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Re: performance cost for varchar(20), varchar(255), and text

From: Shane Ambler <pgsql(at)Sheeky(dot)Biz>
To: Jessica Richard <rjessil(at)yahoo(dot)com>
Cc: pgsql-admin(at)postgresql(dot)org
Subject: Re: performance cost for varchar(20), varchar(255), and text
Date: 2008-07-05 16:27:58
Message-ID: 486FA10E.3040004@Sheeky.Biz (view raw or whole thread)
Lists: pgsql-admin
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 -
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.


Shane Ambler
pgSQL (at) Sheeky (dot) Biz

Get Sheeky @ http://Sheeky.Biz

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