Choosing The Right UUID Version: v1, v4, v6, Or v7

Unique identifiers are a fundamental part of every software system. Every record in a database, every user account, every transaction or event relies on them to exist, be referenced, and move reliably across systems.

For small or simple applications, sequential IDs might suffice, but as systems grow, become distributed, or need to scale globally, these traditional identifiers quickly reach their limits.

Modern software architectures demand identifiers that are globally unique, independently generatable, and ideally time-sortable to support database performance and operational observability. UUIDs, or Universally Unique Identifiers, are a widely used standard, but not all UUID versions are created equal.

Selecting the right version, whether v1, v4, v6, or v7, can have long-term implications on database efficiency, operational complexity, and even security.

In this article, we'll walk through the different UUID versions, explain their structure and behavior, and provide guidance on choosing the right UUID for your system.

Why Choosing the Right UUID Version Matters

Identifiers aren't just arbitrary labels, they shape how your system performs and scales. In distributed systems, the version of UUID you use can influence several critical aspects:

• Database performance: Random identifiers can fragment indexes and reduce write throughput, while time-ordered IDs keep inserts mostly sequential.
• Operational complexity: Some UUID versions require careful clock management or node coordination.
• Security and privacy: Certain UUIDs expose timestamps or node identifiers.
• Observability: Time-ordered IDs make it easier to reconstruct the order of events without relying on additional metadata.

Getting the UUID version right early in the design process can save teams from headaches later, particularly as data volume and system complexity grow.

An Overview of UUID Versions

Before diving into details, here's a snapshot of the four most commonly discussed UUID versions:

Each version balances uniqueness, ordering, privacy, and operational simplicity differently. The right choice depends on the specific requirements of your system and the trade-offs you're willing to make.

UUIDv1: Classic Time-Based Identifiers

UUIDv1 was the original time-based UUID standard. It combines a timestamp with a node identifier, typically a MAC address, to ensure global uniqueness. While older, it can still be useful in certain internal or legacy systems.

Structure of UUIDv1:

• Timestamp: 60 bits representing 100-nanosecond intervals since October 15, 1582.
• Node ID: 48 bits, often the machine's MAC address.
• Clock sequence: 14 bits to prevent collisions when the clock goes backward.

Example:

f47ac10b-58cc-11e4-8c21-0800200c9a66

UUIDv1 includes timing information and node details, which can be useful for internal systems but raises privacy concerns for public-facing applications.

When to use UUIDv1:

• Legacy systems that already rely on time-based UUIDs.
• Internal enterprise applications where privacy is not a concern.
• Transitional systems planning to migrate to newer UUID standards like v6 or v7.

UUIDv4: Fully Random Identifiers

UUIDv4 is the most widely used UUID version for modern applications that prioritize privacy. Unlike v1, it contains no time or hardware information—its uniqueness comes entirely from randomness.

Structure:

• 122 bits of random data.
• Version and variant bits for UUID compliance.

Example:

550e8400-e29b-41d4-a716-446655440000

UUIDv4 is simple to generate, widely supported, and safe for public exposure. The downside is that it is not time-ordered. In high-throughput databases, random UUIDs can fragment indexes and reduce cache efficiency.

When to use UUIDv4:

• Public APIs or client-facing systems where privacy is critical.
• Medium-scale systems where database index fragmentation is not a concern.
• Applications that don't need chronological ordering of records.

UUIDv6: Reordered Time-Based Identifiers

UUIDv6 is a modern twist on UUIDv1. It reorders the timestamp to the beginning of the identifier, which improves sequential ordering in databases while remaining compatible with the UUID ecosystem.

Structure:

• Timestamp: 60 bits, reordered to the start.
• Node ID: 48 bits.
• Clock sequence: Ensures uniqueness.

Example:

1eb21c7e-1b9b-6c41-95d3-0c9a66f47ac1

By prioritizing the timestamp at the beginning, UUIDv6 reduces database index fragmentation and supports better insert performance. It still exposes the timestamp and potentially node information, so privacy concerns remain.

When to use UUIDv6:

• Databases that benefit from sequential inserts.
• Systems transitioning from UUIDv1 to a more efficient ordering.
• Applications that need partial chronological ordering while staying compatible with existing UUID tools.

UUIDv7: Modern Time-Sortable Identifiers

UUIDv7 is designed specifically for modern distributed systems. It uses a Unix timestamp in milliseconds combined with random bits for uniqueness. Unlike v1 or v6, it does not expose MAC addresses, making it safer for public-facing systems while still supporting sequential inserts.

Structure:

• Timestamp: 48 bits representing milliseconds since the Unix epoch.
• Random data: 74 bits to ensure uniqueness.
• Version/variant bits: Indicate UUID compliance.

Example:

018f3c2b-7c5a-7b91-9c8e-2f1c4d3a9b12

UUIDv7 is fully time-sortable, compatible with existing UUID libraries, and easy to generate independently across services. It combines the best aspects of ordering, privacy, and operational simplicity.

For teams adopting UUIDv7, Authgear's UUIDv7 tool is a practical option. It allows developers to generate compliant identifiers, inspect embedded timestamps, and verify UUID structure, helping integrate time-sortable UUIDs seamlessly into distributed systems.

When to use UUIDv7:

• High-throughput distributed databases.
• Logs, audit trails, and event stores that benefit from chronological ordering.
• Systems replacing older UUID versions for modern architectures.

