Windows uses the MAC address in GUID generation.
> -----Original Message-----
> From: pgsql-general-owner@postgresql.org [mailto:pgsql-general-
> owner@postgresql.org] On Behalf Of Scott Marlowe
> Sent: Wednesday, July 27, 2005 1:47 PM
> To: John DeSoi
> Cc: Tino Wildenhain; Riaan van der Westhuizen; Postgresql-General
> Subject: Re: [GENERAL] GUID for postgreSQL
>
> On Wed, 2005-07-27 at 15:32, John DeSoi wrote:
> > On Jul 27, 2005, at 4:49 AM, Tino Wildenhain wrote:
> >
> > > I'd create a sequence:
> > >
> > > CREATE SEQUENCE global_unique_id_seq;
> > >
> > > and a function:
> > >
> > > CREATE OR REPLACE FUNCTION newid()
> > > RETURNS text AS
> > > $BODY$ SELECT nextval('global_unique_id_seq')::text; $BODY$
> > > LANGUAGE 'sql' VOLATILE;
> > >
> > >
> > > now every call to newid() returns a garantied unique id for
> > > say the next 18446744073709551616 calls.
> > > Of course you can obfuscate the ID even more using
> > > md5, include servername and so on, but this will not improve
> > > security in any way (unless you mix data with 2nd database)
> >
> >
> > This is not really a viable replacement for a GUID == globally
unique
> > identifier. Here global means that if I use the application in
> > multiple databases, I'm guaranteed that no two identifiers will be
> > the same. Using a sequence will only support uniqueness for a single
> > database.
>
> So, how can two databases, not currently talking to one another,
> guarantee that their GUIDs don't collide? using a large randomly
> generated name space only reduces the chances of collision, it doesn't
> actually guarantee it.
>
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