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?
+2
A:
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)
Oscar Cabrero
2010-06-29 06:43:38
He's talking about .NET GUIDs, they are not entirely random, like assumed in the article. There are parts caused by time and processor id(?) ... still the chance of getting a duplicate in 1 billion GUIDs is very unlikely on the same machine it may be even impossible.
Hinek
2010-06-29 06:55:33
+3
A:
If you are creating the GUIds from the same machine and using the same algorithm then you will not get a collision.
Robin Day
2010-06-29 06:58:37
+6
A:
http://blogs.msdn.com/b/oldnewthing/archive/2008/06/27/8659071.aspx
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 ;-)
Hinek
2010-06-29 07:03:54