¿Cuáles son las posibilidades de que dos GUID colisionen?

What are the chances of two GUID collision?

So essentially the answer is yes, collisions are possible. But they are highly unlikely. The chances of two random GUIDs colliding (~1 in 10^38) is lower than the chance of not detecting a corrupt TCP/IP packet (~1 in 10^10).

UUIDs are handy for giving entities their own special names, for example, in a database. There are several ways to generate them, including methods based on time, MAC addresses, hashes, and random numbers, but they make the same promise: no two are identical. Each one is unique across space and time.

Assuming a perfect source of entropy on each device generating random GUIDs, there is a 50% chance of collision after 2.7e18 random GUIDs have been generated. That’s more than 2.7 million million million. That’s a lot. Random GUIDs cannot ever collide with other types of RFC 4122 GUIDs (e.g., time-based GUIDs).

UUIDs are commonly used as primary keys in a database – in that case, it would just fail to create the duplicate row, which may result in a minor glitch such as a session timing out immediately or something equally innocuous.

Version 4 is the random number UUID. There’s six fixed bits and the rest of the UUID is 122-bits of randomness. See Wikipedia or other analysis that describe how very unlikely a duplicate is.

Simple proof that GUID is not unique. In MSDN you can read: The chance that the value of the new Guid will be all zeros or equal to any other Guid is very low. What are the chances to get a Guid.NewGuid () duplicate?, approximations that might be useful.)

This posting is provided “AS IS” with no warranties, and confers no rights. The GUID genaration is dependant timestam there is very less possibility of Guid duplication. like if you restarted the machine and reset the system time to back in that case it may genarate duplicate guid.

If you randomly generate 2, the chance of them being the same is incredibly small. But what if you generate 1,000,000, what are the chances there is 1 or more duplicates in those 1,000,000? What about 10,000,000, or 100,000,000 or even 1 billion? Each new GUID has a chance to match all those previously inserted into the set. Graphs!

Apparently, Guid.NewGuid () generates duplicate Guids after rebooting the device. We could reproduce the problem with the following sample program, which simply generates one Guid, writes it to a database and reboots the device (Column [Id] of table [Data] is of type uniqueidentifier, DeviceHelper is a helper class simply rebooting the device).

As the number of GUIDs approach infinity, the probability for duplicate GUIDs approach 100%. In very rough terms, the square root of the size of the pool is a rough approximation of when you can expect a 50% chance of a duplicate.

Generating GUID Trivia: “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.”

GUIDs are designed for uniqueness, not for security. Even if you use one of the other GUID generation algorithms, that doesn’t solve the problem, because the purpose of a GUID is to be globally unique, not to be unguessable.

Theoretically, no, they are not unique. It’s possible to generate an identical guid over and over. From there (via Wikipedia), the odds of generating a duplicate GUID: 1 in 2^128.

6 Answers. The chances of getting two identical guids are astronomically slim even if you are generating guids as fast as you can. (Generating, say, thousands of guids per second for the sole purpose of finding a duplicate.)

GUIDs are guaranteed to be unique and that’s about it. Not guaranteed to be be random or difficult to guess.

GUIDs are globally unique identifiers, and given their rather incomprehensible presentation, some people may be tempted to use them (or parts of them) as passwords. GUIDs are designed for uniqueness, not for security.

A GUID is a 128-bit value consisting of one group of 8 hexadecimal digits, followed by three groups of 4 hexadecimal digits each, followed by one group of 12 hexadecimal digits. The following example GUID shows the groupings of hexadecimal digits in a GUID: 6B29FC40-CA47-1067-B31D-00DD010662DA.

There’s one giant caveat for GUIDs: collisions are still possible. First, the birthday paradox shows us the chance of a collision as GUIDs are used. It’s very, very unlikely that GUIDs will collide, but as more are assigned, there are fewer left to choose from.

All algorithms are designed in a way that won’t generate the same GUID twice, but here is another question — are GUIDs are 100% unique?. The answer is no, there is no guarantee of uniqueness, but there is a rare and very small chance of the same GUID being generated twice in the next fifty billion trillion years.

The problem with counting is that we want to create ID numbers without the management headache. GUIDs are large, enormous numbers that are nearly guaranteed to be unique. They are usually 128 bits long and look like this in hexadecimal: The format is a well-defined sequence of 32 hex digits grouped into chunks of 8-4-4-4-12.

Content-based (MD5 or SHA-1 hash of data): Create a GUID based on a hash of the file contents. Files with the same contents will get the same GUID. You can also seed the hash with a unique namespace (like your URL).