Question 1

What is a UUID?

Accepted Answer

A UUID (Universally Unique Identifier) is a 128-bit label used to uniquely identify information in computer systems. It is formatted as 32 hexadecimal digits split into five groups by hyphens (e.g., 550e8400-e29b-41d4-a716-446655440000). UUIDs are standardized by RFC 4122 and are used in databases, software, and distributed systems.

Question 2

What is the difference between UUID and GUID?

Accepted Answer

UUID and GUID refer to the same concept. UUID (Universally Unique Identifier) is the open standard term defined by RFC 4122. GUID (Globally Unique Identifier) is Microsoft's implementation of the same standard. They are interchangeable and have the same format.

Question 3

What is UUID version 4?

Accepted Answer

UUID v4 is the most commonly used UUID variant. It is generated using random or pseudo-random numbers, making it statistically unique without requiring a centralized registry or network access. The 13th digit is always '4' and the 17th digit is '8', '9', 'a', or 'b' to indicate the variant.

Question 4

Are UUIDs truly unique?

Accepted Answer

UUIDs are not mathematically guaranteed to be unique, but the probability of a collision is astronomically small. UUID v4 has 122 bits of randomness, meaning you would need to generate approximately 2.7 quintillion UUIDs before having a 50% chance of a single collision. For all practical purposes, UUIDs can be treated as unique.

Question 5

When should I use a UUID vs an auto-increment ID?

Accepted Answer

Use UUIDs when you need IDs that are globally unique across multiple systems, databases, or services — common in distributed architectures and microservices. Use auto-increment IDs when you need simplicity, smaller storage footprint, and sequential ordering within a single database. UUIDs are harder to guess (better for security) but larger and slower to index than integers.

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