Comparing the Versions

Each UUID version prioritizes different system characteristics. Here's a practical comparison:

From a database perspective, UUIDv7 often strikes the best balance for modern distributed systems.

Database Considerations

How identifiers interact with databases can have a significant impact on performance:

• Random UUIDs (v4): Can fragment indexes, increase page splits, and reduce cache efficiency.
• Time-based UUIDs (v1, v6, v7): Keep inserts mostly sequential, improving cache locality and write performance.
• Binary vs string storage: Storing UUIDs as 16-byte binary values is more efficient than using 36-character strings.

For distributed or write-heavy systems, UUIDv7 generally provides the best performance and scalability.

When implementing authentication systems with time-sortable identifiers, understanding session vs token authentication tradeoffs is essential for choosing the right architecture.

Security and Privacy Considerations

Different UUID versions expose different levels of information:

• v1 and v6: Include timestamps and node identifiers, potentially revealing system details.
• v4: Fully random, minimal exposure.
• v7: Only exposes a timestamp, generally safe for public-facing systems.

When using UUIDs in URLs, APIs, or logs, it's important to consider privacy and threat models.

For a comprehensive overview of authentication security patterns, see our guide on session management best practices.

Operational Guidance

Selecting the right UUID version also involves considering operational complexity. Here's how different versions fit:

• New distributed systems: UUIDv7 is typically the safest choice, balancing sequential ordering, privacy, and ease of generation.
• Privacy-sensitive applications: UUIDv4 is preferred when exposure of creation time or system details is a concern.
• Legacy systems: UUIDv1 may still be used internally, with an eye toward migration to v6 or v7.
• High-throughput numeric systems: Snowflake-style integer IDs may still be relevant for applications requiring compact numeric IDs.

Other practical tips include:

• Store UUIDs in binary form wherever possible for efficiency.
• Document your UUID generation strategy to prevent inconsistencies across services.
• Avoid exposing internal node or system details unless necessary.

Making the Right Choice

There is no one-size-fits-all UUID version. The ideal choice depends on system scale, database behavior, operational maturity, and privacy requirements. Some practical recommendations:

• Default to UUIDv7 for most modern distributed systems.
• Use UUIDv4 when privacy is critical and ordering isn't needed.
• Avoid UUIDv1 in public-facing contexts.
• Consider operational constraints like clock drift when using v1 or v6.
• Evaluate database behavior, sequential inserts are far easier to manage than random ones.

By approaching UUID selection as an architectural decision, teams can avoid costly performance and operational pitfalls later.

Bottom Line

Choosing the right UUID version matters. It affects scalability, database efficiency, operational complexity, and privacy. Time-sortable UUIDs like v7, or reordered v6, provide better database performance, simplify observability, and support distributed systems. Random UUIDv4 prioritizes privacy, while v1 remains relevant for legacy systems.

Making a thoughtful, deliberate choice ensures your system performs reliably, scales gracefully, and remains operationally straightforward as it grows.

For teams looking to adopt UUIDv7 with confidence, Authgear's UUIDv7 tool offers a practical solution: it allows you to generate compliant identifiers, inspect their timestamps, and design systems that scale efficiently from the start.

Explore the Authgear UUIDv7 tool to generate compliant identifiers, understand their structure, and build systems designed to scale efficiently from the start.

FAQs

1. What is the main difference between UUIDv1, v4, v6, and v7?

UUIDv1 combines a timestamp and node ID, offering partial ordering. UUIDv4 is fully random, prioritizing privacy. UUIDv6 reorders the timestamp from v1 to improve sequential inserts. UUIDv7 uses a Unix timestamp plus random bits, making it fully time-sortable, privacy-conscious, and ideal for modern distributed systems.

2. Why should I consider time-sortable UUIDs like v6 or v7 for my database?

Time-sortable UUIDs maintain mostly sequential inserts, reducing index fragmentation and improving write performance. They enhance cache efficiency and make range queries faster.

These identifiers also improve observability, allowing you to infer event order without extra metadata, making them ideal for high-throughput databases, logs, audit trails, or distributed systems where efficiency and clarity are crucial.

3. Are there privacy concerns with using UUIDv1 or v6?

Yes. UUIDv1 and v6 expose timestamps and node identifiers, such as MAC addresses, which can reveal internal system details if exposed externally. For public-facing applications, this may pose privacy risks.

In contrast, UUIDv4 is fully random and UUIDv7 only reveals timestamps, making them safer while still supporting time-based ordering.

4. How do I generate UUIDv7 safely in my distributed system?

UUIDv7 can be safely generated independently across nodes, ensuring global uniqueness and time ordering. Tools like Authgear's UUIDv7 tool simplify this process, allowing you to generate compliant identifiers, inspect embedded timestamps, and verify structure.

Using such tools ensures seamless integration into distributed systems while minimizing collision risks and operational complexity.

For production applications, consider how UUID generation integrates with your JWT authentication strategy for stateless, scalable systems.

5. Can I migrate existing systems from UUIDv1 or v4 to UUIDv7?

Yes, migration is possible. Moving from UUIDv1 improves ordering and privacy, while upgrading from v4 adds chronological order. A typical approach generates UUIDv7 for new records while retaining old identifiers for backward compatibility. Proper planning around database indexing, storage, and application logic ensures a smooth transition without affecting system performance.

‍