UUID v4 vs UUID v7 — Which One Should You Use?

UUID v7, standardized in RFC 9562 (May 2024), addresses the main weakness of UUID v4: poor database index performance.

UUID v4 (Random)

UUID v4 uses 122 random bits and 6 fixed bits. This guarantees uniqueness without coordination but produces IDs scattered randomly across time. When used as a B-tree primary key in a database, random IDs cause page splits and index fragmentation, degrading write performance.

UUID v7 (Time-Ordered)

UUID v7 uses a 48-bit Unix millisecond timestamp followed by random bits. The timestamp prefix makes UUIDs naturally sortable by creation time, solving the B-tree fragmentation problem. Keys are still globally unique and can be generated without coordination.

Comparison

| | UUID v4 | UUID v7 | |---|---------|---------| | Standard | RFC 9562 | RFC 9562 | | Sortable | No | Yes (by time) | | DB Performance | Poor | Good | | Unique | Yes | Yes | | Leaks timestamp | No | Yes (millisecond precision) |

Recommendation: Use UUID v7 for database primary keys and UUID v4 when you explicitly do not want to reveal creation time. Try both in our UUID generator.