Which UUID version to use

Question

Which version of the UUID should you use  I saw a lot of threads explaining what each version entails  but I am having trouble figuring out what s best for what applications

User · Answer

That s a very general question  One answer is   it depends what kind of UUID you wish to generate   But a better one is this   Well  before I answer  can you tell us why you need to code up your own UUID generation algorithm instead of calling the UUID generation functionality that most modern operating systems provide    Doing that is easier and safer  and since you probably don t need to generate your own  why bother coding up an implementation  In that case  the answer becomes use whatever your O S  programming language or framework provides  For example  in Windows  there is CoCreateGuid or UuidCreate or one of the various wrappers available from the numerous frameworks in use  In Linux there is uuid generate    If you  for some reason  absolutely need to generate your own  then at least have the good sense to stay away from generating v1 and v2 UUIDs  It s tricky to get those right  Stick  instead  to v3  v4 or v5 UUIDs   Update  In a comment  you mention that you are using Python and link to this  Looking through the interface provided  the easiest option for you would be to generate a v4 UUID  that is  one created from random data  by calling uuid uuid4      If you have some data that you need to  or can  hash to generate a UUID from  then you can use either v3  which relies on MD5  or v5  which relies on SHA1   Generating a v3 or v5 UUID is simple  first pick the UUID type you want to generate  you should probably choose v5  and then pick the appropriate namespace and call the function with the data you want to use to generate the UUID from  For example  if you are hashing a URL you would use NAMESPACE URL   uuid uuid3 uuid NAMESPACE URL   https   ripple com    Please note that this UUID will be different than the v5 UUID for the same URL  which is generated like this   uuid uuid5 uuid NAMESPACE URL   https   ripple com    A nice property of v3 and v5 URLs is that they should be interoperable between implementations  In other words  if two different systems are using an implementation that complies with RFC4122  they will  or at least should  both generate the same UUID if all other things are equal  i e  generating the same version UUID  with the same namespace and the same data   This property can be very helpful in some situations  especially in content-addressible storage scenarios   but perhaps not in your particular case

User · Answer

Postgres documentation describes the differences between UUIDs  A couple of them   V3      uuid generate v3 namespace uuid  name text  - This function generates a version 3 UUID in the given namespace using the specified input name    V4      uuid generate v4 - This function generates a version 4 UUID  which is derived entirely from random numbers

User · Answer

If you want a random number  use a random number library   If you want a unique identifier with effectively 0 00   many more 0s here   001  chance of collision  you should use UUIDv1   See Nick s post for UUIDv3 and v5   UUIDv1 is NOT secure   It isn t meant to be   It is meant to be UNIQUE  not un-guessable   UUIDv1 uses the current timestamp  plus a machine identifier  plus some random-ish stuff to make a number that will never be generated by that algorithm again   This is appropriate for a transaction ID  even if everyone is doing millions of transactions s    To be honest  I don t understand why UUIDv4 exists    from reading RFC4122  it looks like that version does NOT eliminate possibility of collisions   It is just a random number generator   If that is true  than you have a very GOOD chance of two machines in the world eventually creating the same  UUID v4  quotes because there isn t a mechanism for guaranteeing U niversal U niqueness    In that situation  I don t think that algorithm belongs in a RFC describing methods for generating unique values   It would belong in a RFC about generating randomness   For a set of random numbers   chance of collision   1 -  set size     set size - tries       set size   tries

User · Answer

There are two different ways of generating a UUID   If you just need a unique ID  you want a version 1 or version 4    Version 1  This generates a unique ID based on a network card MAC address and a timer  These IDs are easy to predict  given one  I might be able to guess another one  and can be traced back to your network card  It s not recommended to create these  Version 4  These are generated from random  or pseudo-random  numbers  If you just need to generate a UUID  this is probably what you want    If you need to always generate the same UUID from a given name  you want a version 3 or version 5    Version 3  This generates a unique ID from an MD5 hash of a namespace and name  If you need backwards compatibility  with another system that generates UUIDs from names   use this  Version 5  This generates a unique ID from an SHA-1 hash of a namespace and name  This is the preferred version

[uuid] Which UUID version to use?

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