Re: Timestamps

[Jim Langston <jimlangston@xxxxxxxxxxxxxxxx>]

FYI,

The link again, for anyone who missed it from the midrange-l list:
http://www.ics.uci.edu/~ejw/authoring/uuid-guid/draft-leach-uuids-guids-01.txt

which describes UUIDs and how they are generated.

Regards,

Jim Langston

bvining@vnet.ibm.com wrote:
> 
> If we are talking about a UUID returned from the GENUUID MI instruction
> then there is no exposure related to getting the same value before the
> clock cycles.  The instruction has logic in it to avoid this situation.
> 
> The one exposure which does exist is that some system clocks are set
> back an hour due to Daylight Savings observation.  For systems that
> do set time back an hour then there is the possibility of timestamp
> duplication for that "repeated hour".  GENUUID attempts to miminimize
> this risk by introducing a random number into the returned UUID; but
> minimizing is not the same as eliminating.
> 
> Bruce Vining
> 
> >
> >Did you read the discussion on how a UUID is generated?  Curiously
> >enough, part of the UUID is a timestamp.  And there is discussion
> >that it is possible to have a UUID with the same value if you get
> >two values before the clock cycles.  And that you then have to
> >increment a value.  It is very interesting readying, and in OS400's
> >case those 3 zeros at the end could be incremented.
> >
> >So, basically, if you decide to generate a UUID instead of using a
> >time stamp, you are back to the exact same problem and still have to
> >find a work around.
> >
> 
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