Are you sure that we aren't moving the goal posts here?
The OP was LESS about uniqueness and MORE about identifying NEW records. For this, wouldn't a time stamp to the micro-second be satisfactory?
-----Original Message-----
From: midrange-l-bounces@xxxxxxxxxxxx [mailto:midrange-l-bounces@xxxxxxxxxxxx] On Behalf Of Vern Hamberg
Sent: Wednesday, May 02, 2012 8:11 AM
To: Midrange Systems Technical Discussion
Subject: Re: Unique ID
Agreed - the use of a timestamp, even out to microseconds, is no longer
trustworthy as to uniqueness. And even the MI TOD value, which used to
be documented to produce a unique value - it doesn't anymore - in the
world of multiple cores. It used to report the clock ticks, which were
every 8 microsecs - at 6.1 the resolution went to 1 microsec - even so,
I've run tests that product the same value.
So this specification, well, I'm inclined to trust it until I see a
reported problem - I looked up the spec (RFC4122) and find this
interesting statement -
Since a UUID is a fixed size and contains a time field, it is possible for values to rollover (around A.D. 3400, depending on the specific algorithm used).
That should be enough for uniqueness, right? It doesn't depend on any
particular machine architecture, so far as I can tell - this RFC comes
out of the DCE work, which was a joint effort of companies like HP and
IBM and others. So the TOD issues are not part of it, so far as I know.
The algorithms are listed in the RFC, viewable at
http://www.ietf.org/rfc/rfc4122.txt
Of course, for short-term, other methods are needed - to get an object
name, UUID won't work - it's 128-bits (16 bytes) and a character
representation is 32 long.
Interesting stuff - for another day - but it can be trusted, I'm sure.
Vern
On 5/2/2012 6:19 AM, rob@xxxxxxxxx wrote:
Well, I clicked the link and I read
"The UUID is unique as an identifier across all time and space and is
consistent with the Open Systems Foundation (OSF) Distributed Computing
Environments (DCE) version 1 UUID specification described in the DCE's
"Architecture Environment Specification/Distributed Computing: for Remote
Procedure Calls", Appendix A."
Across all time and space sounds pretty darn unique to me.
Rob Berendt
midrange.com
