Problems with Using UUID as a Primary Key in MySQL

UUID (Universally Unique Identifier) is a standard identifier format used to ensure uniqueness across different IT systems. Its popularity stems from the ability to generate unique identifiers without central coordination. However, using UUID as a primary key in MySQL databases comes with several significant challenges. This article discusses these issues, their impact on performance, and best practices to minimize negative effects.

Structure and Types of UUID

A UUID consists of 128 bits and is often represented as a 36-character string (e.g., 123e4567-e89b-12d3-a456-426614174000). It can be stored in various formats, such as a string (CHAR(36)) or a binary value (BINARY(16)), affecting data management and performance.

Types of UUID

• UUIDv1: Based on timestamp and MAC address, potentially compromising privacy.
• UUIDv4: Randomly generated, most commonly used due to simplicity.
• UUIDv7: Time-space UUID using Unix Epoch timestamp for better ordering.
• UUIDv8: The latest version, allowing vendor-specific implementations according to RFC standards.

Performance Issues

1. Data Insertion Performance: One main issue with using UUID as a primary key is data insertion performance. MySQL uses a B+ Tree structure for indexing, allowing quick data retrieval. Due to their randomness, UUIDs can lead to frequent page splitting and tree rebalancing, significantly reducing data insertion performance.
2. Memory Usage: UUIDs take up much more space than traditional auto-incrementing keys (INT). Storing UUIDs as CHAR(36) can occupy up to 288 bits, while INT occupies only 32 bits. Even in binary format (BINARY(16)), UUIDs consume four times more space than INT. Increased memory usage affects index size and increases I/O operations, potentially slowing down the database performance.

Best Practices for Using UUID

1. Using Binary Format: To minimize memory usage, it is recommended to store UUIDs in binary format (BINARY(16)) instead of as a string (CHAR(36)). This reduces space requirements and can improve data operation performance.
2. UUID Versions Supporting Ordering: Using UUID versions that support ordering, such as UUIDv7 or UUIDv8, can improve data insertion performance. These versions generate more predictable and sequential values, avoiding page splitting and tree rebalancing issues.
3. Synthetic Primary Keys: Consider using synthetic primary keys, such as auto-incrementing INT, combined with unique UUID columns. This combination allows the benefits of UUIDs without the full cost associated with performance and memory usage. The primary key can be an auto-incrementing INT, while UUID can be used as a unique column for other purposes, such as data synchronization between systems.

Advantages and Disadvantages of Using UUID

Advantages

• Uniqueness: Guarantees global uniqueness, crucial in distributed systems.
• Security: Difficult to predict, which can enhance data security.
• Scalability: Allows scaling systems without central coordination of identifier generation.

Disadvantages

• Performance: The randomness of UUIDs negatively impacts data insertion performance and can cause index fragmentation.
• Memory Usage: Higher storage requirements and larger indexes.
• Complexity: More challenging to debug and manage compared to simple numeric keys.

Implementation Examples

sqlSkopiuj kodCREATE TABLE uuids(  
  UUIDAsChar CHAR(36) NOT NULL,  
  UUIDAsBinary BINARY(16) NOT NULL  
);  

INSERT INTO uuids (UUIDAsChar, UUIDAsBinary) VALUES   
('d211ca18-d389-11ee-a506-0242ac120002', UUID_TO_BIN('d211ca18-d389-11ee-a506-0242ac120002'));  

SELECT * FROM uuids;

Conclusion – Is it the Right Choice?

Choosing UUID as a primary key in MySQL depends on the project’s specifics and system requirements. In many cases, UUID may be an appropriate choice, especially in distributed systems where identifier uniqueness is crucial. However, for systems with high data insertion intensity, it may be more beneficial to use traditional auto-incrementing keys or a combination of both approaches.

For more options on optimizing the database, you can read more on the MySQL Performance Blog.