[Dylan16807]

Are you sure about that math?

A billion seconds at a billion requests per second is already 2^60 items. You'd only need a few billion seconds to have a 50:50 collision chance with 128 random bits, and even less with a real UUID that only has 122 random bits.

You'd hit 1% odds of collision after less than a decade.

If you actually want to go for a billion years, you need to expand that UUID by 50%.

[mabbo]

You know I think I converted powers of two and powers of ten interchangeably in my calculations. You're very likely correct.

[danielmarkbruce]

This seems off. A few billion seconds to have a 50:50 chance? Why wouldn't it be a billion seconds at a billion per second (2^60 total requests) would give a 1 in 2^68 chance (or 1 in 2^62 if its really only 122 bits)?

[Dylan16807]

Birthday paradox. The number of opportunities to collide is the number of items squared. (Divided by two and a smidge)

[danielmarkbruce]

Lol. I must be brain dead. Yes.

[penteract]

Because we're talking about collisions, as opposed to comparing 2^64 independent pairs. With 2^128 possible values, if you've picked 2^63 distinct ones, the chance that a randomly selected value collides with one of those is 1 in 2^65. If none of your second batch of 2^63 collide with each other, that gives a 2^63/2^65 = 1/4 chance of one of them colliding with the first batch. Considering the possibility of collisions within each batch of 2^63 brings it closer to 1 in 2.