I'm building an object database. In different places, it uses four different categories of IDs, depending on requirements: 1. Compact sequential is used, obvio

I'm building an object database. In different places, it uses four different categories of IDs, depending on requirements: 1. Compact sequential is used, obviously, where order matters. It has the drawback of requiring a coordination with a singleton. (This can be sharded/vectorized, of course.) Aside from that, it also leaks the number of objects/transactions, just by looking for the highest number available. Can be varint-encoded very nicely. 2. Compact non-sequential is used where I need a small identifier, but not leak the number of objects. Since it's compact, I must still guarantee uniqueness as in (1). This is currently implemented using a block cipher on top of the compact sequential ID generator. The drawback of this is that the domain may still be in guessable territory, depending on how much is generated. A 64-bit integer filled with 4B only requires 4B guesses to hit a collision. I don't use this much. The key can never be rotated: a key number would eat up precious bits. 3. Sparse random, used where non-guessability is important, aside from not leaking rates/counts. Take a Google Docs sharable link as an example. I doubt YouTube cares about this. This is where something like a 128-bit number like UUID or ULID shines. The space is large enough that uniqueness is assumed, given a decent PRNG. Sure, I try to use the nicest one at any given point (e.g. using a compact sequential instead of non-sequential during debugging.) But fact is that sparse random just tick more boxes. 4) Sparse, human readable. For "vouchers". They are bearer tokens that give requests more powers, e.g. to create an account or act as admin. These should be reasonably human readable, so they can be spoken. They obviously need to be sparse and hard to guess, which requires a trade-off in length. I present them in three ways: base32, english words and QR-code. Pick one; they all do the same. For copy-pasting, base32 might be best (or base58, by all means.) For shouting to a colleague, the sequence of english words might be better. I'd add other languages as needed: it's just a fixed list of words. The nice thing is it can encode the sequence in base-500 or base-1000 without being obnoxious. (The Matrix protocol and others use emoji lists, but it's the same idea. [1]) Finally, if you have a phone in your pocket or camera on your computer, perhaps the QR-code is the easiest way to use the voucher code. [1] Actually, IIRC, Matrix only uses 64 emojis, which feels a bit wasteful.