Comment by qbane
1 day ago
Okay, sightly more bits than UUID v4. The whole article is merely reasoning "why at least 128 bits are required", and if you smuggle some non-random data inside these bits the entropy can only drop, making it more vulnerable to collision, i.e. inferior to UUID v4.
I kind of addressed this in https://news.ycombinator.com/item?id=48060549
Actually, because the birthday paradox has k^2 as a term, this is actually less true than you might think. Having a time component actually reduces the chance of collisions over the long run, albeit at a cost of reducing the number that can be safely generated in any given quantum.
If you consider a 128-bit random number, you effectively have 64 bits of allocation space before you are likely to get a collision.
If you devote 48-bits to time, which provides millisecond accuracy for 9000 years, you then have 80 bits of randomness, effectively giving 40 bits of allocation space per millisecond before you are likely to get a collision.
Instead of approx 2^64 allocations across all time before a collision, you instead have 2^40 (1 trillion per millisecond). That sounds like a poor deal, until you realise that the factor is only 2^24, or 16777216ms or under 280 minutes.
So in reality, reducing the random space and increasing bits that are guaranteed unique is actually a great trade.
I realized that my mentioning UUID without v4 was misleading.