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uuid 2025-02-05

UUID Versions: When to Use Which

A comprehensive comparison of UUID versions (v1, v4, v5, v7) with practical guidance on choosing the right one.

UUIDs (Universally Unique Identifiers) are 128-bit identifiers used extensively in software development. But with multiple versions available, choosing the right one matters.

UUID Format

All UUIDs follow the same format: xxxxxxxx-xxxx-Mxxx-Nxxx-xxxxxxxxxxxx where M indicates the version and N indicates the variant.

UUID Version 1: Time-based

UUID v1 uses the current timestamp and the MAC address of the machine:

f47ac10b-58cc-1bcd-8701-02c2b76aac88


                ^--- version 1

Pros:

  • Naturally sortable by creation time
  • Guaranteed unique across machines (uses MAC address)
  • Good for distributed systems without coordination

Cons:

  • Exposes the MAC address (privacy concern)
  • Exposes creation timestamp
  • Not suitable when privacy is important

UUID Version 4: Random

UUID v4 is generated entirely from random numbers:

550e8400-e29b-41d4-a716-446655440000


                ^--- version 4

Pros:

  • No information leakage
  • Simple to implement
  • Most widely used version

Cons:

  • Not sortable
  • Poor database index performance (random distribution)
  • Theoretically possible (but extremely unlikely) collisions

UUID Version 5: Name-based (SHA-1)

UUID v5 generates a deterministic UUID from a namespace and a name using SHA-1:

// Same inputs always produce the same UUID


UUID.v5('hello', UUID.DNS);  // always the same

Pros:

  • Deterministic: same input always produces same output
  • No coordination needed for the same named resource

Cons:

  • SHA-1 is no longer considered cryptographically secure
  • Not unique across different names (by design)

UUID Version 7: Time-ordered (Newest)

UUID v7 is the newest addition, combining Unix timestamp with random data:

01894130-fd29-7d57-9e81-123456789abc


^timestamp^    ^--- version 7

Pros:

  • Lexicographically sortable (great for database indexes)
  • Includes millisecond-precision timestamp
  • Better database performance than v4
  • No privacy concerns (no MAC address)

Cons:

  • Newer standard, less library support
  • Timestamp is visible (though this is often desirable)

Choosing the Right Version

Use CaseRecommended Version

|----------|-------------------|

General purpose IDsv4 Database primary keysv7 Deterministic IDs from namesv5 Time-sorted eventsv7 Legacy system compatibilityv1 Maximum privacyv4 Distributed log entriesv7

UUID in Databases

When using UUIDs as primary keys, consider:

1. v7 for sorted inserts: Reduces B-tree fragmentation

2. Binary storage: Store as BINARY(16) instead of CHAR(36) to save space

3. Indexing: v7 UUIDs perform much better than v4 for range queries

-- Using UUID v7 as primary key (MySQL)


CREATE TABLE users (


  id BINARY(16) PRIMARY KEY,


  name VARCHAR(255),


  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP


);

UUID vs Alternatives

  • Auto-increment: Simple but exposes count, not suitable for distributed systems
  • ULID: Similar to UUID v7 but uses Crockford Base32 encoding
  • CUID: Designed for horizontal scaling
  • Snowflake ID: Used by Twitter, 64-bit time-ordered ID

Generate UUIDs instantly with our UUID Generator tool.