How to Optimally Store SHA1 Hash Values in MySQL: BINARY(20) or VARCHAR(40)?

Storing SHA1 Hash Values in MySQL: Choosing the Optimal Field Length

When storing the output of an SHA1 hash in a MySQL database, it's crucial to consider the appropriate length of the field that will hold this hashed value. This article explores this issue by examining various options and providing recommendations based on performance and storage efficiency.

Variable vs. Fixed Length Fields

For variable-length data, VARCHAR might seem tempting. However, since SHA1 values are always 160 bits long, using VARCHAR will waste space due to the additional byte required for length specification.

Binary vs. Hexadecimal Storage

The SHA1 algorithm returns a value that uses 4 bits per character. Storing this value directly would require a VARCHAR with a length of 40 characters. However, by converting the SHA1 value to binary using the UNHEX function, you can reduce the storage requirement to 20 characters, using a BINARY(20) field.

Performance Considerations

When storing millions of records, BINARY(20) proves to be more efficient than CHAR(40), as demonstrated by comparative tests. BINARY(20) requires less storage space, leading to improved performance on database operations.

Recommendation

Therefore, the recommended approach for storing SHA1 hash values in MySQL is to use BINARY(20) and convert the hexadecimal SHA1 value to binary using UNHEX. This method provides optimal use of storage space and ensures efficient database performance.

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