Question 1

What is a UUID?

Accepted Answer

UUID (Universally Unique Identifier) is a 128-bit identifier standard (RFC 4122). It's 36 characters: 32 hexadecimal digits plus 4 hyphens. Example: 550e8400-e29b-41d4-a716-446655440000. Collision probability is astronomically low - generating billions still unlikely to duplicate.

Question 2

What is the difference between UUID v1 and v4?

Accepted Answer

UUID v1 is time-based: includes timestamp (60 bits) and MAC address (48 bits). Sortable but reveals machine identity and time. UUID v4 is random: 122 random bits, no predictability or traceability. v4 recommended for privacy and security, v1 for sortable distributed IDs.

Question 3

How unique are UUIDs?

Accepted Answer

UUID collision probability is negligible. For v4: after generating 1 billion UUIDs, collision chance is 0.00000000006%. Practically guaranteed unique across all systems worldwide. No need for central coordination - generate independently and they won't clash.

Question 4

Can I use UUID as database primary key?

Accepted Answer

Yes, UUIDs are excellent primary keys for distributed systems, no central ID authority needed. Pros: globally unique, no sequential gaps, can generate client-side. Cons: larger than integers (16 bytes vs 4), slightly slower indexing, not naturally sortable (use v1 or ULID if needed).

Question 5

What is GUID vs UUID?

Accepted Answer

GUID (Globally Unique Identifier) and UUID are effectively the same. GUID is Microsoft's name, UUID is the RFC standard name. Both use same 128-bit format, same generation algorithms. Microsoft GUID = RFC UUID. Use UUID term for cross-platform, GUID for Windows-specific.

UUID Generator

UUID Structure (36 characters)

UUID Versions Reference

Developer Use Cases