Re: Re: 7.2 items

Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> Franck Martin <franck(at)sopac(dot)org> writes:
> > The uuidgen program creates a new universally unique identifier (UUID)
> > using the libuuid(3)
> > library. The new UUID can reasonably be considered unique among all
> > UUIDs created on the
> > local system, and among UUIDs created on other systems in the past and
> > in the future.
>
> "Reasonably considered"?
>
> In other words, this is a 64-bit random number generator. Sorry, I
> think the odds of collision would be uncomfortably high if we were to
> use such a thing for OIDs ... certainly so on installations that are
> worried about running out of 32-bit OIDs. It sounds to me like uuidgen
> is built on the assumption that only relatively small numbers of IDs
> will be demanded from it.

uuidgen with the -t option generates a UUID which includes the current
time and the Ethernet hardware address. The value is about as
globally unique as it is possible to create in 128 bits. The same
algorithm is used by DCE, and a variant is used by DCOM. To be used
properly, you need to coordinate on one machine to ensure that
different processes on that machine don't generate the same UUID.

Here is a description:
http://www.opengroup.org/onlinepubs/9629399/apdxa.htm#tagcjh_20

Ian