CODEWITHSUNDEEP
.netguid
Diskdrive
Diskdrive

Reputation: 18825

What are the chances of getting the same GUID in 1 billion iterations?

I am working on a project where I need to generate approximately 1 billion GUIDs.

I know GUIDs are not guaranteed to be unique but are unique almost all of the time.

If I generated a billion GUIDs, what is the probability that there will be a match?

Upvotes: 15

Views: 2747

Answers (3)

Hinek
Hinek

Reputation: 9729

Blogpost: GUIDs are globally unique, but substrings of GUIDs aren’t

The .NET GUID consists of

  • 60 bits of timestamp,
  • 48 bits of computer identifier,
  • 14 bits of uniquifier, and
  • six bits are fixed

So the UUID probability quoted by Oscar does not work here. But if you create all your 1 billion GUIDs from one computer, there is no chance to get a duplicate (except you are playing with the clock ;-)

Upvotes: 15

Robin Day
Robin Day

Reputation: 102478

If you are creating the GUIds from the same machine and using the same algorithm then you will not get a collision.

Upvotes: 5

Oscar Cabrero
Oscar Cabrero

Reputation: 4169

http://en.wikipedia.org/wiki/Uuid#Random_UUID_probability_of_duplicates

n probability

68,719,476,736 = 2^36 = 0.0000000000000004 = 4 × 10^−16)

2,199,023,255,552 = 2^41 = 0.0000000000004 = (4 × 10^−13)

70,368,744,177,664 = 2^46 = 0.0000000004 = (4 × 10^−10)

Upvotes: 2

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