UUID Collision Probability: Can Two UUIDs Be the Same?
The math behind UUID collision probability: birthday problem, expected collisions, and why you should not worry.
The Math
UUID v4 has 2^122 possible values (5.3 × 10^36). Using the birthday problem formula:
- Generate 1 billion UUIDs: collision probability ≈ 0.000000000000000000086%
- To reach 50% collision probability: generate 2.71 × 10^18 UUIDs
- At 1 million UUIDs/second: that takes 86,000 years
In practice, UUID collisions do not happen.
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