Re: [PATCHES] Patch for UUID datatype (beta)

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Harald Armin Massa" <haraldarminmassa(at)gmail(dot)com>
Cc: "Gevik Babakhani" <pgdev(at)xs4all(dot)nl>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: [PATCHES] Patch for UUID datatype (beta)
Date: 2006-09-18 16:15:51
Message-ID: 29546.1158596151@sss.pgh.pa.us
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"Harald Armin Massa" <haraldarminmassa(at)gmail(dot)com> writes:
> They also talk about a "guaranteed differentness" - and as much as I
> understand, they are Unique as long as the MAC-Adresses of the Network-Cards
> are unique, and fall back to "extremly likely" when there is no network card
> present.

MAC addresses are not guaranteed unique (heck, on Apple machines they're
user-assignable, and I think you can change 'em on Linux too). Another
unrelated-to-reality assumption in the above claim is that the local
system clock is always accurate (is never, say, set backwards).

You can have a reasonably strong probability that UUIDs generated per spec
within a single well-run network are unique, but that's about as far as
I'd care to believe it.

regards, tom lane

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