Sequential integer IDs work perfectly until you have multiple databases, multiple data centres, or multiple microservices generating records simultaneously. UUID solves the coordination problem that sequential IDs cannot — at a performance cost that is worth understanding before committing to the approach.
The Coordination Problem
Sequential integer auto-increment IDs require a single authoritative source to assign the next ID. In a distributed system with multiple write nodes, this creates a bottleneck: every insert must coordinate with a central sequencer, or nodes must use ID ranges allocated ahead of time. UUIDs eliminate this entirely — any node can generate a globally unique ID independently.
UUID Versions: Which One to Use
UUID v1 uses a timestamp and the host machine's MAC address. The embedded MAC address is a privacy concern. UUID v4 uses pure random numbers — the version used by this tool. UUID v6 and v7 are recent standards that restore time-ordering (v7 uses Unix milliseconds as the prefix) while preserving global uniqueness. UUID v7 is increasingly recommended for database primary keys because it sorts chronologically, improving B-tree index performance.
Generate UUID v4 identifiers in bulk with the UltraToolkit UUID Generator. Generate up to 100 UUIDs at once — useful for seeding databases, test fixtures, and batch record creation.
The Performance Trade-off
UUID primary keys in traditional B-tree indexes (used by PostgreSQL, MySQL, and most SQL databases) cause index fragmentation because random UUIDs insert in random positions rather than always appending to the end. This degrades insert performance at scale. UUID v7 solves this by making UUIDs time-ordered, so new records mostly append to the end of the index.
UUID Collision Probability
UUID v4 has 122 bits of randomness. To have a 50% probability of a collision, you would need to generate 2.71 quintillion UUIDs — approximately 86 years of generating one billion UUIDs per second. In practice, UUID collisions essentially never happen. The risk is not worth engineering around in any real application.