Hi everyone, OP here. Let me offer some background. fuuids are designed to be sortable and collision-free (for most practical purposes, details below) IDs within a 16-byte footprint making them interpretable as UUIDs.

Lazare very helpfully detailed the internals of the two available formats but I'll summarize them here and I'm happy to answer any questions:

Format A (fuuid) consists of a 4-byte second timestamp concatenated with a 12-byte random tag.

Format B (fuuid_ns) consists of an 8-byte nanosecond timestamp concatenated with an 8-byte random tag.

As far as collision resistance is concerned, here's a list of probabilities at various production rates for Format A. Collisions for Format B are only relevant when the production rate begins to approach 10^9 IDs per second (assuming IDs are produced uniformly in time).

- 2^-90.51 at 10 IDs/second

- 2^-83.73 at 100 IDs/second

- 2^-77.07 at 1,000 IDs/second

- 2^-70.42 at 10,000 IDs/second

- 2^-63.78 at 100,000 IDs/second

- 2^-57.14 at 1,000,000 IDs/second

Hope this helps!