Question 1

What is a UUID?

Accepted Answer

A UUID (Universally Unique Identifier) is a 128-bit identifier standardized by RFC 4122. It is typically represented as 32 hexadecimal digits grouped as 8-4-4-4-12, e.g. 550e8400-e29b-41d4-a716-446655440000.

Question 2

What's the difference between UUID v1 and v4?

Accepted Answer

UUID v1 is timestamp-based and includes the MAC address of the generating machine, making it ordered but potentially revealing host information. UUID v4 is randomly generated (122 random bits), making it unpredictable and privacy-safe.

Question 3

What is a UUID v5?

Accepted Answer

UUID v5 is deterministic — it is derived from a namespace UUID and a name string using SHA-1 hashing. The same namespace and name always produce the same UUID, which is useful for generating stable identifiers from known inputs.

Question 4

What is UUID v7?

Accepted Answer

UUID v7 is a newer format (RFC 9562) that embeds a Unix millisecond timestamp in the most significant bits. This makes v7 UUIDs monotonically increasing, which is ideal for database primary keys because they sort naturally by creation time.

Question 5

Are UUIDs guaranteed to be unique?

Accepted Answer

Not mathematically guaranteed, but the collision probability is astronomically low. For UUID v4, generating 1 billion UUIDs per second for 85 years would only give a 50% chance of a single collision across the entire set.

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