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We use GUIDs extensively in our database design; Business Object properties provide Guid.Empty GUIDs for DB null values and null is always saved to the database if the value is Guid.Empty.
Apart from Guid.Empty (00000000-0000-0000-0000-000000000000) how likely is it that a GUID will be generated with all the same characters e. g.: 11111111-1111-1111-1111-111111111111
Just considering using GUIDs like these for specific values.
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Question: How many GUID combinations are there? Answer: There are 122 random bits (128 – 2 for variant – 4 for version) so this calculates to 2^122 or 5,316,911,983,139,663,491,615,228,241,121,400,000 possible combinations.
NET Core in Unix GUIDs, are generated by creating a random number of 128 bits and and doing a couple bit wise operations. In . NET Core for Windows and . NET framework it makes a remote procedure call to the Windows function UuidCreate (so it's completely up to your Windows version on how they are generated).
A GUID (globally unique identifier) is a 128-bit text string that represents an identification (ID). Organizations generate GUIDs when a unique reference number is needed to identify information on a computer or network. A GUID can be used to ID hardware, software, accounts, documents and other items.
Guid. NewGuid() initializes a new instance of the GUID class. using System; namespace GUIDTest { class MainClass { static void Main(string[] args) { System. Guid guid = System. Guid.
In short: For GUID generated according to the published standards and specifications it simply can't happen. A GUID has a structure and some of the fields actually have a meaning. What's more, .NET generates GUIDs of version 4, where it absolutely can't happen. They are defined in a way that there won't be such a GUID. For details, see below ;-)
There are five to seven bits which are the main pitfall here. Those are the version identifier (the first four bits of part three) and the variant field specifying what variant of GUID this is.
The version can be anything between 1 and 5 currently. So the only valid hex digits for which we could get such a GUID at this point are – obviously – 1 through 5.
Let's dissect the versions a little:
8, 9, A or B. This contradicts the 4 for the version number.So far we ruled out version 4 as impossible, others as highly unlikely. Lets take a look at the variant field.
The variant field specifies some bit patterns for backwards compatibility (x is a don't care), namely:
0 x x Reserved. NCS backward compatibility.
1 0 x The only pattern that currently can appear
1 1 0 Reserved, Microsoft Corporation backward compatibility
1 1 1 Reserved for future definition.
Since this pattern is at the very start of the fourth part, this means that the most significant bit is always set for the very first hex digit of the fourth part. This means that this very digit can never be 1, 2, 3 or 5. Not counting already generated GUIDs, of course. But those with the MSB set to 0 happen to be either v1 or v2. And the timestamp part of those means that they would have to be generated some millenia in the future for that to work out.
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There are exactly 5,316,911,983,139,663,491,615,228,241,121,400,000 possible combinations, so even if it wasn't designed to always be unique, the chances would be pretty remote anyway.
Source: http://msdn.microsoft.com/en-us/library/aa446557.aspx
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About as likely as any other randomly generated guids will collide. So, highly unlikely.
Though, you may want to rethink using guids to "store" data like that. They are really used to uniquely identify objects and components.
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