Does a varchar field's declared size have any impact in PostgreSQL?

Question

Is VARCHAR(100) any better than VARCHAR(500) from a performance point of view? What about disk usage?

Talking about PostgreSQL today, not some database some time in history.

Answer 1

They are identical.

From the PostgreSQL documentation:

http://www.postgresql.org/docs/8.3/static/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.

Here they are talking about the differences between char(n), varchar(n) and text (= varchar(1G)). The official story is that there is no difference between varchar(100) and text (very large varchar).

Answer 2

There is no difference between varchar(m) and varchar(n)..

http://archives.postgresql.org/pgsql-admin/2008-07/msg00073.php

There is a difference between varchar(n) and text though, varchar(n) has a built in constraint which must be checked and is actually a little slower.

http://archives.postgresql.org/pgsql-general/2009-04/msg00945.php