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
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Shane Ambler
pgSQL (at) Sheeky (dot) Biz
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