dalroi@xxxxxxxxxxxxxxxxxxxxxxxxxxxx (Alban Hertroys) writes: >>> From wikipedia, "only after generating 1 billion UUIDs every second for >> the next 100 years, the probability of creating just one duplicate would >> be about 50%. The probability of one duplicate would be about 50% if >> every person on earth owns 600 million UUIDs." > > > Even if the chances of one person encountering a UUID collision are > about once in say 100 billion years, that could be tomorrow. It could > also not happen at all in that time span. That's how chance works. You > can never assume it won't happen. If the costs incurred by a collision > are lower than the costs of preventing it, you can choose to just take > the hit, but that doesn't go for _every_ problem domain. The medical > systems mentioned up-thread are an example of that. > > Next to that, UUID's are generated by computers. I have no doubts that > the numeric space that makes up a UUID allows for collision chances as > low as described, but are computers capable of generating those > numbers sufficiently random that they actually achieve that low a > chance? I think that's pushing it. I think I'd rather analyze this by: a) Reading the RFC, and b) Looking at some of the common implementations likely to get used rather than to merely have "a doubt." RFC 4122 does NOT point to randomness as the only criterion to discourage collisions, and treating UUIDs as if they were merely about being "sufficiently random to achieve low chance of collision" is insulting to the drafters of the standard, because they were certainly NOT so naive as to think that was sufficient. -- "cbbrowne","@","acm.org" "What I find most amusing about com and .NET is that they are trying to solve a problem I only had when programming using MS tools." -- Max M <maxm@xxxxxx> (on comp.lang.python) -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
