ksuid VS ulid-mssql

OP here - we avoid sequences in all but one part of our application due to a dependency. We use [KSUIDs][1] and UUID v4 in various places. This one "gotcha" applies to any sequence, so it's worth calling out as general advice when running a migration like this.

[1]: https://segment.com/blog/a-brief-history-of-the-uuid/

UUID v4 isn't large enough to prevent collisions, that is why segment.io created https://github.com/segmentio/ksuid which is 160bit vs the 128bit of a UUIDv4.

Assuming you don't need to use UUIDv7 (or any UUID's) then https://github.com/segmentio/ksuid provides a much bigger keyspace. You could just append a string prefix if you wanted to namespace, but the chance of collisions of a KSUID is many times smaller than a UUID of any version.

KSUID's are have temporal-lexicographical order plus 128 bits of entropy, which is more than UUIDv4.

https://github.com/segmentio/ksuid

That's why you use ksuid (https://segment.com/blog/a-brief-history-of-the-uuid/) or, if you're willing to go with a draft spec you could go with the new UUID formats https://www.ietf.org/archive/id/draft-ietf-uuidrev-rfc4122bi...

Interesting in more history of UUIDs? Twilio Segment's blog has an amazing history lesson about how they came to be.

I use the ksuid from segment. https://github.com/segmentio/ksuid

Yeah, it's a small world.

I actually took the opposite path and explored several of the micro-optimized ULID libraries in C# before settling down with NUlid which I decided had the cleanest API and documentation (and reasonably good response times to GitHub issues). The implementation of Cysharp's lib has a lot of Unsafe code, which I understand why they took that path (given the focus on Unity code), but I'm hesitant about it and I liked a lot better (conceptually) how much more Span code mcb2001's CSharp.Ulid library had and if I were to micro-optimize a library that's much more the path that I would take. (But so far micro-optimizations of that sort haven't been a priority in my real world usage and I'll take the well tested library with the nice API.) I created a couple simple extension methods to do the specific "ToSqlGuid()" and "ToUlidFromSql()" that I desired for the SQL Server sort order. (Which is just shuffling the first six bytes of a ULID byte array to the end of the GUID byte array and vice versa.)

I actually trust that I can at least generate ULIDs in SQL Server, again because the part I care to be sorted/needs to be correct (the timestamp) fits into the non-endian-issue portion of a GUID in SQL Server. I've been using just the generator function from ulid-mssql [1] (I used it mostly just for DB migrations and it was nice to have for that). It was debugging the endian issues and Base-32 encoding issues of the "ULID GUID to string" functions where I gave up and decided I didn't trust doing that in database.

[1] https://github.com/rmalayter/ulid-mssql