Timestamps

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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