[developer2]

Agreed, I don't understand why anyone reaches for uuid v4; it's the dumbest thing out there that sees regular use for no reason whatsoever. The number of developers who reach for uuid v4 is scary; I swear they don't understand what it contains, or care to think critically about their use case. The worst is reading about using uuid v4 for "offline client-side ID generation", such that any client can fixate object IDs that wind up in the server's database, and in fact are likely NOT unique if you have nefarious clients purposely generating duplicates client-side.

There is also no reason to give up 6 reserved bits of a uuid v4's 128 bits (it's only 122 random bits + 6 bits of unnecessary version info). If you want random IDs, make your own. Simply generate 16 bytes of raw data; or combine two random 64-bit integers; or combine a timestamp prefix with random bytes at the end. Your needs probably don't warrant exactly 128 (well, 122 bits) that uuid v4 gives anyway, so you can customize to a specific number of bits. You can also use base62 (0-9, A-Z, a-z) or base64 instead of hexadecimal (0-9, A-F) to reduce the number of displayed characters (eg. in URLs), while omitting the stupid hyphens of a uuid too.

tldr; uuid v4 shouldn't even exist, and certainly should not be used unless integrating with pre-existing systems.

[henvic]

I'm the OP. Well, I've used UUID to generate ids on the client-side for a metrics system. Well, if someone submitted duplicated data, my server would ignore it. The context is critical to decide whether you can let clients generate an ID or not. In my case, the worst that could happen would be a Denial-of-Service attack if someone found a weakness in the UUID algorithm I relied upon.