At 06:57 2009-06-24, Paul McNett <[email protected]> wrote:
>Jim Dettman wrote:
> > <<The very definition of GUID is that they are guaranteed to be unique.>>
> >
> > Actually, that's not correct. There is no absolute guarantee that you
> > won't get a duplicate. But with the range on 128 bits (2^128), the chance
> > is so small that you'll get one that for all intents and purposes you can
> > assume that it is.
>
>I stand corrected.
>
>http://en.wikipedia.org/wiki/Globally_Unique_Identifier
>
>So, in the infinitesimally small chance that a dupe is generated,
>hopefully the
>database will let you know by causing a 'non unique primary key' exception.
Or someone will say that "It can never happen". When it does,
it may not be noticed but still cause a mess. Cleaning up such a
mess would not be fun.
Do not throw "infinitesimally small chance" around much. Small
probabilities can multiply. See
http://en.wikipedia.org/wiki/Birthday_paradox
Sincerely,
Gene Wirchenko
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