Home Advantages and Disadvantages of UUID

Advantages and Disadvantages of UUID

What is UUID?

A universally unique identifier (UUID) also known as globally unique identifier (GUID) is a 128-bit number used to identify computer systems information.

UUID Versions

  • V1 – Generated based on server’s mac address & current timestamp. (predictable)
  • V3 – Generated based on the MD5 hash of namespace and name. (high probability of duplicate)
  • V4 – Completely random. (unpredictable) (preferred version)
  • V5 – Generated based on the SHA-1 hash of namespace and name. (high probability of duplicate)


  • A UUID never guarantees a unique record.
  • There are 340,282,336,920,938,463,463,374,607,431,768,211,456 possible combinations.
  • There is a ratio of 1:340282336920938463463374607431768211456 chance of getting a duplicate.
  • There is 2.9387361 x 10^-39% chance of getting a duplicate.
  • There is a higher chance of getting hit by a bolt of lightning in your lifetime with 1:72000000 chance than generating duplicate UUID.


  • It is presumably unique across every table, every database, every server.
  • It permits straightforward merging of records from totally different databases.
  • It allows easy distribution of databases across multiple servers.
  • Most replication scenarios require UUID/GUID columns.
  • IDs generated are hard to guess.
  • It can be generated outside the database. A Ruby example is SecureRandom.uuid.


  • It is a banging 4 times larger than the normal 4-byte index value.
  • It is harder to debug. Imagine writing an SQL query like WHERE user_id='12e986e5-7b58-4e0b-aafe-e78c081e8410'.
  • New records are inserted at random positions because it is not sequential.
  • Drop in index performance.
  • Extra configurations are needed.
  • It is database dependent if generated using a database function.
  • It generates ugly URLs if you don’t use slugs.


A simple benchmark was created on a Ruby on Rails app using a User model with columns fname and lname using Benchmark.ms.

The record count of the model is thirteen (13) and shows the following result using the code Benchmark.ms { User.all }:

80.17600001767278ms (with UUID)
58.52800002321601ms (no UUID)

When should you use UUIDS?

  • When you don’t want the IDs to be predictable by the user. Eg. If there is /user/100 there must be user/99, and so on.
  • When you need to secure the record count of your database. Eg. A user registered on your site and its profile link is /user/100 he can, therefore, think that he is the 100th user to register on the site.
  • When you don’t want to have collision on multiple instances of databases.
  • When you need to use some advantages stated above.


It is never necessary to use UUID. UUID’s ought to be used as a final resort once you have tried all alternative means of determining uniqueness on your architecture. It is recommended to avoid because of the performance limitations in indexing their values. UUID’s are also not particularly friendly to users.

This post is licensed under CC BY 4.0 by the author.

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