Valentin Bogdanov schrieb:
--- On Mon, 11/8/08, Gregory Stark <stark@xxxxxxxxxxxxxxxx> wrote:
From: Gregory Stark <stark@xxxxxxxxxxxxxxxx>
Subject: Re: [PERFORM] Using PK value as a String
To: "Jay" <arrival123@xxxxxxxxx>
Cc: pgsql-performance@xxxxxxxxxxxxxx
Date: Monday, 11 August, 2008, 10:30 AM
"Jay" <arrival123@xxxxxxxxx> 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
UUID is already a surrogate key not a natural key, in no aspect better
than a numeric key, just taking a lot more space.
So why not use int4/int8?
