Hacking Postgres 101 — ULID function

session summary

They implemented a C prototype of a time-ordered 128-bit identifier, initially called ULID, combining microsecond time with random bytes in UUID storage. Generation speed matched gen_random_uuid(), while inserting millions of values into indexed tables remained constant instead of degrading as random UUIDs scattered writes across the B-tree. Buffer measurements showed a dramatic reduction in pages read, dirtied, and written. Rather than submit a bespoke format, they decided to align the implementation with the emerging UUIDv7 standard, which later reached core.

timecodes

1. 00:30 Why random UUIDs hurt B-tree locality
2. 05:00 Security, performance, and ordering trade-offs
3. 10:00 Preparing the in-core identifier prototype
4. 14:00 Adding the catalog function and C implementation
5. 20:00 Encoding microsecond time in network byte order
6. 31:00 First generated values and generation benchmark
7. 43:00 Comparing indexed inserts with random UUIDs
8. 48:30 Buffer evidence and decision to target UUIDv7