On 03 May 2012 00:38, Richard Wilson wrote:
As for "The UUID is unique as an identifier across all time and
space" In a site with more than 1 box I'd trust that about as far as
I could throw a politician

While I would consider the quote within the above quoted message to be hyperbole, in consideration of a "site with more than 1 box" the uniqueness is established additionally within a component of the UUID which should, according to /networking/ concepts [which already necessitates further uniquely identify each "box"], similarly extend the uniqueness to each "box".

A more appropriate claim might be either of "A UUID is 128 bits long, and *can* guarantee uniqueness across space and time" from http://www.ietf.org/rfc/rfc4122.txt or "is either guaranteed to be different from all other UUIDs/GUIDs generated until 3400 A.D. or extremely likely to be different (depending on the mechanism chosen)" from http://www.opengroup.org/dce/info/draft-leach-uuids-guids-01.txt

A quick web search found the above links, and the following links. The following link may be an appropriate description; see "The node ID":
http://www.famkruithof.net/guid-uuid-timebased.html
"... The node ID should <ed: preferably be> an IEEE 802 MAC address ... If no IEEE 802 address is available one can also generate a random part for this address, in this case the multicast bit (least significant bit of the first byte) must be set to 1, this to avoid clashes with legitimate IEEE 802 addresses. In case a random address is used, uniqueness cannot be guaranteed."

Corroborated at least somewhat by:
http://searchsoa.techtarget.com/definition/UUID
"A UUID (Universal Unique Identifier) is a 128-bit number used to uniquely identify some object or entity on the Internet. Depending on the specific mechanisms used, a UUID is either guaranteed to be different or is, at least, extremely likely to be different from any other UUID generated until 3400 A.D. The UUID relies upon a combination of components to ensure uniqueness. A guaranteed UUID contains a reference to the network address of the host that generated the UUID, a timestamp (a record of the precise time of a transaction), and a randomly generated component. Because the network address identifies a unique computer, and the timestamp is unique for each UUID generated from a particular host, those two components should sufficiently ensure uniqueness. However, the randomly generated element of the UUID is added as a protection against any unforeseeable problem. ..."

And of course from the expected domain, where Version 1 concurs, but mention of up to a Version 5:
http://en.wikipedia.org/wiki/Universally_unique_identifier
" ...
Version 1 (MAC address)

Conceptually, the original (version 1) generation scheme for UUIDs was to concatenate the UUID version with the MAC address of the computer that is generating the UUID ...

Version 5 (SHA-1 hash)

Version 5 UUIDs use a scheme with SHA-1 hashing; otherwise it is the same idea as in version 3. RFC 4122 states that version 5 is preferred over version 3 name based UUIDs, as MD5's security has been compromised. ...
"

Regards, Chuck

This thread ...


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