smarlowe@g2switchworks.com (Scott Marlowe) writes:
> 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.
Consult RFC 4122...
<http://www.ietf.org/rfc/rfc4122.txt>
"Abstract
This specification defines a Uniform Resource Name namespace for
UUIDs (Universally Unique IDentifier), also known as GUIDs (Globally
Unique IDentifier). A UUID is 128 bits long, and can guarantee
uniqueness across space and time. UUIDs were originally used in the
Apollo Network Computing System and later in the Open Software
Foundation's (OSF) Distributed Computing Environment (DCE), and then
in Microsoft Windows platforms.
This specification is derived from the DCE specification with the
kind permission of the OSF (now known as The Open Group).
Information from earlier versions of the DCE specification have been
incorporated into this document."
See also the gBorg "pgUUID" project:
<http://gborg.postgresql.org/project/pguuid/projdisplay.php>
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