To: okparanoid@free.fr
cc: pgsql-performance@postgresql.org
Subject: Re: determining maxsize for character varying 
In-reply-to: <1181987590.4673b306d4baf@imp.free.fr> 
References: <1181987590.4673b306d4baf@imp.free.fr>
Comments: In-reply-to okparanoid@free.fr
	message dated "Sat, 16 Jun 2007 11:53:10 +0200"
Date: Sat, 16 Jun 2007 11:07:08 -0400
Message-ID: <11149.1182006428@sss.pgh.pa.us>
From: Tom Lane <tgl@sss.pgh.pa.us>

okparanoid@free.fr writes:
> Hello i would like to know if not determining a max size value for a
> character varying's fields decrease the perfomance (perhaps size of
> stockage ?

No, more the other way around: specifying varchar(N) when you had to
pick N out of the air decreases performance, because of all the
essentially useless checks of the string length that Postgres has to
make.  If you cannot defend a specific limit N as being required by your
application, then just make it unconstrained varchar (or better text).

Do *not* use char(N) for data with highly variable width; that one
definitely will cost you performance and disk space.

			regards, tom lane