UUID vs GUID vs ULID: Which Unique Identifier Should You Choose?

Choosing the right unique identifier format is crucial for database performance, primary keys alignment, and distributed systems scale.

UUID vs GUID

For most practical purposes, UUID (Universally Unique Identifier) and GUID (Globally Unique Identifier) are the same thing:

• UUID: Defined by RFC 4122.
• GUID: Microsoft's implementation term for UUID.

Both are 128-bit numbers formatted as 5 hex blocks separated by hyphens.

The Rise of ULID (Universally Unique Lexicographically Sortable Identifier)

A major drawback of UUID v4 is that it is entirely random. When used as database clustered index keys, random writes cause index fragmentation and slow down database inserts.

ULIDs solve this problem by incorporating a millisecond-precision timestamp at the start:

• Structure: 26 characters (Crockford's Base32 encoding, no hyphens).
• Sortable: Because it starts with a timestamp, ULIDs are sortable chronologically, making them excellent primary keys.
• Collision Resistance: Includes 80 bits of random entropy.