From: Lew <lew@lwsc.ehost-services.com>
To: pgsql-admin@postgresql.org
Subject: Re: performance cost for varchar(20), varchar(255), and text
Date: Sat, 05 Jul 2008 11:04:53 -0400
Message-ID: <p9WdnYHPPPgIEPLVnZ2dnUVZ_tydnZ2d@comcast.com> (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
Interestingly, the Postgres documentation has the answer:
<http://www.postgresql.org/docs/8.3/interactive/datatype-character.html;
> 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.
Performance is not the only issue. The semantics of CHAR and VARCHAR differ.
You cannot use them equivalently.
I recommend searching the docs as a first approach to finding such answers.
--
Lew
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Subject: Re: performance cost for varchar(20), varchar(255), and text
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