# Sequential Unique ID Systems Comparison ## UUID/GUID - **Format**: 128-bit number (36 characters with hyphens) - **Example**: `550e8400-e29b-41d4-a716-446655440000` - **Pros**: - Globally unique across systems - No coordination needed between generators - No central authority required - Collision probability extremely low - **Cons**: - Large size (16 bytes) - Not human-readable - Not sequential by default (except UUID v1) - Poor database indexing performance ## Auto-increment integers - **Format**: Simple integer - **Example**: `1, 2, 3, 4...` - **Pros**: - Minimal storage requirements - Excellent for indexing - Human-readable - Simple to implement - **Cons**: - Reveals system information (record count) - Requires centralized sequence generator - Can cause contention in high-write systems - No built-in machine identification ## ULID (Universally Unique Lexicographically Sortable Identifier) - **Format**: 26 character string (Crockford's base32) - **Example**: `01ARZ3NDEKTSV4RRFFQ69G5FAV` - **Pros**: - Time-ordered (first 10 chars are timestamp) - Lexicographically sortable - URL-safe characters - No special characters - **Cons**: - Larger than integers (128 bits) - Less adoption than UUID - Less random than UUID (timestamp component is predictable) ## Snowflake IDs - **Format**: 64-bit integer - **Example**: `1631148800000123456` - **Pros**: - Compact (8 bytes) - Time-sortable - Distributed generation with no coordination - Includes machine identifier bits - **Cons**: - Requires careful system clock synchronization - Implementation complexity - Machine ID allocation needs management ## KSUID (K-Sortable Unique IDentifier) - **Format**: 27 character string (base62) - **Example**: `0ujtsYcgvSTl8PAuAdqWYSMnLOv` - **Pros**: - Time-sortable - Includes random component - No special characters - Reasonable size (20 bytes) - **Cons**: - Larger than integers or Snowflake IDs - Less adoption than UUIDs ## NanoID - **Format**: Configurable length, default 21 characters - **Example**: `V1StGXR8_Z5jdHi6B-myT` - **Pros**: - Customizable length and character set - URL-friendly by default - Smaller than UUID (default 21 chars) - Collision-resistant - **Cons**: - Not time-sortable - Not sequential - Not as widely adopted as UUID ## XUID (eXtended Unique IDentifier) - **Format**: Variable, often 16 characters - **Example**: `f81d4fae7dec11d0` - **Pros**: - Compact representation - Can include time component and other metadata - Flexible format for different use cases - **Cons**: - Less standardized than other formats - Implementation complexity - Varying implementations across platforms ## Selection Considerations - **Database performance**: Auto-increment and Snowflake IDs perform best - **Distribution requirements**: UUID, ULID, Snowflake, and KSUID work well in distributed systems - **Human readability needs**: Auto-increment is best, followed by encoded formats - **Security/predictability concerns**: Random UUIDs offer best security against enumeration - **Sorting by creation time**: ULID, KSUID, and Snowflake provide this naturally