64位随机ID是否足以容纳大约1000万个条目？(Is a 64 bit random ID good enough for about 10 million entries?)

64位随机ID是否足以容纳大约1000万个条目？(Is a 64 bit random ID good enough for about 10 million entries?)

我受到这个唯一id代码的启发，生成一个随机的64位标识符。

我的问题：这对于大约1000万条记录是否足够好？

def self.generateId (0..15).collect{(rand*16).to_i.to_s(16)}.join end

I was inspired by this unique id code to generate a random 64 bit identifier.

My question: will this be good enough for about 10 million entries?

def self.generateId (0..15).collect{(rand*16).to_i.to_s(16)}.join end

最满意答案

这是经典的生日问题。

m=10^7且n=10^20 （自2^64 ~ 10^20 ），碰撞概率由下式给出：

p = 1 - exp(-m^2/(2*n))

给出5e-07的碰撞概率

我会说没有替换的采样是你最好的选择。

This is classic birthday problem.

With m=10^7 and n=10^20 (Since 2^64 ~ 10^20), and the collision probability is given by:

p = 1 - exp(-m^2/(2*n))

Gives a collision probability of 5e-07

I would say sampling without replacement is your best option.