alt Hacker NewsUnder what circumstances is it prone to conflicts? On separate threads/hosts/processes, id's created within the same millisecond would be differentiated by the 80 bits of randomness (more than UUID v7).
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sedatk • last Tuesday at 11:39 PM
See my sibling comment.
No, ULID has a "monotonic" feature, where if it detects the same millisecond timestamp in back to back calls, it just increments the 80 bit "random" portion. This means it has convoying behavior. If two machines are generating ids independently and happen to choose initial random positions near each other, the probability of collision is much higher than the basic birthday bound.
I think this "sort of monotonic but not really" is the worst of both to be honest. It tempts you to treat it like an invariant when it isn't.
If you want monotonicity with independent generation, just use a composite key that's a lamport clock and a random nonce. Or if you want to be even more snazzy use Hybrid Logical Clocks or similar.