PostgreSQL stores UUIDs as 16-byte native types with no performance penalty. MySQL's InnoDB clustered index makes random UUID v4 fragmentation far worse than in PostgreSQL. MongoDB's ObjectId is 12 bytes with an embedded timestamp. Here's how UUID primary keys actually behave in each database and the ORM patterns to use them correctly.
Twitter, Discord, and Instagram all built custom ID systems because UUID couldn't handle time-sortability, distributed generation, and 64-bit constraints simultaneously. Here's how Snowflake IDs work, what ULID and CUID2 offer, and when each alternative makes sense.
UUID v1, v3, v4, v5, and v7 all work differently and suit different use cases. Here's when to use each — including why v7 is now the recommended choice for database primary keys.
Learn what UUIDs are, the differences between versions 1, 4, and 7, when to use UUIDs over auto-increment integers, and how to generate them instantly with a free UUID generator.
