This guaranteed uniqueness comes at the cost of anonymity. Because UUID v1 takes the time and your MAC address into consideration, this also means that someone could potentially identify the time and place i.
The generation of a v4 UUID is much simpler to comprehend. The bits that comprise a UUID v4 are generated randomly and with no inherent logic. Because of this, there is no way to identify information about the source by looking at the UUID.
However, there is now a chance that a UUID could be duplicated. The question is, do you need to worry about it? The short answer is no. If your application is mission critical for example, bank transactions or medical systems , you should still add a uniqueness constraint to avoid UUIDv4 collision. An important point to note is UUID v5 is consistent. This means that any given combination of input and namespace will result in the same UUID, every time.
You can try it out yourself:. This is great if you want to, for example, maintain a mapping of your users to their UUIDs without explicitly persisting that information to storage. For versions 3 through 5, the clock sequence sources mentioned below should be replaced with their respective sources.
The V1 UUID string is derived into an ordered sequence of 6 fields from that give the ID a great but not non-zero chance of being completely unique. UUID records are derived from the following sources, in big-endian fashion, as follows:.
For additional information around changing Node IDs and other collision considerations, see section 4. For these versions we have 74 bits of time data, 60 bits from the timestamp and 14 from the clock sequence. Along with that we have the bit Node ID, which could be the MAC or, in some cases where we may not want to expose it or the Node does not have a MAC, a 48 random or pseudo-random bits.
Ideally for the UUID version, not for us however if we have the MAC and, in combination with the timestamp and clock sequence, we are given an ID that correlates to a single point in space the node MAC and time timestamp and clock sequence.
If the ideal case holds true, a node is capable of generating 18 Sextillion , but if no MAC is given we have an additional 48 bits of uniqueness, yielding 5. According to the spec, Version 5 is preferred, since it uses SHA As with the other versions, 4 bits are used to indicate the version, and 2 or 3 bits depending on the variant are used to indicate the variant of the UUID.
Still the chances of collision are extremely small. The chance of a collision occurring where two identical UUIDS are generated at the same time on the same node is incredibly small, and the probability of collision can be calculated using the Birthday Problem.
For example , if we have 68,,, UUIDs with 74 random bits , the probability of a duplicate would be 0. If a user was generating all UUIDs for a system using a single node, they may want to consider using UUID version 4 rather than 1, since the chance of collision is much greater. About Duo. Careers Now Hiring! Product Product Explore Our Products Duo provides secure access to any application with a broad range of capabilities. Device Trust Ensure all devices meet security standards.
Adaptive Access Policies Block or grant access based on users' role, location, and more. Duo in Action Click through our instant demos to explore Duo features. Explore Demos. You need Duo. Start a Free Trial. Duo Free Free 10 users Simple identity verification with Duo Mobile for individuals or very small teams. The whole point of using UUID is that you trust it to do a better job of providing a unique ID than you yourself would be able to do.
This is the same rationale behind using a 3rd party cryptography library rather than rolling your own. Doing it yourself may be more fun, but it's typically less responsible to do so. I usually set up my DB's to have one table that contains all the keys and the modified dates and such. Haven't run into a problem of duplicate keys ever. The only drawback that it has is when you are writing some queries to find some information quickly you are doing a lot of copying and pasting of the keys.
You don't have the short easy to remember ids anymore. Funny thing is, you could generate 2 in a row that were identical, of course at mind-boggling levels of coincidence, luck and divine intervention, yet despite the unfathomable odds, it's still possible! Screenshot video! If you feel lucky, check the checkbox, it only checks the currently generated id's.
If you wish a history check, leave it unchecked. Please note, you might run out of ram at some point if you leave it unchecked. I tried to make it cpu friendly so you can abort quickly when needed, just hit the run snippet button again or leave the page. Check the checkbox if you feel lucky. For UUID4 I make it that there are approximately as many IDs as there are grains of sand in a cube-shaped box with sides ,km long.
Presumably the cloning software they used to format the drives just copied the UUID as well. Obviously UUID collisions are much more likely to happen due to a flawed cloning or copying process than from random coincidence. Bear that in mind when calculating UUID risks. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. How unique is UUID? Ask Question. Asked 12 years, 3 months ago.
Active 2 months ago. Viewed k times. Jason Jason For a large enough value of "enough time" : — lutz. If it has any potential to collide, it's not unique.
Therefore by definition, UUID is not unique, and safe only if you're prepared for potential collisions regardless of chance of collisions. Otherwise, your program is simply incorrect. You can say UUID as "almost unique" but it doesn't mean it's "unique". UUIDs are unique "for practical purposes" - the fact that there is a infinitesimally small chance of a duplicate value being generated doesn't make programs relying on this incorrect except in the very rare situation where the volume of IDs being generated starts to make that possibility statistically significant.
Show 2 more comments. Active Oldest Votes. Very safe: the annual risk of a given person being hit by a meteorite is estimated to be one chance in 17 billion, which means the probability is about 0. Caveat: However, these probabilities only hold when the UUIDs are generated using sufficient entropy. I like this part from Wikipedia: However, these probabilities only hold when the UUIDs are generated using sufficient entropy.
So what is the real chance of duplicate noting this sentence. We can not create real random numbers on computer, can we? Actually, a lot of work has gone into finding ways to introduce as much entropy "real randomness", I guess you'd call it as possible into random number APIs.
See en. That's actually a higher probability of collision than I'd imagined. Birthday paradox at, I guess. The source of entropy is typically configured at the operating system level. Show 3 more comments.
But only after using up exabytes of storage for those IDs. Is the uniqueness purely because of randomness? Or there are other factors? TheTahaan That's not what random means. It doesn't mean "totally unpredictable" -- usually they follow some kind of distribution.
It's truly random, but we absolutely can know the chance of getting a particular outcome.
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