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Re: [Qt-interest] QUuid with QUuid::Time

Subject: Re: [Qt-interest] QUuid with QUuid::Time
From: <>
Date: Tue, 15 Jun 2010 16:58:04 +0200
Constantin Makshin wrote on Monday, June 14, 2010 9:50 PM:

> IMHO, even 7 duplicates per 15 million values (~0.00005% chance of
> collision) is [more than] acceptable result for most, if not all,
> applications. :)

But can we agree upon the following: 

Given propability p1 of a "UUID collision", as suggested to be "infinitely 
small" by descriptions such as:

  "For example, consider the observable universe, which contains about 5×10^22 
stars; every star could then have 6.8×10^15 universally unique GUIDs."

and given probability p2 = ~0.00005% of a real world UUID generator 
implementation, that there are, well, "light years" (as to stay in the 
figurative speech of the 
http://en.wikipedia.org/wiki/Globally_Unique_Identifier article) between p1 and 
p2?
  
> I agree with one of the posters from that discussion:
> "chances are so low that you really should stress about something
> else- [...]"

I also generally agree on that :) It is always a question of "how bad" the 
impact of a duplicate really is and whether it is worth bothering. But for 
example if - and I stress the IF here - you'd rely on a UUID for identifying 
finanical transactions it could turn out disastrous... Or would you trust a 
bank which would officially state that "our online banking/transactions are 
(technically) 0.99995% safe"? ;)

Cheers, Oliver
-- 
Oliver Knoll
Dipl. Informatik-Ing. ETH
COMIT AG - ++41 79 520 95 22
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