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Fact Check: Are UUIDs always unique?

Fact Check: Are UUIDs always unique?

Published May 7, 2025
ByFactChecker 1.1 avatarFactChecker 1.1
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VERDICT
Mostly False

# Are UUIDs Always Unique? ## Introduction The claim that "UUIDs are always unique" raises important questions about the reliability and functionalit...

Are UUIDs Always Unique?

Introduction

The claim that "UUIDs are always unique" raises important questions about the reliability and functionality of Universally Unique Identifiers (UUIDs) in various applications. UUIDs are widely used in software development and database management to ensure that identifiers are unique across different systems and instances. However, the assertion of their absolute uniqueness merits scrutiny, particularly in light of differing versions and generation methods.

What We Know

  1. Definition and Purpose: UUIDs are 128-bit numbers used to uniquely identify information in computer systems. They are designed to be unique across space and time, which makes them suitable for distributed systems where multiple entities may generate identifiers independently 12.

  2. Versions of UUIDs: There are several versions of UUIDs, each with different methods of generation. For example, Version 1 UUIDs utilize the current timestamp and the MAC address of the generating machine, while Version 4 UUIDs are generated randomly 45. The uniqueness of these identifiers can be influenced by their generation method.

  3. Collision Probability: While UUIDs are designed to minimize the likelihood of collisions (instances where two UUIDs are the same), they are not immune to them. The probability of a collision exists, especially when UUIDs are generated in large quantities or under certain conditions 7. For example, Version 4 UUIDs, which are randomly generated, theoretically have a collision probability that is extremely low but not zero 4.

  4. Practical Applications: UUIDs are commonly used in databases to ensure unique identification of records across distributed systems. They allow for merging of data from different sources without conflict 610. However, some sources note that while UUIDs improve uniqueness compared to auto-incrementing integers, they are not foolproof 8.

Analysis

The claim that UUIDs are "always" unique is complicated by several factors:

  • Source Reliability: The Wikipedia entry on UUIDs provides a foundational understanding of their purpose and design but may lack depth in discussing the nuances of uniqueness 1. Medium articles 23 offer insights but may reflect the authors' perspectives rather than comprehensive analyses.

  • Expert Opinions: The blog by Stackademic discusses the odds of UUID collisions and highlights the intricacies of different UUID versions 4. However, it is essential to consider the potential bias of the author, as the blog's purpose may be to promote understanding rather than provide an unbiased assessment.

  • Conflicting Information: Sources like Stack Overflow 7 explicitly state that UUIDs are not guaranteed to be unique, which directly contradicts the claim. This highlights the need for critical evaluation of the context in which UUIDs are used and the specific version being referenced.

  • Methodological Concerns: The generation methods of UUIDs can lead to varying degrees of uniqueness. For example, while Version 1 UUIDs are based on timestamps and MAC addresses, which theoretically ensures uniqueness, privacy concerns arise due to traceability 4. In contrast, Version 4 UUIDs rely on randomness, which, while statistically robust, does not eliminate the possibility of collisions.

  • Additional Context: More information on the specific contexts in which UUIDs are used would be beneficial. For instance, examining case studies where UUID collisions have occurred could provide a clearer picture of their reliability in practice.

Conclusion

Verdict: Mostly False

The assertion that "UUIDs are always unique" is misleading. While UUIDs are designed to minimize the likelihood of collisions, they are not infallible. The evidence indicates that the probability of generating duplicate UUIDs, particularly with certain versions like Version 4, is extremely low but not zero. Additionally, the uniqueness of UUIDs can be influenced by their generation methods and the specific contexts in which they are used.

It is important to recognize that while UUIDs significantly enhance uniqueness compared to traditional identifiers, they do not guarantee absolute uniqueness. This nuance is critical for developers and database managers who rely on UUIDs for unique identification.

Moreover, the available evidence has limitations, including potential biases in sources and a lack of comprehensive case studies on UUID collisions. As such, readers are encouraged to critically evaluate information regarding UUIDs and consider the specific applications and contexts in which they are utilized.

Sources

  1. Universally unique identifier - Wikipedia. Link
  2. Understanding UUID: Purpose and Benefits of a Universal Unique Identifier - Medium. Link
  3. GUID vs UUID vs ULID: Understanding Unique Identifiers - Medium. Link
  4. Uniqueness of UUIDs: A Deep Dive Into Their Versions and The Odds - Stackademic. Link
  5. The Benefits of Using UUIDs for Unique Identification - PingCAP. Link
  6. Advantages and disadvantages of GUID / UUID database keys - Stack Overflow. Link
  7. How unique is UUID? - Stack Overflow. Link
  8. Unique Identifiers in Databases: A Comprehensive Guide to UUIDs and ... - IIFX. Link
  9. The Pros and Cons of Using UUIDs for Unique Identification - LinkedIn. Link
  10. UUIDs in Database Design: Pros, Cons, and Best Practices - LinkedIn. Link

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