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

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

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