Re: [PERFORM] Using PK value as a String

--- On Mon, 11/8/08, Gregory Stark <stark@enterprisedb.com> wrote:

> From: Gregory Stark <stark@enterprisedb.com>
> Subject: Re: [PERFORM] Using PK value as a String
> To: "Jay" <arrival123@gmail.com>
> Cc: pgsql-performance@postgresql.org
> Date: Monday, 11 August, 2008, 10:30 AM
> "Jay" <arrival123@gmail.com> writes:
>
> > I have a table named table_Users:
> >
> > CREATE TABLE table_Users (
> > UserID character(40) NOT NULL default
> '',
> > Username varchar(256) NOT NULL default
> '',
> > Email varchar(256) NOT NULL default
> ''
> > etc...
> > );
> >
> > The UserID is a character(40) and is generated using
> UUID function. We
> > started making making other tables and ended up not
> really using
> > UserID, but instead using Username as the unique
> identifier for the
> > other tables. Now, we pass and insert the Username to
> for discussions,
> > wikis, etc, for all the modules we have developed. I
> was wondering if
> > it would be a performance improvement to use the 40
> Character UserID
> > instead of Username when querying the other tables, or
> if we should
> > change the UserID to a serial value and use that to
> query the other
> > tables. Or just keep the way things are because it
> doesn't really make
> > much a difference.
>
> Username would not be any slower than UserID unless you
> have a lot of
> usernames longer than 40 characters.
>
> However making UserID an integer would be quite a bit more
> efficient. It would
> take 4 bytes instead of as the length of the Username which
> adds up when it's
> in all your other tables... Also internationalized text
> collations are quite a
> bit more expensive than a simple integer comparison.
>
> But the real question here is what's the better design.
> If you use Username
> you'll be cursing if you ever want to provide a
> facility to allow people to
> change their usernames. You may not want such a facility
> now but one day...
>

I don't understand Gregory's suggestion about the design. I thought using natural primary keys as opposed to surrogate ones is a better design strategy, even when it comes to performance considerations and even more so if there are complex relationships within the database.

Regards,
Valentin

> --
> Gregory Stark
> EnterpriseDB http://www.enterprisedb.com
> Ask me about EnterpriseDB's On-Demand Production
> Tuning
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