From: Shane Ambler <pgsql@Sheeky.Biz>
To: Jessica Richard <rjessil@yahoo.com>
Cc: pgsql-admin@postgresql.org
Subject: Re: performance cost for varchar(20), varchar(255), and text
Date: Sun, 06 Jul 2008 01:57:58 +0930
Message-ID: <486FA10E.3040004@Sheeky.Biz> (raw)
In-Reply-To: <801541.60585.qm@web56406.mail.re3.yahoo.com>
References: <801541.60585.qm@web56406.mail.re3.yahoo.com>
Jessica Richard wrote:
> I am tuning a database created by someone else.
>
> I noticed that some column lengths were defined longer than needed.
>
> For example, an Id column is holding a stand length of 20 characters
> but was defined as varchar(255).
>
> On some other columns, for example, a Description column is supposed
> to hold less than 100 characters but defined as text.
>
> I am trying to understand the performance impact if a column is over
> defined in the following cases:
>
> 1. char(20) vs varchar(20)
>
> 2. varchar(20) vs varchar(255)
>
> 3. varchar(255) vs text
>
>
> thanks, Jessica
>
From the manual -
<quote>
Tip: There are no performance differences between these three types,
apart from increased storage size when using the blank-padded type, and
a few extra cycles to check the length when storing into a
length-constrained column. While character(n) has performance advantages
in some other database systems, it has no such advantages in PostgreSQL.
In most situations text or character varying should be used instead.
</quote>
http://www.postgresql.org/docs/8.3/static/datatype-character.html
--
Shane Ambler
pgSQL (at) Sheeky (dot) Biz
Get Sheeky @ http://Sheeky.Biz
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To: pgsql-admin@postgresql.org
Cc: pgsql@Sheeky.Biz, rjessil@yahoo.com
Subject: Re: performance cost for varchar(20), varchar(255), and text
In-Reply-To: <486FA10E.3040004@Sheeky.Biz>
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