
> Morten
> 
> 

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