UUID Generator

UUID v1 is created by combining the current time (100-nanosecond precision) with the generating device's MAC address. Since it contains time information, it can be sorted by creation order, and even simultaneous generation on the same device prevents collisions through clock sequence.

However, there are privacy concerns as the MAC address is exposed. Most modern implementations use random node IDs instead of actual MAC addresses, but v4 or v7 are recommended for externally exposed identifiers.

UUID v3 calculates an MD5 hash by combining a namespace UUID with a name string. It's a deterministic approach where the same namespace + same name always generates the same UUID.

Useful for converting fixed inputs like URLs or domain names to unique identifiers. However, due to MD5's security vulnerabilities, SHA-1 based v5 is recommended for new projects.

UUID v4 consists of 122 bits of pure random data and is the most widely used UUID version. Using cryptographically secure random number generators (CSPRNG), the collision probability is extremely low.

Without time information, sorting is impossible, and random insertion in database B-Tree indexes can cause performance degradation. Suitable for general unique identifiers where sorting isn't needed.

UUID v5 uses the same deterministic approach as v3 but with SHA-1 as the hash algorithm. Same namespace + same name always generates the same UUID, with higher collision resistance than MD5.

V5 is recommended over v3 when you need reproducible identifiers from fixed inputs.

UUID v7 is a new UUID version defined in RFC 9562, published in 2024. The upper 48 bits contain a Unix timestamp (milliseconds), with the rest being random data. Since the timestamp is in the upper bits, lexicographic sorting = chronological sorting.

Unlike v1, it doesn't use MAC addresses, so there are no privacy concerns. Like v4, it has randomness but sorts chronologically. When used as a database primary key, sequential insertion into B-Tree indexes significantly improves write performance compared to v4.

For new projects, v7 is the best choice for DB primary keys or sorted identifiers.