Quick recommendation: For the safest, standards-based choice, use
GUID / UUID v4 (fully random) or
GUID / UUID v7 (time-ordered for databases). Consider
KSUID only when you need its specific 160-bit size, second-precision timestamps or your ecosystem already supports it.
K-Sortable Unique Identifier (KSUID) - github.com
Overview
KSUID (K-Sortable Unique Identifier) is a 160-bit time-ordered identifier created by Segment. Unlike standard GUIDs / UUIDs (128 bits), KSUID uses a larger ID space and second-precision timestamps (rather than millisecond), making it suitable for high-volume logging and event tracking systems.
When choosing an identifier for your application or database schema, you're usually deciding between standard GUIDs / UUIDs (governed by RFC 9562) and KSUID, a non-standard format with specific trade-offs for large-scale systems.
Comparison table
| Property | GUID / UUID v4 | GUID / UUID v7 | KSUID |
|---|
| Size | 128-bit | 128-bit | 160-bit |
|---|
| Encoding | Hex (8-4-4-4-12) | Hex (8-4-4-4-12) | Base62 (27 chars) |
|---|
| Time-sortable | No | Yes (millisecond) | Yes (second) |
|---|
| Standard | RFC 4122 and RFC 9562 | RFC 4122 and RFC 9562 | No RFC |
|---|
| Human-readable | Moderate
Hex with hyphens | Moderate
Hex with hyphens | Good
Base62, compact |
|---|
| Database-friendly | Good
Native UUID support, but random | Excellent
Native support + sortable | Moderate
Larger storage |
|---|
| Collision resistant | Excellent
122 bits random | Excellent
74 bits random | Excellent
128 bits random |
|---|
| Best for | General-purpose IDs, privacy-friendly identifiers (no embedded data) and fully random | Database primary keys, event ordering, time-correlated IDs with millisecond precision | Large-scale logging, event tracking systems requiring second-precision and 160-bit space |
|---|
Detailed comparison
Structure: 128 bits with 122 bits of randomness. No timestamp information.
- Pros: Universally supported, RFC standard, no time leakage and simple generation
- Cons: Random insertion pattern can cause index fragmentation in some databases
- Use when: You want maximum compatibility and don't need time-ordering
Example: 550e8400-e29b-41d4-a716-446655440000
Structure: 128 bits with 48-bit Unix millisecond timestamp prefix + 74 bits randomness.
- Pros: RFC standard, time-ordered, database-friendly and widely supported
- Cons: Reveals creation timestamp (millisecond precision)
- Use when: You want time-ordering with RFC compliance for database primary keys
Example: 018f3f5e-1c2d-7a9b-8f10-3c4d5e6f7a8b
KSUID (K-Sortable Unique Identifier)
Structure: 160 bits with 32-bit Unix second timestamp + 128 bits randomness, encoded in Base62.
- Pros: Larger ID space (160 bits), time-ordered, URL-safe Base62 encoding and second-precision timestamps
- Cons: Not RFC standard, requires library support, larger storage than GUIDs / UUIDs and less universal
- Use when: You need high-volume event tracking with second-precision and your stack supports KSUID
Example: 0ujsszwN8NRY24YaXiTIE2VWDTS
Which one should you use?
- Choose GUID / UUID v4 if you want the safest default: widely supported, easy to store, no embedded metadata and simple generation.
- Choose GUID / UUID v7 if you want a standards-based ID that is time-ordered with millisecond precision and typically behaves better as a database primary key than random GUIDs / UUIDs.
- Choose KSUID if you need a larger ID space (160 bits) for very high-volume systems, second-precision timestamps and your infrastructure already supports it.
Practical guidance for databases
If your main concern is database performance and index locality, you usually want identifiers that don't insert randomly across the index. That's the most common reason developers compare GUID / UUID v7 and KSUID.
- Most compatible: GUID / UUID v4 (works everywhere, but can be random for indexes)
- Best "standard + sortable" combo: GUID / UUID v7 (time-ordered with millisecond precision while staying a real GUID / UUID)
- Non-standard but larger space: KSUID (sortable with second precision, but 160 bits and may require extra tooling)
Performance considerations
- B-tree indexes: Time-ordered IDs (v7, KSUID) reduce page splits and improve insert performance in databases using B-tree indexes (PostgreSQL, MySQL, etc.).
- LSM-tree databases: Random IDs (v4) may perform better in some LSM-tree databases (Cassandra, ScyllaDB), but this depends on partitioning strategy.
- Storage overhead: UUIDs are 128 bits (16 bytes), KSUIDs are 160 bits (20 bytes) - consider the storage difference at scale.
Interoperability and ecosystem support
GUID / UUID has the broadest support across programming languages, databases, and frameworks:
- Databases: Native GUID / UUID types in PostgreSQL, MySQL, SQL Server, Oracle, etc.
