UUIDs (Universally Unique Identifiers) are 128-bit identifiers used to uniquely identify resources across distributed systems without a central authority. They are fundamental in databases, APIs, and microservices.

UUID Format

A UUID consists of 32 hexadecimal characters displayed in 5 groups separated by hyphens:

550e8400-e29b-41d4-a716-446655440000

Format: xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx

Where M indicates the version and N indicates the variant.

UUID Versions

UUID v1 — Time-based

Generated from the current timestamp and the machine's MAC address. Guarantees uniqueness but reveals the creation time and hardware identity.

Pros: Naturally sortable by time, guaranteed unique

Cons: Exposes MAC address (privacy concern), not random

UUID v4 — Random

Generated from random or pseudo-random numbers. The most commonly used version in web development.

Pros: Completely random, no information leakage, easy to generate

Cons: Not sortable, theoretically possible (but astronomically unlikely) collisions

UUID v7 — Time-ordered Random (Newest)

Combines a Unix timestamp prefix with random data. Provides the benefits of both v1 and v4 — sortable AND random.

Pros: Time-sortable, good database index performance, random suffix prevents prediction

Cons: Newer standard, not yet universally supported

UUID vs Auto-Increment IDs

When to Use UUIDs

Distributed systems with multiple databases

Merging data from different sources

Client-side ID generation (before sending to server)

When IDs shouldn't be guessable (security)

Microservices architectures

When to Use Auto-Increment

Single database applications

When sequential ordering matters

When storage size matters (4 bytes vs 16 bytes)

Simple CRUD applications

Collision Probability

For UUID v4, the probability of generating a duplicate is astronomically low. You'd need to generate about 2.71 quintillion UUIDs to have a 50% chance of a single collision. In practical terms, you could generate 1 billion UUIDs per second for 85 years before worrying.

Database Considerations

UUIDs as primary keys can cause index fragmentation with B-tree indexes

UUID v7 solves this by being time-sortable (sequential insert pattern)

Consider using BINARY(16) instead of CHAR(36) for storage efficiency in MySQL

PostgreSQL has a native uuid type that stores efficiently

Generate UUIDs instantly with our UUID Generator.

UUID Guide — Versions, Formats & When to Use Them