UUID V4 Generator

What is UUID Version 4 (Random UUID)

UUID Version 4 (Random UUID) is the most widely used version of UUID, generated based on cryptographically strong random numbers. It is created according to Section 4.4 of the RFC 4122 standard, "Algorithms for Creating a UUID from Truly Random or Pseudo-Random Numbers."

Example: 9b1deb4d-3b7d-4bad-9bdd-2b0d7b3dcb6d

UUID Version 4 is entirely based on random or pseudo-random numbers and does not rely on timestamps or MAC addresses. This means that the generation of UUID Version 4 is completely random, with no order or pattern, making it ideal for security-sensitive applications.

Structure

UUID Version 4 adheres to the standard UUID format, which is 32 characters in the pattern 8-4-4-4-12, displayed as xxxxxxxxxxxx-xxxx-4xxx-xxxx-xxxxxxxxxxxx. Here, 'M' represents the version number, and for Version 4 UUIDs, 'M' is fixed at 4.

Application Scenarios

UUID Version 4 is suitable for scenarios where completely random unique identifiers need to be generated, such as database primary keys, temporary file names, etc. Due to its randomness, it is also very useful in distributed systems, especially when avoiding ID conflicts is required.

Features

• High Randomness: The generation of UUID Version 4 relies on a random number generator, which makes it highly random and unpredictable.
• Disorderliness: Since it does not depend on timestamps, the order of UUID Version 4 generation is unrelated to time, which helps protect privacy and reduce predictability.
• Global Uniqueness: Although there is a theoretically very small possibility of generating duplicate UUIDs, conflicts are virtually impossible in practical applications.
• Security: The randomness of UUID Version 4 makes it perform well in terms of security, being not easily predictable.

Generation Algorithm Steps

1. In the UUID structure's clock_seq_hi_and_reserved part, set the most significant bits (i.e., the 6th and 7th bits) to 0 and 1, respectively.
2. In the UUID structure's time_hi_and_version field, set the most significant four bits (i.e., bits 12 to 15) to the 4-bit version number 0100.
3. Set all other bits, except those already set, to values randomly (or pseudo-randomly) selected.

During the generation process of UUID Version 4, specific bits in certain fields are first fixed to indicate the version and clock sequence characteristics, and then all other bits are filled with values through a random or pseudo-random process. This ensures that the generated UUID has global uniqueness and strong randomness.

When to Use UUID v4

UUID Version 4 is perfect for:

• ✅ Session IDs - Web application session management
• ✅ API Keys - Temporary or permanent API authentication tokens
• ✅ Database Primary Keys - When order doesn't matter
• ✅ File Names - Temporary files, uploads, or caches
• ✅ Request IDs - Tracking requests across microservices
• ✅ Object Storage Keys - S3, Azure Blob, or similar services
• ✅ Message IDs - Queue systems like RabbitMQ or Kafka

Collision Probability

The probability of UUID v4 collision is extremely low:

• 1 billion UUIDs: 1 in 2.71 quintillion chance of collision
• 1 trillion UUIDs: 1 in 2.71 million chance of collision

In practical terms, you'll never experience a collision in production unless you're generating trillions of UUIDs.

Performance Considerations

Advantages:

• Fast generation (no I/O or network calls required)
• Can be generated in parallel across distributed systems
• No coordination between systems needed

Trade-offs:

• Not sortable by creation time
• May impact database index performance at very large scales
• Takes more storage than sequential IDs (16 bytes vs 4-8 bytes)

Tip: For database primary keys with billions of rows, consider UUID v7 for better indexing performance while maintaining uniqueness.