Are UUID collisions something I should worry about?

For v4, practically no. With 122 random bits you would need to generate on the order of a billion UUIDs per second for many years before a collision becomes likely.

What is the difference between UUID and GUID?

They are the same thing. GUID is Microsoft’s name for the same 128-bit identifier standard.

Which UUID version is best for database primary keys?

UUID v7. Its time-ordered prefix keeps new rows near each other in the index, avoiding the write amplification that random v4 keys cause.

Does UUID v4 leak any information?

No. It is almost entirely random, unlike v1 which embeds a timestamp and MAC address.

UUIDs explained: v1 vs v4 vs v7, and when to use each

6 min readUpdated May 24, 2026

A UUID is a 128-bit identifier you can generate anywhere without coordination and still expect to be unique. But "UUID" is a family of versions with very different properties — picking the wrong one hurts your database.

The format

A UUID is 128 bits, shown as 32 hex digits in five dash-separated groups:

550e8400-e29b-41d4-a716-446655440000
         ^                  
         version digit

The version digit (the first character of the third group) tells you how it was generated. Generate any version in the UUID Generator.

v4 — random

Version 4 is 122 random bits. It is the default choice: no machine info leaks, and collisions are astronomically unlikely (you would need billions of UUIDs before the odds become meaningful).

Downside: randomness means new IDs scatter across a database index, hurting insert performance and locality on large tables.

v1 — time + MAC

Version 1 encodes a timestamp and the machine’s MAC address. IDs are roughly sortable by creation time, but they can leak the MAC address and creation time — a privacy concern. Rarely the right choice today.

v7 — time-ordered (the modern pick)

Version 7 puts a Unix millisecond timestamp in the high bits, followed by random bits. You get the uniqueness of v4 and roughly sortable, index-friendly IDs — ideal for database primary keys.

Use v4 for general-purpose IDs, tokens, and when ordering does not matter.
Use v7 for database primary keys where insert locality matters.
Avoid v1 unless you specifically need its legacy behavior.

Frequently asked questions

Are UUID collisions something I should worry about?: For v4, practically no. With 122 random bits you would need to generate on the order of a billion UUIDs per second for many years before a collision becomes likely.
What is the difference between UUID and GUID?: They are the same thing. GUID is Microsoft’s name for the same 128-bit identifier standard.
Which UUID version is best for database primary keys?: UUID v7. Its time-ordered prefix keeps new rows near each other in the index, avoiding the write amplification that random v4 keys cause.
Does UUID v4 leak any information?: No. It is almost entirely random, unlike v1 which embeds a timestamp and MAC address.

Try it yourself

Put this guide into practice — these tools run free in your browser.

UUID Generator Hash Generator (MD5, SHA-1, SHA-256, SHA-512)Random Number Generator