- Languages: Built-in support in Java, C#, Python, Go, Ruby, JavaScript, and many more
- APIs: JSON, REST, GraphQL commonly use GUID / UUID for resource identifiers
- ORMs: Entity Framework, Hibernate, Django ORM, and many others natively handle GUIDs / UUIDs
KSUID requires library support and custom handling in many systems:
- Must be stored as strings or binary blobs in databases (no native KSUID types)
- Requires third-party libraries for generation and parsing
- May need custom converters for ORMs and serialization frameworks
- Limited language support compared to GUIDs / UUIDs
Other identifier formats
Beyond GUIDs / UUIDs and KSUID, there are many other identifier formats each with their own trade-offs. For a comprehensive comparison of all popular identifier formats, see our complete identifier comparison guide.
For most applications requiring broad compatibility and standards compliance, standard GUIDs / UUIDs remain the recommended choice.
Warnings and trade-offs
- Identifiers are not secrets: GUID / UUID v4 / v7 and KSUID are identifiers, not security tokens. Do not use them as access tokens or authentication secrets.
- Sorting depends on representation: "time-sortable" usually means the string form sorts by time, but database storage/byte-order can change behavior (varies by database/driver).
- Non-standard formats: KSUID is not an RFC UUID. Some APIs, ORMs, and databases assume GUID / UUID formatting and won't accept it without custom handling.
- Time leakage: time-ordered IDs can reveal approximate creation time. If that matters, prefer GUID / UUID v4 or treat IDs as private/internal.
- Interoperability matters: if you work across many systems or languages, GUIDs / UUIDs typically win due to universal support.
- Migration complexity: switching from one identifier format to another in an existing system can be challenging and may require data migration.
- Storage size: KSUID is 25% larger than UUID (160 bits vs 128 bits), which can add up in large-scale systems.
Frequently Asked Questions
No. KSUID is a GUID/UUID-like identifier but is
160 bits instead of 128 bits, uses Base62 encoding instead of hex, and has second-precision timestamps. It's not governed by
RFC 9562. If you need a standards-based GUID / UUID, prefer
v4 or
v7.
KSUID uses a 32-bit timestamp (seconds since epoch) + 128 bits of randomness, totaling 160 bits. This design provides a very large ID space while maintaining second-precision time ordering. The larger size trades storage efficiency for additional entropy and longer timestamp validity (until year 2106).
A common modern choice is
GUID / UUID v7 because it remains a real GUID / UUID while offering time-ordered behavior with millisecond precision, which reduces index fragmentation in B-tree databases.
GUID / UUID v4 is the simplest universal option. KSUID offers similar benefits to v7 but sacrifices
RFC compliance and uses more storage (160 bits vs 128 bits).
No. GUID / UUID is 128 bits while KSUID is 160 bits, and their internal structures differ significantly (different timestamp encodings, different bit layouts). You cannot meaningfully convert one format to another without losing information. Choose one format and stick with it for consistency.
KSUID is generally considered more human-readable due to Base62 encoding (no special characters, alphanumeric only). Example: 0ujsszwN8NRY24YaXiTIE2VWDTS. GUIDs / UUIDs use hex with hyphens: 550e8400-e29b-41d4-a716-446655440000. For most purposes, GUIDs / UUIDs are "readable enough" and offer better ecosystem support.
Extremely low. KSUID has 128 bits of randomness per second, providing significant entropy to make collisions negligible in practical scenarios. However, ensure your random number generator is cryptographically secure. Poor implementations can increase collision risk.
No. Since KSUID is 160 bits and PostgreSQL's
uuid type is 128 bits, they're incompatible. You must store KSUID as
text (27 characters) or
bytea (20 bytes) in PostgreSQL. For native PostgreSQL support and broad compatibility, use standard
GUIDs / UUIDs.
Both
GUID / UUID v7 and
KSUID are excellent for logging and event tracking. v7 provides millisecond-precision timestamps with
RFC compliance, while KSUID offers second-precision with a larger ID space. Choose v7 for broader compatibility, KSUID if you specifically need its properties and have library support.
Choose
KSUID when you need: (1) a larger ID space (160 bits) for ultra-high-volume systems, (2) second-precision is sufficient (millisecond precision not needed), (3) Base62 encoding is preferred, or (4) your infrastructure already uses KSUID. Otherwise,
GUID / UUID v7 is typically a better choice due to RFC compliance and broader ecosystem support.
Conclusion
For broad interoperability and standards compliance, choose a standard GUID / UUID: v4 for general-purpose fully random IDs or v7 for time-ordered database-friendly identifiers with millisecond precision.
Choose KSUID when your ecosystem already uses it, when you need its specific 160-bit size and second-precision timestamps, or when its operational trade-offs (larger storage, Base62 encoding) are a deliberate fit for your system. However, be aware of the interoperability costs and library support requirements.